Tektronix 2246 flickering screen, ch2 not working. (Ch2 fixed) New help needed! - Page 1
Forum section: electronics / repair

author: grusus
author_rank: Regular Contributor
timestamp: May 25, 2020, 03:02:45 pm
content: Hi.This is my first post on this forum so hello to everyone!I apologize in advance for my bad english. (I am from Poland)My friend gave me this scope for free few days ago. (It was thrown out of company where he works). Don't know its history.I am trying to troubleshoot it. I am newbie to scopes repair. I have experience in tube amp build and repair, also in electronics in general.Everything is on video.https://drive.google.com/file/d/1GUUY_F4MY3gDyiwNQZAO2gofrW0KoW46/view?usp=sharingWhat I've done so far:Voltages within specs. 50mv ripple on +130V, others less than 5mv. (tested with voltmeter and another scope)Scope is responsive. All things seems to work fine but it burns my eyes with this flickering. Everything is ripped and cuted. Traces are not continous.Also I cannot see trigger indicator on screen (I was able to see it once with full intensity. I don't remember if it was readout intensity or A or B).About dead channel 2:Trace is somewhere but very weak and very distorted. Position seems to do nothing. No trace visible. (It can be spotted on beam find)Trace (I input 1kHz square) is ok at input of AT127. At input of U122 there is very distorted triangle, also on output. (on ch1 there is nice square).Many thanks for any hint where to start with.I use this service manual:https://www.tek.com/manual/2246-service-manualMine is very early model: 1Y 2246 B045340

author: grusus
author_rank: Regular Contributor
timestamp: May 30, 2020, 10:24:53 pm
content: Anyone?

author: grusus
author_rank: Regular Contributor
timestamp: June 18, 2020, 07:28:24 pm
content: I have changed all electrolitics on all boards, and checked other caps against shorts. This helped a little.I was checking all test points with another scope and found something interesting.Schematic on page 323, Waveforms on page 319. - I will refer to them in my post.TP 6A and 6B looks fine. (pins 3&5 of U802)Pin 1 is readout input. Looks like 6A but with lots of garbage. Its shaking also. I think it should looks like 6AOn the output of U802 Pins 12&13 +8,8V's are spot on. However 6D is square with lots of garbage but very low amplitude (many times less than it should be) and 6E is more like square also but higher amplitude than 6D.6H&6I -58V and -88V. And also like square wave. They Don't even looks like they should.Any sugestions where to look next rather than changing U802? ( tek234-0401-21)Also does anybody know where I can get it from along with at127? Maybe some direct replacement's?

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: June 18, 2020, 08:40:14 pm
content: I'd start checking around the circuitry for the Z-Input, itlooks like it is blanking. However, the text should never be affected, Z-Inut is gated to the traces only.The high voltage seems ok, or you would see the image pumping in size as well, but it just blanks.As the backlight of the buttons are flickering as well, you do have a power supply problem somewhere. If all rails measure ok, a bad ground connection might be the trouble.Check the ground points.

author: grusus
author_rank: Regular Contributor
timestamp: June 18, 2020, 10:52:49 pm
content: Yes flickering of backlight of the buttons stopped after recap. Now only cuted traces with blank spots is the problem and flickering of the readout(when readout is turned ccw flicker of traces and ghosts on crt dissappears). I suspect horizontal circuit as I mentioned in previous post.Q809&Q810 and surrounding resistors are ok. Voltages around also. I will check test points for z input tomorrow, as i ended checking on horizontal amplifier because i found issue there.Image in size is rock steady.

author: grusus
author_rank: Regular Contributor
timestamp: June 20, 2020, 09:21:14 pm
content: I made some photos of traces.V/div and time base like in service manual.6A:https://photos.app.goo.gl/3JPDuHeFoFpadMsQA6B:https://photos.app.goo.gl/Qw58roiYCzeScTVQ7When I go from A sweep to B sweep I see this:https://photos.app.goo.gl/yyLausR5frKo5FMv5Trace is on left half of screen.(that was from time I get the scope)When I turn sec/div 1 position ccw i get this:https://photos.app.goo.gl/aiXmWaZn2VDtXKoc96B then is:https://photos.app.goo.gl/nkmv5ZFTY3fGdKAP9Turn sec/div back one position cw I get this:https://photos.app.goo.gl/UUfgEAHQD5jTt4tUA6B Looks this:https://photos.app.goo.gl/JAdj8BHENuPWcrm26I think that is not a normal behaviour.6C:https://photos.app.goo.gl/zTbj4Fm3LGL17TYu76D:https://photos.app.goo.gl/UNecEuXAGtQXzjSR76E:https://photos.app.goo.gl/yiykE79w3CnfjKah96F:https://photos.app.goo.gl/4Z1engjbXPfp5hzM86G:https://photos.app.goo.gl/RjmTHAermev4fa9r66H:https://photos.app.goo.gl/XJtnovY3V2vqp9TV76I:https://photos.app.goo.gl/NaW8gZc32HAAKFuX8Scope behaves like this (previous video was before recap):https://photos.app.goo.gl/GMHjh4wK8cWLfcCc9I am wondering why holdoff is influenciing traces the way they cuts, and also readouts flickers more or less with different position of holdoff. Also scale ilumination has influence on overall flicker.Other thing I noticed: There should be grid with dots all over crt when readout is turned on (seen on others video). Here they are present but they are jumping/floating around from left to right very quick.Other thing is Pin1 of U 802 is Readout horizontal input and looks like this:https://photos.app.goo.gl/TYZogpEe5RccrkTXAOutput of U801A Pin1 is:https://photos.app.goo.gl/tDQGWUuNRZYTp7jMAhttps://photos.app.goo.gl/aWBX1pYvkmcbiNAq8I am wondering if there is some timing issue, considering strange behavior in b sweep and no stable matrix of dots with readout. Maybe it is influencing also a sweep and overall performance. Where to look for it?As I said, I am noob in scope reapirs, trying to learn from people who are much better than me. This is for my personal use. Any help like "look in baseline stabilizer" or similar will be apreciated.Many can say buy a working scope. There are two things: Money (good scopes cost a lot) and It is nice to use equipement that you have reapired yourself.:-)Also scope behaves very odd when it is cold. It must run for 5 minutes and is operational as on video in this post. For first 5 minutes uncal are blinking, brightness of crt varies. and eventualy it gets as bright as it shold be. There are random brights up during first 5 minutes.

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: June 21, 2020, 07:11:03 am
content: Some Questions:- Does that behaviour change when switching between alt and chop mode?- Does the Z-Input work?( If you don't have a signal generator, just connect a x1 Probe to the Z-Input and connect it to the probe calibration signal output.)Seeing your latest video, that still looks like something is messing with the Z-modulation.

author: grusus
author_rank: Regular Contributor
timestamp: June 21, 2020, 03:02:22 pm
content: First few minutes of operation at cold start up(left off overnight).:https://photos.app.goo.gl/P1hn33ym8zmrWHf27QuoteSee video:https://photos.app.goo.gl/3y8rhsYRvHtdtoLF7QuoteMy signal generator is 0-3,8V square at 10000Hz. Multimeter shows ac on output of generator.See video:Holdoff full cw:https://photos.app.goo.gl/JbHSfhqot4DuVBZc7Holdoff full ccw:https://photos.app.goo.gl/beh9krctcym6mdWu5Checkpoints for section 7:7A(anyway):https://photos.app.goo.gl/2voArUPeh4qS8oAM77B: Depends on holdoff.This on tek:https://photos.app.goo.gl/B7ei2vxfaX35P9YW9trace looks:https://photos.app.goo.gl/ZMjuvxZPSwTz9AoJAthis on tek:https://photos.app.goo.gl/Hk8MGtZCGgPjw3my8trace looks:https://photos.app.goo.gl/huYczBLZrrw8SxjW67C: Depends on holdoff.https://photos.app.goo.gl/LFUxoA8wwQjjJtdw7https://photos.app.goo.gl/99Y7NfJwRfvhgpmU6https://photos.app.goo.gl/K82T6La1LGzt31CEAhttps://photos.app.goo.gl/sBLsmgU9NNVajgq5Ahttps://photos.app.goo.gl/ZxofgTiG7vvKeQDB6https://photos.app.goo.gl/ZDvX1hREvr1aBVrD97D: Depends on holdoff.https://photos.app.goo.gl/dHvrPipXEp4YxyxBAhttps://photos.app.goo.gl/2H6EixohswGeUW8c7https://photos.app.goo.gl/yPV5CqQVKiBSJeb4Ahttps://photos.app.goo.gl/JbW4rP3TNA53VUN467E: Depends on holdoff.https://photos.app.goo.gl/EKwC5WRDbWFPBohV6https://photos.app.goo.gl/QDmCpjis3Jv2z6GW9https://photos.app.goo.gl/Z9VCj3J3K1p22MdEA7F:https://photos.app.goo.gl/PdQibb7xX2jkq7NR77G: Depends on holdoff.https://photos.app.goo.gl/NnhESPna2Mwwy4Be7https://photos.app.goo.gl/CE6haQ9yMV56bVcP9https://photos.app.goo.gl/z7XWvvEqqBM1Bv7S67H:https://photos.app.goo.gl/r7HUTTbfo6QdFEkt57I:https://photos.app.goo.gl/be7f5bMUvqWU9JBk9I dont know what to think about it. Any hint?

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: June 21, 2020, 08:39:27 pm
content: Okay, we can learn a couple of things here:The blanking changes when we switch between alt and chop.Quick theory ofvoperation recap:In chop mode, the scope switches between the two inputs during the trace, instead of drawing the traces after each other.Chop is used to display the two traces time synced. When it changes to the other trace, the scope briefly blanks the trace to avoid drawing lines between the traces whenever it chops to the other trace. Generally, the same circuit that does the blanking in chop mode, also serves the Z-Input. I am on mobile now, so i can't dig into the service manual of this particular scope. When you switch to alt, the blanking stops (or just sees the blanking from Z-input, as I don't know if the Z-Input was active in your first video).So you need to look into the part of the circuit that creates the chopper frequency and does the trace blanking. Read the circuit descriptions, those are usually very good in Tek service manuals. Don't measure any test point for now - first, really wrap your head around the circuit and understand how it works.As those gaps in the trace are very wide, i wonder whether the chop frequency is simply too low. Do the gap "pauses" change with different timebase settings? Locate the source of the chop frequency for starters and check it.

author: grusus
author_rank: Regular Contributor
timestamp: June 21, 2020, 09:38:09 pm
content: External Z-axis input is active only on those two videos:QuoteDifferent timebase settings makes chops wider or more narrow. To make them pause I must adjust the holdoff. Even if the do not pause, they are there but scrolling very fast throu whole waveform.(Don't know if you can see this on video).I will check service manual for that and reply to you when i will get into some thoughts.I am not in a hurry with this scope, so if you will manage to locate yourself the source of chop frequency before me please reply.I have surgery in hospital from june 29, and will be off in hospital for 5-7 days. So no panic, no hurry :-)

author: grusus
author_rank: Regular Contributor
timestamp: June 21, 2020, 10:31:21 pm
content: Manual p. 53 explains it as I think.As I think:Clock for chop blanking is generated at U600 pin 18, then goes to U602. It is test point 4F. Clock source is 10MHZ crystal oscillator that goes to pin 1 (TC) of U600There is also another clock input to U600 pin 2 (LFC), from probe adjust circuitHoldoff is also connected to U600.If what I am thinking is right, I should test 4F (blanking generated by U600), 4G (10MHZ crystal input to U600), 4H (the other clock input to U600).I will do that tomorrow. :-)Also I found something in Troubleshooting scopes by tek on page 40 (46 according to pdf reader):https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdfFrom what I have noticed all neons are propably good - they flash during turning off the scope.HV caps tested with ESR meter and capacitance meter - good. I do not have HV leakage tester that can go almost 3kV.Heather to cathode leakage in unblanking circuit? Where to look for it? They do not mean crt heater to cathode leakage? But when there will be leakage from cathode to heater of crt neons should light during normal operation? I am confused.

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: June 21, 2020, 10:50:00 pm
content: I don't think it is leakage in the CRT, the blanking looks too digital.Also, check the selection circuit. The 2246 has separate pots for trace A, B and the readout, which is nice.Depending on what the scope is drawing, the right intensity signal must be fed into the blanking circuit, test point 7B.U602 must select*one*, and only *one*intensity from the opamp U1001. It will switch one of the transistors Q1001 through 1004 on. Q1005 is controlled by the Z-input.Check:Q1001 to Q1005 - if failed short, two signals get mixed.CR1001 and CR1002, these mix Z-Blanking into Intensitiy A and B. If they fail short, A and B get mixed.Edit: The chopper frequency is 1,25MHz with 200ns blanking, so in chop mode you should see a signal 600ns ON, 200ns OFF at 7B.As your second cope is anaolog, you will be facing some trouble triggering that - the scope will update the readout in between traces, so disable that. But looking at your screenshots, you already figured that out yourself.You will still get an additional blank during flyback of the trace to the left, just select a low timebase setting on the dead scope and you'll be fine.

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 22, 2020, 01:20:20 am
content: The 2246 has an adjustment (R724) for Readout Jitter, the procedure is paragraph 7 of Section 5 of the service manual.I think BreakingOhmsLaw is on the right track and adjusting R724 is not likely to correct the problem, but may reveal some additional clues. It would be wise to mark R724 before altering its setting.RF+ Tech

author: grusus
author_rank: Regular Contributor
timestamp: June 22, 2020, 02:14:53 pm
content: Mine doesn't have R724. It is very early model.(look at the end of first post) R724 was my first thought after reading service manual :-)https://photos.app.goo.gl/Q6k2vWTNtEyj51gD6I was monitoring pins 17-20 of U600 while changing A alt and B + regulating RO intensity.Only A:Signal is present on pin 17. other three are very low with some garbage. RO makes signal on pin 20 to come up, also is added to pin 17.Alt:Signal is present on pins 17,18,19. RO intensity makes signal on pin 20 to come up + also added to 17,18,19B:Signal is present on pin 18. other three are very low with some garbage. RO makes signal on pin 20 to come up, also is added to pin 18.LM324(u1001) is making problems? I have some on hand.EDIT:Maybe there is some kind of instability on U1001 making hf oscilation on 17-20pins of U600? I think this "garbage" as i said in upper section seems to be low level hf oscillation. I will check that and post photos in next post./EditQ1001-Q1005 seems fine. No shorts. Tested with diode tester in circuit and voltage drops seems fine all junctions.CR1001 and CR1002 also looks fine.7B in alt mode(.2V 1ms):https://photos.app.goo.gl/QhGybyn3vXNy9oet57B in chop mode(.2V 1ms):https://photos.app.goo.gl/S3BoaWg3VY6CK5yv57B in chop mode zoomed(.2V 1us):https://photos.app.goo.gl/Gtb8qJDQS4gA4yCz5Yeah readout intensity is always off :-) almost:-) during measurements.I have also DSO chinese small digital 1 ch scope if you preffer :-)About diagram 4 test points.Checked all just in case.4A:https://photos.app.goo.gl/k5QuiAPzVqiz13wz74B: depends on holdoff:https://photos.app.goo.gl/PkyR6uxqxPU9NBDQ6https://photos.app.goo.gl/VTEujTk2Zsu86k6x84C: depend on holdoff:https://photos.app.goo.gl/49W4HVX14epxr1Zh8https://photos.app.goo.gl/Kdji3TBwa1NLCTmw84D:https://photos.app.goo.gl/YTAzB3Hs9viSXXMx94I:https://photos.app.goo.gl/cNPhUh2RZvzVorETA4E:https://photos.app.goo.gl/6JjX9oXBrAuS5SoH64F:RO int at 0:https://photos.app.goo.gl/ns33sALJKYZi2Exu9RO int turned even slightly on:https://photos.app.goo.gl/eGSgmAS7FCeLDQ9J84G: 1v 0.2ushttps://photos.app.goo.gl/1ACwZaQpRGkPbM2v64H:https://photos.app.goo.gl/1jLUK3Bt47wggyqb7I think I covered everything :-)

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: June 22, 2020, 06:31:03 pm
content: Okay, 7B looks exactly what is is supposed to look like. Now we have this ruled out, lets take a look at the trigger circuit.I have the sneaking suspicion that it does not wait for hold-off timer to finish before starting the next trace.Let me dig into that circuit tonight and i will come back to you.Edit: Please select single beam, slowest timebase setting and verify that the holdoff oscillator is only triggered/running when the sweep has finished and not while sweep is running. TP 4I looks okay, but i want to double check if that is correlated to the sweep actually ending.

author: grusus
author_rank: Regular Contributor
timestamp: June 22, 2020, 09:21:07 pm
content: 4I: I think that this is not what you expected :-( Seems fine.https://photos.app.goo.gl/QTXHWLj9EJf8VA166U602 18,19,20 when A sweep is chosen without readout. 50mv@5mshttps://photos.app.goo.gl/xZKDYhFNxnyJy1x79EDITHere are at: 50mv 5us.https://photos.app.goo.gl/ydj7GjzREKoZAaqo6And direct output of U1001 pin 8 or 7 (same traces) 50mv@5ushttps://photos.app.goo.gl/5R73sjkcScU56Av58/EditWhile pin 17 of U602 is:https://photos.app.goo.gl/BMTQmJCUKCG5b6dM8Also I catched light ups on cold start up: (sorry for background music)https://photos.app.goo.gl/LufcFkhNoHkAHf9Y8Also trigger led is blinking.Another thing on cold startup. Even if i turn readout full ccw - they are still there.:https://photos.app.goo.gl/AoCZNrB3nLEbc57o9I am andjusting RO brightness only when they fully appear on screen on video. When the pattern is seen with barely visible readout, it is full ccw. (and yeah I have cleaned this pot and tested it many times - it is good)

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 23, 2020, 12:32:38 am
content: QuoteDuring the cold startup when the RO intensity is full ccw, is there a signal present on U602 pin 20??BTW, if you have not searched the forum, another 2246 owner posted last November, with Z axis problems. Although the OP never responded and the outcome is unknown, the same circuitry is involved:https://www.eevblog.com/forum/repair/tektronix-2246-z-axis-issues/The OP in that thread provided some DC measurements.

author: grusus
author_rank: Regular Contributor
timestamp: June 23, 2020, 10:24:09 pm
content: QuoteYes.https://photos.app.goo.gl/adxJmUETUFK9Zim1AMaybe you will not see it, but on cold start up pin 20 is almost the same as after some time. Thing is that when scope warms-up i must turn RO intensity up and then down and then pin 20 is quiet, and ghosting effect from readout on crt then dissapears with RO intensity turned full ccw. When sope is cold sometimes it do the trick, sometimes doesn't. But ghosting is always at turn on cold. Probably signal on pin20 of U602 either.I will check voltages in Z -axis tomorrow - run out of time today. I have searched forum and seen that topic, but as you wrote outcome from that topic is unknown.

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 23, 2020, 11:51:40 pm
content: Preset RO intensity control to mechanical center. At cold start, note if ghosting is present, U602 pin 20 noisy.Check U1001C pin 8 DC voltage and voltage at R506 RO control wiper side.Both should be close to zero Vdc, with pin 8 1.53 * RO wiper Vdc.Turn the RO intensity up slowly, check that U1001 pin 8 smoothly goes to +3.8 Vdc.Turn the RO intensity down slowly, check that U1001 pin 8 smoothly goes to –3.8 Vdc.Is there any sudden change at U1001 pin 8, when U602 pin 20 becomes quiet?Does cold spray on U602 or U1001 have any effect? Hot air?Following with much interest

author: grusus
author_rank: Regular Contributor
timestamp: June 24, 2020, 03:33:33 pm
content: I am back with some results :-)At the end is scan with measured voltages.I have noticed something today that I overlooked. No matter if scope is cold or warmed up, when I power on the scope with RO intensity turned full ccw this gosting effect is present till I turn RO Int slightly cw and then back - then it dissappear. Difference is that on cold startup i doesn't do the trick. Ghosting is present till scope warms up and I Use RO intensity the way I explained before.See video (actually i captured one of very rare situations when after restart with ro intensity turned ccw, there was no ghosting effect (usually it is almost always like on first start on this vid.). Those was restarts after warm up.https://photos.app.goo.gl/oeVBXWVrw1xtBbCL6In case we missunderstood of ghosting effect.Normally on this scope when RO intensity is turned up there is a matrix of dots generated with readout and readouts are displayed sharp with no blurr around and no flickering. In my case matrix of dots shakes and are blurry + they are running from lef to right of crt and readouts have blurr also, and are slightly dancing around + flickering.Voltages goes smoothly from 3,8 to -3,8 and also from 2,5 to -2,5.No sudden change on pin 8At mechanical center of RO int voltages are near zero V.I run out of cold spray - must order. Heating with hotair shorten time needed to make ghosting dissappear. U1001 during operation i s normally cold. U602 gets warm approx +50 degrees celcius (122 F).U600 is also cold as cucumber :-) Maybe slightly warm.I am slowly suspecting U602 is going bad. What should I check also to rule out or confirm U602 fault?Edit:Look what I found today:https://photos.app.goo.gl/RPQQkWBhBpVKKWdGADS2704 is glowing. I am pretty shure it didn't before. When I turn focus up it is glowing brighter. When down it dimms.New problem or indication of problem that already was there? :-) This scope will kill me. :-)

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 24, 2020, 10:11:01 pm
content: Okay, the DC voltages all look reasonable, so I think we can rule out the analog portion of RO intensity.I agree that U602 looks suspect, given that extra heat shortens the time for ghosting to clear. One can try ice in a plastic bag, to cool U602.How to proceed. Following W2304 (top left) pins 10.11.12 to sheet 11 shows each line is essentially not connected. The right end of R505, R506 and R507 each go to U506, a CD4051 multiplexer. There is a remote chance U506 may be defective and some crosstalk from another channel is interfering with the RO intensity signal. CD4051 is inexpensive and easier to change, than U602.Looking at U602 bottom left, address lines A0 and A1 provide control over which of the four intensity gate outputs are active at a given moment. If the address decoding inside U602 is knackered, then one or more of the other three intensity gates could be turned on while RO is active. Try removing Q1001, or just lift the emitter, to eliminate the /A intensity gate signal and see what effect, if any, this has. Then do the same with Q1003 and Q1004. What happens with all three intensity gate signals disconnected?DS2704 glowing, Channel 2 not working. This is mild.

author: grusus
author_rank: Regular Contributor
timestamp: June 25, 2020, 01:32:30 pm
content: Hi I was doing my weekly order from part shop and I ordered some cold spray and CD4051 + some other goods.Here are results. (removed all of mentioned components, not only lifting emitter.Q1001 removed only:https://photos.app.goo.gl/CwJFG4ygYeditFMV6That trace which i seen on crt: I was on A sweep and tried to move trace up and down and it was moving.Q1002 removed only (1001 back in place):https://photos.app.goo.gl/os2GupcJk6iPafud8Ghosting still present.Q1003 removed only:https://photos.app.goo.gl/gaJ9RwNB5SaXr91d9Q1001-1003 removed:https://photos.app.goo.gl/rrd5L59zoodTusMu5Q1004 removed only:https://photos.app.goo.gl/XWp3KixkNR3sSV6Z6Q1001,Q1003,Q1004 removed:https://photos.app.goo.gl/zL5ZL5GcCPRtqWCc8Q1001-Q1004 removed:https://photos.app.goo.gl/92KqESBrx1bUhvpW6Still you can see traces from A and B sweep. Even with A,B, RO intensity turned fully CCW.Checked Q1001-Q1004 out of circuit. Seems ok on transistor tester.Also checked CR1001&CR1002 out of circuit. Also seems ok. Tested on multimeter in diode mode and with T7 multi function tester.It is getting into suicide mission to make this scope working againTube amps, even those nasty ones are much easy to fix :-) Even laptop motherboards never made to me this much of trouble. Maybe that's because I know how to fix them

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: June 25, 2020, 02:52:13 pm
content: Perhaps the fault is in the blanking circuit itself. Are you bable to measure up to 3000V?Try:- single trace mode A, GND- Apply 3V to the Z-Input- hide readoutThe screen should be completely blank. If it isnt, the blanking circuit itself (past 7B) may be flawed. The circuit will generate a voltage up to 2700V, you need a HV probe to test.You can get a good one for around 150zł on ebay, they are no longer used much since CRT TVs are gone.

author: grusus
author_rank: Regular Contributor
timestamp: June 25, 2020, 03:25:49 pm
content: Here are the results:https://photos.app.goo.gl/x45VZydsNB8Pvrwm7Oops I bet that I have adjusted grid bias before.Here is after adjustment.https://photos.app.goo.gl/8HLGoy7qP2BrKCr39Can you pm me some links to good HV probes? My multimeter goes to 1000V DC (Brymen BM817)

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 25, 2020, 11:26:40 pm
content: Grid bias is relative to the cathode, just the same as in a tube amplifier. The absolute -HV is of somewhat secondary importance. As long as the trace can be focused sharply, the -HV is close enough to not be a concern.Simply adjusting the bias control to extinguish the beam, with 3 Vdc on the Z-axis input, will get closer to the optimum setting.Best would be to follow the Grid Bias adjustment procedure outlined in section 5-2. This procedure does not require a HV probe.

author: grusus
author_rank: Regular Contributor
timestamp: June 26, 2020, 12:39:26 am
content: I have adjusted grid bias following service manual, just before making second video from previous post. But i think I have done this week ago, maybe two.One thing i have done also after doing Q1001-Q1004 videos, I have change U1001 to lm324 just in case (had some free time, and got some in stock) I my scope there was NEC C324C. Maybe that is why adjustment was no longer correct.Any further Ideas?Many thanks for both of you guys for helping me.CD4051 will arrive on friday, so I will change it.I was wondering also:My 130V AC line is approx 122V AC. Maybe there is something drawing excesive current and pulling +130VAC down to +122VAC. I don't think this will be causing the problem with flickering and ghosting, but?OfftopicI was consideriing to buy HV probe anyway, because some tube constructions that arrives in my workshop have 1,5-2kV anode voltage and i had no way to measure that.My multimeter measures up to 1000V AC/DC and there were some situations that i have measured (and brymen showed correct value) about 1200V AC (with centertap) power transformer for tube amp 4xEL34 mono guitar amp. :-) 710 on anodes of each EL34. A lot :-)/Offtopic

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 26, 2020, 01:35:21 am
content: First thing, a comment about the videos. The ambient light level washes out the very faint detail on the scope screen, making it next to impossible to observe any detail in the video clips you have posted.As for the +130 Vdc measuring below specification at 122 Vdc. No relation to the Z axis problem. I have not yet checked the schematics, but I seem to recall +130 Vdc supplies the deflection amplifiers.Looking back at the other 2246 thread, the OP measured a variation of 4.5 to 4.4 Vdc, at the emitter of Q1001. The corresponding variation on your scope is 4.14 to 4.0 Vdc. The schematic indicates a normal variation of 1.1 Vdc.Both scopes exhibit Z axis problems. Both scopes exhibit the same minimal Q1001 emitter voltage variationWith 4.46 Vdc on each Q base and 4.2 Vdc on each emitter, each transistor is biased off. When the emitter is pulled down by the corresponding active-low gate signal from U602, that particular transistor would be biased on and the buffered intensity setting passed on to the Z axis amplifier.U602 is an ECL device, the intensity gate signals will only vary about 1 Volt in amplitude, between high and low states.The very next step would be to measure the DC voltage variation at Q1002, Q1003, Q1004 emitters, to see if they mirror the Q1001 emitter measurement.If this is the case, then it appears U602 is not gating the four transistors. Some portion of each signal bleeds through each transistor, producing the mash-up result observed.Before concluding U602 is defective, address inputs A0 and A1 should be observed. Each of the four outputs should go low (ECL low being 1.95 to 1.63 Volts less than Vcc, or 3.35 to 3.57 Volts, with Vcc 5.2 Volts) , corresponding to addresses 00, 01, 10, 11. This is a bit difficult to perform, as it requires three channels of a four channel scope. Or a logic analyzer that is known to work with ECL logic levels.As BΩL points out, trouble in the trigger logic could be responsible. Timing is everything in digital circuits and the RO anomaly can certainly be attributed to a timing (multiplex) defect. For reference, ECL high level is 0.96 to 0.81 Volts less than Vcc, or 4.24 to 4.39 Volts, with Vcc 5.2 Volts.edited to correct ECL logic levels min/max for Vcc = 5.2 Vdc.

author: grusus
author_rank: Regular Contributor
timestamp: June 26, 2020, 01:53:32 am
content: QuoteIf my thinking is correct:First probe on A0, Second on A1, third measuring pins 17-20 of U602?I can do it with scope itself. It is operational and I have 3 channels working. Flickering is not a big deal as I will get 3 square waves?If I am wrong, please correct me.QuoteI am sorry for that. I will pay more attention to that in the future. I will make those videos again tomorrow and paste them here.

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 26, 2020, 03:53:34 am
content: QuoteYes, this is correct. Trigger on A0, sweep speed adjusted to show four cycles of A0. A1 should show two cycles.The decode should be something like:Code:A0 A1 Gate output LowL L pin 17H L pin 18L H pin 19H H pin 20The exact order may differ, the important detail is that only one of the four outputs are low at each of the four possible addresses.When moving the third probe to another output, the position of that output low pulse should shift left or right of the first output probed. In this way, each of the four outputs should align with the corresponding address, as observed on channels one and two.If you find the results to be confusing, that would be expected - A0 and A1 are part of a wider address bus and the trigger may actually need to be taken from pin 40 /SIN - assuming this pin function is "chip select". When this pin goes low, the address codes are intended for U602, as opposed to another IC sharing A0 and A1.If further clarification is needed, just ask.

author: grusus
author_rank: Regular Contributor
timestamp: June 26, 2020, 02:35:34 pm
content: I did some measurements.Q1002 E is +4,56 - +4,45Q1003 E is +4,38 - + 4,29Q1004 E is +4,36 - + 4,26Checked A0 and A1, with pins 17-20 of U602. Only pin 17 is low, other 3 are high. When I change to B sweep 18 is low, others high. When I turn readout from full ccw to full cw trace is getting slightly lower(not on video)Here is video of pin 20 of U602.Top trace is A0, Middle is A1, bottom is pin 20.https://photos.app.goo.gl/ZEK7gZi9n6mB1TTZ6Going through pins 17-20. (This random dots on bottom trace is because of bad probe connection. It is hard to shoot video with one hand and measure with other one :-) )Top trace is A0, Middle is A1, bottom is pin 17-20.https://photos.app.goo.gl/dt1F4vMpkSrqr9KN8A0 on pin 38 of U602 only, on digital scope:https://photos.app.goo.gl/7Ev6gxwzNtJDnhVq5https://photos.app.goo.gl/gtVKDSQtmhAZ2drA7A1 on pin 39 of U602 only, on digital scope:https://photos.app.goo.gl/NUVxnMxVKg6wxnSD7https://photos.app.goo.gl/SAc1kvSvh8Qz3umM9https://photos.app.goo.gl/JCAPhzqTk48s3yd79Should they look like this? Especially A1?EDITAll in place:https://photos.app.goo.gl/DxPyb9omd31whon7AQ1001 out. Q1002, Q1003, Q1004 in placehttps://photos.app.goo.gl/WDsMbpKdTror1Y7W9Q002 out. Q1001, Q1003, Q1004 in placehttps://photos.app.goo.gl/P5EFFHctmCq4d1xZ7Q1004 out, Q1001, Q1002, Q1003 in placehttps://photos.app.goo.gl/gvvR6U4PAzSD1gUK6Q1001, Q1002, Q1004 out, Q1003 in placehttps://photos.app.goo.gl/m6ys8G62jeMhdUwS6All out.https://photos.app.goo.gl/jM918cqxfUxy7Byd8/EDIT

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 26, 2020, 04:54:24 pm
content: I owe you an apology about he videos.It was my browser causing a problem where only the first few seconds would play, then repeat. This was short enough that the trace never appeared on screen, leading me to think it was too dim to see. Lights out, nobody home on this end.The timebase setting is far too slow. Within the first few milliseconds, there are multiple high-low transitions occurring on A0 and A1. The timebase must be set to a much faster sweep (us or ns), so that each narrow pulse can be seen clearly. And external trigger connected to /SIN.Please make a video of Q1002 (RO) in, Q1001, Q1003 and Q1004 out. It is expected that the RO will be free of flicker.These emitter DC measurements are interesting. I wonder if the schematic values are actually the high and low DC levels expected, when the gate signal is off and on? This interpretation certainly fits with ECL levels. With the higher sweep speed, note if the gate outputs' high and low levels are displaced above zero Volts, by about 4.2 and 3.1 Volts respectively, with about 1.1 Volts peak-to-peak amplitude.

author: grusus
author_rank: Regular Contributor
timestamp: June 26, 2020, 06:45:25 pm
content: In my videos were lot of reflection so do not apologize :-).Some photos:Pin17:https://photos.app.goo.gl/NtrTs7vaotwJuZMQ7Pin18:https://photos.app.goo.gl/gZ1d2wX1WLBYkZPK7Pin19:https://photos.app.goo.gl/JVcxWVQkSZSJBV3b7Pin20:https://photos.app.goo.gl/buu77qKE2dVrANnx5I called my friend and he will lend me his 4 ch Uni-T digitall scope, but after my come back from hospital - next week.Q1002 in, Q1001,q1003,q1004 out.https://photos.app.goo.gl/5Cn6457dNGijtag2AQuoteI think i quite don't understand :-) At bases of q1001....4 there is only dc voltage. At C and E is square wave. with peak-to-peak approx 0,1-0,2V dependig which Q I am measuring.

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 26, 2020, 09:00:41 pm
content: QuoteCorrect. The circled 4,2V and 3,1V on the schematic are the square wave voltage levels expected on the emitter. When U602 pin 20 is ECL high, the voltage should be 4,2V. When U602 pin 20 is ECL low, the voltage should be 3,1 Volts. A DMM cannot distinguish between the two and this is why I suspect these circled voltages may actually refer to waveform levels. It is not just a coincidence that the two voltages *are* ECL levels.For clarity, CMOS logic low is zero to 1/3 Vdd and high is anything between 2/3 Vdd and Vdd.TTL low is zero to +0,8 Volts and high is anything between +2,0 and +5 Volts.ECL levels are as I explained previously.When U602 pin 20 waveform is at an ECL low, the voltage level observed on the measuring scope should be 3,1V above the zero reference line. Similarly, the high portion of the waveform should be 4,2 Volts above the zero reference.The objective is to measure the actual logic high and low levels, by counting divisions on the display, based on the number of divisions above zero reference, to the high and low portions of the gate waveform. With a vertical setting of 0,5 Volts/cm, 3,1 Volts would be 6,2 divisions above the zero reference on screen. If the probe being used is a 10x, then 0,5 Volts/cm is really 5 Volts/cm and 3,1 Volts would be 0,62 divisions.QuoteIf the total amplitude swing from high to low is only 0,1 to 0,2 Volts, then this is definitely a problem. The total amplitude should be 1,1 Volts. Q1001 through Q1004 are not being turned on by their corresponding gate signal. BJTs require about 0,65 Volts base-to-emitter minimum to turn on. 0,1 to 0,2 is inadequate.The video of only Q1002 in circuit is half of what I expected. The RO intensity works and the other intensity controls have no effect.The flicker is still present, but I am not ready to condemn U602 defective. Verifying the address timing is a challenging task. It would be nice find U602 is not being addressed correctly and failing to turn on its gate outputs when expected.I have been studying the Readout System on sheet 9, looking for another possible cause. Waveforms 9A and 9B, /RO Blank and /RO Request, should be checked.If you would like to take a break from this RO problem, here's something easy to address the channel 2 attenuator hybrid. Make up a chart of resistance measurements from AT117. No need to disconnect any leads.Code:pin 12 to pin 11pin 11 to pin 9pin 11 tp pin 1pin 1 to pin 2pin 9 to pins 8,10pin 11 to pin 7pin 7 to pin 6pin 6 to pins 3,5pin 4 to pins 3,5Compare to AT127, to see if there are any significant differences.Maybe your friend can smuggle his scope and your 2246 into the hospital?Might make the time pass much more quickly.

author: grusus
author_rank: Regular Contributor
timestamp: June 27, 2020, 12:02:01 am
content: Q1001...4 base voltage to gnd is 5V0,67-0,72 B-E voltage. depending on Q. When A sweep i active only Q1004 B-E is 0,2V and vice versa with only B sweep.Zero Line position is at very bottom of the crt. Coupling DC 1v/divCollector:Q1001...4: 5,8V to bottom of tracehttps://photos.app.goo.gl/fXVg9cgGWkFEpv1g6Emiter: A sweep is active, no readout.Q1001: 3,8 V to bottom of tracehttps://photos.app.goo.gl/NJa1jH7kFkRCFkPm7Q1002: 4,5Vhttps://photos.app.goo.gl/LpYPxe9EsiLikWwf9Q1003: 4,4Vhttps://photos.app.goo.gl/orG2o7E41NJGwnto6Q1004: 4,4Vhttps://photos.app.goo.gl/orG2o7E41NJGwnto69A: (U600 pin12) AC 10mv/div 1us/div When I turn cw readout intensity whole trace goes down.(not the amplitude)https://photos.app.goo.gl/Va62yfrc8Lz4ac6J69B: (U600 pin11) AC 50mv/div 0,5us/div When i turn cw readout intensity whole trace goes up. (not the amplitude)https://photos.app.goo.gl/JCWcLw8xvd4x9j3H6https://photos.app.goo.gl/nv2qfZffCfkxJNTj7At117&127pin 12 to pin 11 492K infpin 11 to pin 9 0 0pin 11 tp pin 1 0 0pin 1 to pin 2 0 0pin 9 to pins 8,10 inf infpin 11 to pin 7 4,5 4,2pin 7 to pin 6 inf infpin 6 to pins 3,5 inf infpin 4 to pins 3,5 inf infOnly noticable difference is on pin 12 to 11 (scope turned off). Maybe i will do some magic and cut trace after pin 12, put two 1m ohm resistor parallel and capacitor (measure it from AT117) with one in series :-) Just kidding :-)QuoteThat would be perfect :-) Unfortunately due to Covid-19 restrictions there are no other people allowed to entry to hospital than patients. Even my wife cannot visit me in hospital.No worries. I am going to hospital at june 30th(tuesday) and will be out at july 3rd or 6th (friday or monday) so not much time i will be off.

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 27, 2020, 02:29:52 am
content: Now it is getting even more interesting. The waveforms at 9A and 9B should both be close to 5 Volts p-p.I should mention that DC coupling must be used for all logic waveforms. AC coupling blocks the DC component, which is essential to DC measurement. Set the vertical to 1 V/cm, DC coupling, sweep 2 us for 9A and 50 us for 9B. Trigger set to negative-going and DC coupled. Let's see the DC level for 9A and 9B.QuoteThis is to be expected with AC coupling. When there is a step change in the DC level on the probe side of the scope input AC coupling capacitor, the other side of the capacitor responds by shifting the trace position.Something I should ask, does this 2246 have two small watch cells in holders? The 2246 I repaired had a fair amount of corrosion damage, from leaking cells.QuoteThis is another problem. Vbb3, from U604 pin 11 should be 3,85 to 3,97 Vdc, and present on the cathode of CR1005. The anode of CR1005 should be one diode drop (about 0,65 Vdc) higher. Current flow through CR1005 and R1028 dictates the anode voltage cannot be 5 Volts, neither can the bases of Q1001-4. Something is open circuit, CR1005, U604 pin 11 or a copper track or jumper W1000.AT127 - by all means, tack solder a 470k resistor external between 11 and 12. The high frequency response will suffer, but for a quick confirmation, this is what I would do.Thanks for sharing the dates of your upcoming "holiday." Do enjoy the attention of all the young ladies.edited to correct ECL Vbb3 voltage min/max, for Vcc = 5.2 Vdc.

author: grusus
author_rank: Regular Contributor
timestamp: June 27, 2020, 02:13:53 pm
content: Zero line at very bottom of the crt. V and s and trigger settings as you said in previous post.RO intensity 12 o' clock9A:https://photos.app.goo.gl/6ehPL4QWmazxthuu99B:https://photos.app.goo.gl/NYiVE8Zk1gM779w96RO intensity off.9A: (0,2V DC offset) ( 0 line in the middle of crt)https://photos.app.goo.gl/KBMfrirgywTKz5B17and with 0,1V/div:https://photos.app.goo.gl/edUxCbnDQYeMdexw89B: (5,2V DC offset)https://photos.app.goo.gl/H92fiaosCDa5v6jF6QuoteYep. I have change them, because they leaked. Only cell holders were affected. Cleaned everything. No trace damage is visible.There is one thing:My processor board is different from manual. It is not covered in service manual that i use. I cannot find correct one.https://photos.app.goo.gl/UQzj2Mvck7KNMwtW6Getting back to q1001-q1004:Cr1005 cathode is 3,858 V (same on U604 pin 11), Anode 4,45 VR1028 one side is 5,18 V other is 4,46 VRing out everything from U604 pin 11 to bases of q1001-4 looks fine.W1000 has continuity.I am litle suspicious about CR1005. 0,6 V drop diode test, 0,99V drop backwards. Tested in circuit.AT127This is another story.I just put new solder to pins 11 and 12 and values are good now. Checked one more time at117 and at127 and values are same. Still no trace on ch2. When I hit beam find button it shows it on very bottom (if ch2 is inverted it goes to the top). Position does nothing. Something is bad with vertical preamp for this channel.I am wondering if U122 is bad. I think, even this is tek part, it can be fixable.https://photos.app.goo.gl/3wDtDcViJRzAvd1L6

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 27, 2020, 03:19:57 pm
content: Okay, it looks like there may be two things causing some confusion. The +5 Vdc supply is actually +5.2 Volts and the scope vertical gain may not agree with your DMM.About 9A - is it not possible to set the triggering for a stable display? When triggered correctly, it should be possible to see a low pulse of 2 us width, as shown in the manual.9B is triggered cleanly, but the sweep speed is too slow. Try 2 ns and 50 ns for 9A and 9B. It is very difficult to male out the sweep speed units in the manual photos.The high and low levels for 9A and 9B look good.For U122, apply the same resistance measurement technique and compare with U112. If you do not already have them, locate a set of needle multimeter probes, also known as back-probes. These are tiny enough to probe within the ceramic hybrid without accidental shorts.Locate U220 - place DMM red lead on pin 14, black lead on pin 13. With scope on, no signal on channel 2, turn the vertical position control from ccw to middle and to cw. The expected behavior is that the DMM will show a decreasing voltage difference that passes through zero Volts near middle and increases with opposite polarity.CR1005 should be okay, the voltage drops all look good.I see how your processor differs from the board in the 2246 I repaired in 2017. Interesting.

author: grusus
author_rank: Regular Contributor
timestamp: June 27, 2020, 07:47:32 pm
content: 9A: triggered on rising edge (I can't do it on falling edge) Previously it was on falling edge.2us:https://photos.app.goo.gl/kmoGdKzSCoCY8MnV71us:https://photos.app.goo.gl/d1bukCsgSPAV8ppJA.5us:https://photos.app.goo.gl/jrBM8t5KHPjsyunE99B:20us:https://photos.app.goo.gl/3qebDvUWVrrUG3o6810us:https://photos.app.goo.gl/AVFUTe3Tbr9bH8Lm95us:https://photos.app.goo.gl/bsu3n9p5iNtw1o5V72us:https://photos.app.goo.gl/VqcHGZN9wMdMhBNc91us:https://photos.app.goo.gl/4cCYM4gm8dz98U3BA0,5us:https://photos.app.goo.gl/q4VMtxaw1ckya37F9Scope I am using is Siemens oscillar M07192 (another old scope, from 70's propably - i bought it 14 years ago used when I was studying electrotechnics at University). No documentation is there. No calibration guide. I didn't want to mess arround with calibration. I am just getting to know how to do it from tek2246 service manual. I 'd better trust my DMM than this scope for voltage mettering :-) I am looking forward to calibrate this siemens scope in future, after 2246 repair.U112 measured the same as U112Pin13&14 of U220 ch 2 no input, normal +1,38 to +1,39 (from ccw to cw)ch2 inverted: -1,37 to -1,38VPin 13 to gnd is 5,93VPin14 to gnd is 7,3VOn u210 those are equal 6,6Vhmmm.I was looking at schematic 2 - There is some kind of mixing RO with CH1-4 - vertical position switching. I am wondering if here could be source of all problems: U280,U202 maybe? What do you think?I know this processor board assembly (g-8928-03) was used in very early tek 2246 units. Also they were used in tek 2245 (bit earlier assy g-8928-02) not 2245a (they have same as in 2246 service manual). I tried to find service manual for 2245 but there is only for 2245a.

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 27, 2020, 11:14:22 pm
content: 9A and 9B look like the service manual waveforms, good job.The variable control I am referring to on the M07192 is the red knob in the center of the channel 1 and channel 2 vertical step attenuators, on the front panel. The marking is Verst Fein. Turn this ccw out of detent and note how the display amplitude varies in a continuous manner. This is what I am referring to, to get the scope and DMM to agree. This has no effect on the present state of calibration. This control is there for user convenience.QuoteDo I understand correctly that the resistance between the various pins measure the same?Channel 2 vertical position signal, -2,5 to +2,5 Vdc goes to U203B pin 5. The same voltage should be present on U203B pin7 and on U202 pin 5, which multiplexes other vertical position signals, that then drive U280. Had I looked at this, it would have been obvious the vertical position controls have no effect on U112 and U122.Can you take another photo of U122 that is even closer and with a little more light? It should be easy to create a schematic of this hybrid. I agree it may be repairable and I am suspecting the problem may be an open feedback path. Some of the silver SOT-23 numbers are familiar, Motorola/ON Semi parts.QuoteWe can certainly try to see what is happening here. Preset channel 1,2,3,4 and Trace Separation to middle of rotation. Alt. sweep 10 us/cm, channel ,2,3,4 on, no input.Connect channel 2 of the M07192 to W201, this will be the trigger signal, positive-going. Set the sweep to 50 us/cm. We want to see two ENable pulses. If my math is correct, there should be 400 us between the two pulses, since each sweep requires 100 us times 4 channels.With M07192 channel 1 (0,5 Volt/cm) probe on U202 pin 14, turn channel 1 position ccw, cw, back to middle. Repeat for channel 3 and 4. Then turn channel 2. If my theory is correct, there will be 1/4 of the waveform that varies in amplitude, for each channel. The time displacement corresponds to the active channel. 0-100us = channel1, 100-200 us = channel 2, etc.How the readout for each channel is interleaved or overlaid with the channel vertical position level is not clear from the schematic. It may be necessary to read the theory of operation, to understand how the RO is overlaid with the vertical signals. We'll just have to see what the first waveforms reveal.

author: grusus
author_rank: Regular Contributor
timestamp: June 28, 2020, 12:22:10 am
content: QuoteThis does what it should :-)https://photos.app.goo.gl/LRWDXj8kBWeJtksu9When I was making photos of trace 9A and 9B it was slightly off detent (approx 15 degrees) I doesn't have lock function, so adjusting v/div sometime makes red knob turns with it. I overlooked that. I will "calibrate" scope to DMM with var on scope tomorrow and make again 9A and 9B.QuoteYes. I made a mistake. Should be U122 measured same as U112.QuoteVoltages are spot on.U202:On pin 5 is 0,9V, but i think that You were thinking about pin 14- Voltage spot on.Pin 13 is output for channel 2 an it is from +1,1V to -1,1V same as on pin 1 - for 1st channel.QuoteAnd here we are hitting the wall.This is not a dual trace scope :-(It has 2 channels but only one trace is present on the screen. Maybe it is broken, but I have never make him to view 2 traces at the same time. We have to wait until next week when I will have digital scope.Although Siemens has ext trigger function so maybe this will help.QuoteHere you are:https://photos.app.goo.gl/wkqinhz7Fepd4Sc27https://photos.app.goo.gl/f7y39KPpPoQsUdmN9Wait... are those cracked solder joints on pins 1-15? I did measurement on pads not on pinsI wil reflow them and check tomorrow.

author: grusus
author_rank: Regular Contributor
timestamp: June 28, 2020, 12:04:53 pm
content: Reflow did nothing.I found in google that siemens scope should show 2 independent traces. So I have two broken scopes :-)

author: grusus
author_rank: Regular Contributor
timestamp: June 28, 2020, 03:29:23 pm
content: I have done some diggin.W201 50us with RO on:https://photos.app.goo.gl/YYDaUyNt6YUuWrgy5With ro off it is flat unitl I activate more than 1 ch.5ms/divAlso it blanks as screen is intermitent.https://photos.app.goo.gl/AhdK2SBdvxTFfgSL7Also noticed that it is only intermitent at ,5V div. ch1.https://photos.app.goo.gl/bSMSyMd6WVcGJMuN7W201 in chop mode 2us/div:https://photos.app.goo.gl/WZCrqALqmbYGSz8h6and with ro int turned on:https://photos.app.goo.gl/amsmCSrRDQczxSyH6Pin 5 of U202: Cannot trigger it better.https://photos.app.goo.gl/HLxLDQRtSVchcXF28https://photos.app.goo.gl/A98kgL4hpkpZk2wMAU280 pin 7 and 14 is trace position. Each of flat lines corresponds to ch1-ch4. They move within same ranges for all 4 ch.0,1V/div 5ms/divhttps://photos.app.goo.gl/3bXUWSwUbeBe89Zd7When RO intensity is turned on then:https://photos.app.goo.gl/fpYtv8GoSerbXaoJ6Pin14 of U202 is only DC voltage - flat trace.

author: rf+tech
author_rank: Frequent Contributor
timestamp: June 28, 2020, 09:55:08 pm
content: These waveforms are pretty much what I expected and I don't see anything unusual that could relate to the RO problem. I would like to seeQuoteWith a faster sweep such that channel 1 expands to fill the screen. Channels 2,3,4 off. The vertical intervals where the beam deflects downward to the RO position, are of interest.Now that you are gaining more experience with the M07192, we should revisit U602 pins 17,18,19,20. Each intensity gate signal should be switching between 3.1 Vdc and 4.2 Vdc, above zero reference. Ideally, only Q1002 should be installed. The other transistors should be left out, to exclude their contribution to the Z-axis amplifier. The RO shoudl be the only thing visible.QuoteAhh, but an old school analog scope is so much easier to repair.No schematics? No problem. When you are back home from your "holiday" in the hospital, start a new thread.If you are already familiar with push-pull amplifiers, this is exactly how the vertical channels function. Since the one channel is working, it is established that the vertical deflection amplifier is working. The problem exists in the preamplifier for the other channel - its output is most likely "railed", the beam is pushed very far off the top or bottom of the screen. This is very easy to confirm, with just a DMM.

author: grusus
author_rank: Regular Contributor
timestamp: June 29, 2020, 03:20:59 pm
content: Quote2ms/div only ch1 active. (when 4 ch are active each time portion is divided into 4, when 2 ch are active, same ammount of time is divided by 2. etc.https://photos.app.goo.gl/6YBDpbBhspKcL9L6AIt is shaking. I cannot stabilize it better. Also trace in the middle looks like it is running square wave.If you'd like even faster sweep - please let me know.QuoteOnly Q1002 present.DC coupling 1v/div - zero level at very bottom of crt (first grid horizontal line from bottom)Pin17-18-19 are same: (DMM = 4,11VDC)5ms/div:https://photos.app.goo.gl/QjAo8rtstNdmZdio6With readout:https://photos.app.goo.gl/CSJ1BVhD9US49DQz85us/div:https://photos.app.goo.gl/W1fETRyLoZKBSY7e7Pin 20: (DMM = 4,5VDC)With readout:5us/div:https://photos.app.goo.gl/7M75xZBWG3MjuWkS72us/div:https://photos.app.goo.gl/jJUd2mVXr9vedU7981us/div:https://photos.app.goo.gl/gq3oeEHz9WHWboeH8QuoteYes I am. When you input signal for ch1 trace is there. Also for ch2. Problem is that there is only one trace at same time and channels interacts to each other (you can change position of trace for ch2 with ch1 knob and vice versa) Also changing volts/div for ch2 changes position of ch1 trace and vice versa. So I think both channels are mixed together in not right way, but remember, I am noob in scope repairs :-). I will start new topic for siemens scope when I will be back.

author: grusus
author_rank: Regular Contributor
timestamp: July 04, 2020, 04:12:01 pm
content: I am back!!!

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 05, 2020, 01:45:38 am
content: The break has given me a new perspective on the RO problem. As I was reviewing the various videos, something finally clicked. The RO anomaly is actually part of a larger problem. The random vertical lines are a clue.From the theory of operation of the Vertical Preamps and Output Amplifier:QuoteThe important detail here is that the vertical displacement of the beam is the result of summing current from all four preamps, U210...U240. Disabled channels are *not* disconnected. I now suspect that non-working channel 2 preamp U220 is contributing garbage into the delay line driver and this is the cause of the random vertical lines. The RO jitter and shimmy is a side effect.The best way to test this hypothesis would be to disconnect one end of R250E and R251E, effectively disconnecting the output of U220.--The waveform with only Q1002 installed looks very good, levels are correct. U602 is free to go, after posting bail.Q1001,3,5 can be reinstalled.

author: grusus
author_rank: Regular Contributor
timestamp: July 05, 2020, 10:11:41 am
content: R250&R251 are integrated 4 resistors in one. I cannot pull out one leg of each one. If I will desolder whole R250 and R251 none of ch1-4 will work. I can desolder whole R250 and R251, bend legs for section E end solder it back in. Maybe remove U220? Of course, if without R250 and R251 RO jitter will be gone, we will proof that problem is before R250 & R251 in circuit.

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 05, 2020, 01:27:35 pm
content: Arg, resistor pack.Another option is to disconnect the RO vertical and horizontal signals, ahead of the vertical preamps and horizontal preamp. Removing one end of R207, near location 7C on Sheet 2, will disconnect the vertical dot position signal from the RO Display.Similarly, disconnecting one end of R807, between 4B and 5B on Sheet 6, will disconnect the horizontal dot position signal.

author: grusus
author_rank: Regular Contributor
timestamp: July 05, 2020, 02:22:45 pm
content: I have removed R250& R251.Result:https://photos.app.goo.gl/SE1GHKUyBsrCN4hu7I did some hacking with single 82R resistors and connected everything exept signals from ch2.https://photos.app.goo.gl/e3afstQL859aTzD77Now flat line from ch2 is present but no traces ofc.Flicker is still there.R207 and R807. I must locate them, because in this area board layout from manual doesn't match reality.

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 05, 2020, 03:55:41 pm
content: There is much unknown information to make a conclusion. The artifacts in the sine wave can be induced by selecting Chop mode and fast sweep speed. The beam has to deflect to each vertical channel position repeatedly, all within a single sweep. The result will be chopped up signals.Alternate mode displays one channel per sweep. Using ALT with fast sweep eliminates the chopping effect. Chop mode is best for slow sweep speed.Information essential to correct interpretation:Sweep speed setting?Chop/Alt mode setting?Signal frequency?Having a "before" and "after" video for comparison, with the exact same settings, signal, etc., would be of great help. It is becoming very time consuming to have to go back through this thread and try to locate another video for reference, that has different conditions, and try to interpret new videos.The video with 82 Ohm resistors installed suggests that U220 may not be the cause. Then again, this could be the result of Chop mode and fast sweep.To locate R207 and R807, measure resistance from W2302 pin 2 to U202 pin 4 - 714 Ohms is expected. With one probe on W2302 pin 2, see if it is possible to find where the resistance drops to 357 Ohms.W2302 pin 1 to U802 pin 1 should be somewhere between 75 Ohms and 575 Ohms, depending on pot R823 setting.

author: grusus
author_rank: Regular Contributor
timestamp: July 05, 2020, 07:02:01 pm
content: Quote0,5msQuoteI am changing it during video. I am intentionally showing not only crt, but you can see me changing alt/chop mode. It is in mode row where you select channels - last button in row. Default is alt mode. When button is lit it is in chop mode.Quoteapprox 1khz sineQuoteNoted. I will in future. I am still having extreme painkillers and, my thinking is very slow and I am feeling like drunk most of the time. Sorry for that.QuoteSo indeed R207 is where it should be, but instead of R807 i have a jumper wire with white plastic on it like those "W" elements on board. That is what misled me.Here is vid with R207 and "R807" removed (same settings as above):https://photos.app.goo.gl/rWxmq21DiYAjzUvY7Again I am changing between alt/chop. There is slight difference as it should be i suppose.

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 05, 2020, 08:39:43 pm
content: Here's a reference point: I've just replicated your test setup with a Tek 2465. In Chop mode, I see the same pattern of dots and they are more noticeable at lower intensity. In Alt mode, the dots disappear.So it is confirmed that only Alt mode should be used for the 1 kHz test, from now on.Next test. Can the test signal frequency be adjusted by a few Hz. to slow the marching dots to a stands-still and reverse direction?I would recommend leaving the RO signals disconnected for now. There is a secondary effect where several dots are not as bright as others. This could be an artifact of the video camera. If this is not a video artifact, then I would like to pursue this.No need to apologize for the medication side-effects.

author: grusus
author_rank: Regular Contributor
timestamp: July 06, 2020, 10:42:49 am
content: QuoteYes. I am adjusting on precision 0,1Hz scale up and down. Freeze of dots and going different directions is responding to freq adj. Behaviour of marching dots is predictable and recurrent. Alt mode.https://photos.app.goo.gl/hsNc2yL7Jvb1wJ1K8QuoteIn personal it is as in video.

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 07, 2020, 12:05:52 am
content: This screen capture below from the last video shows 8.5 repetitions/cmThis also correlates with the number of steps in waveform 9CSince both RO vertical and RO horizontal signals are disconnected, the anomaly must be Z-axis modulation. Set the beam intensity to clearly see the dashes in the 1 kHz sine wave. With the M07192 sweep set to 0.5 ms/cm, check waveform 7B, 7C and 7D. Is there any change when the RO intensity control rotated?In an earlier post, you mentioned DS2702 was glowing. DS2701 is connected in series with DS2702, so if one glows, so must the other.

author: grusus
author_rank: Regular Contributor
timestamp: July 07, 2020, 01:17:59 pm
content: I have noticed something. There is ripple on 7B,C,D that corresponds to marching dots on 2246. It goes left, stand still or right according to dots on 2246 crt.7B:https://photos.app.goo.gl/U7mJjkaLtiS6Uc9P6and "zoomed":https://photos.app.goo.gl/kKCkCCTgu1mhG5FZ9with readout (I am swiching from 0,5ms to 2us):https://photos.app.goo.gl/UVcsfYmPqSfqu4ap87C:https://photos.app.goo.gl/73QAbGGmrCtrqmz39with readout(I am swiching from 0,5ms to 10us):https://photos.app.goo.gl/33eHs2Gh3EGC8JpC87D:https://photos.app.goo.gl/hZjLkFKhXHh9Jn386with readout (I am swiching from 0,5ms to 20us):https://photos.app.goo.gl/bA1uwonSVkPfTazi7+/- 1khz sine input signal. I was adjusting by 0,1Hz as before. Alt mode. Only Ch1 active. R207 and R 807 disconnected. Also R250E and R251e.QuoteNo. It was DS2704 and only. Gets brighter when focus is turned more CW:Old picture.https://photos.app.goo.gl/RPQQkWBhBpVKKWdGANow it doesn't.I don't know if it is normal but when i rapidly turn focus from min to max, both DS2703 and DS2704 lights up and then goes off. They don't always behave like that. Sometimes they don't lights up.https://photos.app.goo.gl/hibvTLhka9EuZfVWAAnd with my luck my signal generator broke down :-). Lm741 is temperature sensitive. When cold works normally - when getting hot -failing. Cold spray does the trick. I must order one.

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 07, 2020, 03:52:06 pm
content: Please provide a photo showing the scope probe and ground clip connection, to the 2246.

author: grusus
author_rank: Regular Contributor
timestamp: July 07, 2020, 04:04:16 pm
content: 7B:https://photos.app.goo.gl/qKAXj1e9eYSbDp6XA7C:https://photos.app.goo.gl/v3T7VSd181wEG9xA77D:https://photos.app.goo.gl/KmwUht7EAeKV4aQt5Remember that in SM they present screenshots of traces 7B,C,D with 1ms/div. My starting point was 0,5ms/div as you said in one of previous post.

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 07, 2020, 05:44:03 pm
content: One more photo, farther away, that shows the proximity to the HV power supply.The "ripple" may be a probing artifact where the EM field from the HV switching supply gets picked up by the probe ground lead inductance.See this page for some examples of minimal inductance probing:https://www.eevblog.com/forum/beginners/diy-oscilloscope-probe-ground-spring/

author: grusus
author_rank: Regular Contributor
timestamp: July 07, 2020, 05:56:09 pm
content: Hmmm. I will check tomorrow if position of probe affects the traces on siemens scope.But, HV power supply is on other end and other side of scope with metal screen between boards. HV cable is also not in that area.In area where 7 C,D point are, there is -2,7kv in range of few centimeters.( max 2 inches)

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 08, 2020, 12:54:23 am
content: I've gone back to an earlier video and stepped frame-by-frame while observing the random vertical lines and RO wiggle. It appears each missing dot in any given RO character is the result of the beam being deflected to some point further up the display. These vertical lines appear in rows that most likely correspond to the six right-side RO menu rows.Further, each gap in the main sweep is also due to the beam being deflected to one of these six right-side RO menu rows. Since the horizontal and vertical RO signals are disconnected, the RO now appears as a single dot in the center of the screen. All that remains are the Z-axis "punch-outs".Working backward (Sheet 9) from the two RO position signals, DACs U2412 and U2413 are responsible for creating an H and V analog current for every RO dot position. For a given character dot to end up on the wrong line, would imply incorrect data from Character Dot Position ROM U2408. Or, the vertical DAC U2412 itself may be missing bits on the 8-bit bus. If this were the case, I would expect the effect should be stationary. What is seen appears to be that of a free-running clock that is not synchronized.Top left corner of Sheet 9 is where the Clock Divider/Counter is located. U2409 receives an 8 MHz clock, from U2501 Measurement Processor on Sheet 8.An end-to-end sanity test would be to trigger on this 8 MHz clock at U2409 pin 1 (waveform 9E) and probe U2412 pin 12. This pin is the LSB and should appear synchronized with the 8 MHz clock trigger signal. While you are at it, may as well confirm the other 7 data bits to U2412 are in sync. Also, check Vref+ and Vref- on U2412, pins 14 and 15 respectively. These should both be clean and steady DC. Photos or video are not necessary, unless something unexpected is observed.

author: grusus
author_rank: Regular Contributor
timestamp: July 08, 2020, 02:57:22 pm
content: QuoteYou're right. It was from HV. Moving probe around is makes ripple almost dissappear.Hmm. Clock is there but shouldn't it be a square wave?0.2 us/divUpper trace is clock, lower pin 12 of U2412https://photos.app.goo.gl/4QKXrbADmqK7prbR7and first on second:https://photos.app.goo.gl/YCW3gyDepwZfHgAh7as for other 7 data bits something is there with a little offset to clock as on pin 12. But they are with different amplitude and traces differ from each other.U2412 pin 14 and 15 ripple is 100mv. On dc coupling on scope shouldn't one be positive and one negative in reference to ground? Mine both are positive +4V.I have noticed sth today:Nothing connected to scope coupling to gnd (no matter if AC gnd DC). Alt mode. I managed to stop trace by adjusting holdoff. Look:1ch:https://photos.app.goo.gl/mzWKbEtigmFD7GNH64 ch active:https://photos.app.goo.gl/UdeeRcN33amEd3bn6Lenght of gaps varies. It is dependent to sec/div setting.https://photos.app.goo.gl/FmLdeRGztrMmzUY88Maybe this is normal for this scope, but I have never seen behaviour like this on any analog scope.

author: rf+tech
author_rank: Frequent Contributor
timestamp: July 09, 2020, 12:40:39 pm
content: The clock waveform squareness is in part, a function of the M07192 step attenuator over-compensation and scope probe compensation. A 20 MHz scope would have a 17.5 ns risetime, when properly calibrated. An 8 MHz square wave half-period is 62.5 ns. 17.5 ns is 28 percent of 62.5 ns. Adding over-compensation into the picture, what is observed is to be expected.Cross-checking the probe/scope combination with an 8 MHz square wave from a function generator (properly terminated), would be wise.The signal is suffieent to swing above and below logic thresholds, as evidenced by U2412 pin 2. Again, the limited bandwidth of the M07192 cannot faithfully reproduce these fast and narrow pulses. The signal is in sync with the clock and that is good.The other data lines will only be active when an RO line is enabled across the top of the display, where a higher dot deflection voltage is required.QuoteAn accurate assessment of ripple requires use of a ground spring/spike, as previously mentioned. This is even more important with fast rise-time digital signals. To understand why Vref+ and Vref- are both positive, please refer to the DAC-08 datasheet:https://www.analog.com/media/en/technical-documentation/data-sheets/DAC08.pdfR2415 establishes a reference bias current. One end is connected to +2.5Vp. Is this also 4 Volts?This newly discovered behavior of the hold-off control is another good clue. It is definitely not normal. I shall look into this later in the day.

author: grusus
author_rank: Regular Contributor
timestamp: July 09, 2020, 06:56:18 pm
content: I have checked clock on scope itself and noticed that on higher sweep retrace is visible and part of trace is missing/dimmed:https://photos.app.goo.gl/CUBXKJhQYkeZAVUv5https://photos.app.goo.gl/xPsAWDXgcVEqbzpF8https://photos.app.goo.gl/GHMqWpm6cuyGWvcn8I cannot find pot for retrace calibration in service manual. I am just thinking if those blank spots in traces and missing trace on higher sweep + visible retrace are connected, and this only one issue that causes all things?It looks to me that something is wrog with sweep on/off timing. Sweep is shut down after retrace, not before. This will cause a missing part of trace, and visible retrace. That just makes sense to me - maybe I am wrong.Also I have noticed that RO flicker is differrent when sweep ends and retrace starts, till speep starts again. It can be seen on video.https://photos.app.goo.gl/16HQSgQCLsWYF7PK8I didn't mention that before, but if holdoff is more cw - trace is getting dimmed slightly. when more CCW trace is brighter. I don't know if it mattters and if it's normal or not.Quotehmm. I cannot find that resistor. My board is different. In red rectangle is U2412. Pins 14 and 15 are connected directly to chip in yellow rectangle, pins 22&23. All that i have written on picture is what i think it is.

author: grusus
author_rank: Regular Contributor
timestamp: July 10, 2020, 09:43:51 am
content: Chip in yellow rectangle is U2408.Whoa, I made terrible mistake in pin counting...That screenshot i posted from pin 12 was ... pin 13 it is +v and it is around 5V. Pin 3 is -V and it is -7,5VPin 12 with clock:https://photos.app.goo.gl/U35fTyrV7PAsC4fA6https://photos.app.goo.gl/rBMKxpjbaxRmpFDC7But, I have nothing on pin 14 and 15. 0V. Only some ac ripple which corresponds to 8mhz clk.Found R2413 and R2415. One side is 0V both, other is 2,5V for both. Both measured 1,24k Ohms. What the heck? 2,4kohm to gnd from pin 14 for U2412 and same for U2413.

author: grusus
author_rank: Regular Contributor
timestamp: July 11, 2020, 12:21:56 pm
content: Update on ch2 not working.I did some digging around AT127, U122 and U220.I have disconnected out from At127 (pin 7) and voila - i have good signal on out of AT127.Next i have connected it back, and disconnected out of U122(pin 8 ) and gues what - good signal present there.So, or U220 is bad, or sth that is connected directly to it. Output is dissconnected (R250E and R251E)Any hint? It looks like sth is pulling signal down.

author: grusus
author_rank: Regular Contributor
timestamp: July 13, 2020, 05:57:47 pm
content: A little update on ch2.I was wrong.Signal was degenerated by U220. (varied of v/div position - that somehow mislead me)Failed TLC271 op-amp. (see picture)Now it seems all channels will be working fine.I swapped one from other channel - ch2 is working perfectly.Ordered one and waiting for package to arrive.Still flickering issue to fix.

author: grusus
author_rank: Regular Contributor
timestamp: July 16, 2020, 01:34:33 pm
content: UpdateAfter swapping tlc271 all channels are working fine. So this issue can be called fixed.

author: grusus
author_rank: Regular Contributor
timestamp: July 22, 2020, 01:51:31 pm
content: I just found more proper service manual for my scope. There are some minor differences between scope and schematics (no RO jitter adj) - other else looks exactly the same. Processor board matches. Also there are some differences in schematic 7 compared to previous SM (z axis, ctrl mux) that matches my scope.http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Tek/2246.pdfFrom now, I suggest to reffer to this new SM.Anyone have any hints and clues where to search for fault? I went through schematics many times, tested and I think i went into some kind of loop. Need some fresh look on this problem. If someone have knowledge, and will be kind enough to look into schematics in posted SM and give me some hint i will be greatfull. I think problem might be in digital part of scope - As those "blankings and jitter looks digital to me, not analog - but maybe I am wrong.As RF+TECH and Breakingohmslaw are not present on forum from a while (I hope they are fine) I am stuck with my thoughts.

author: grusus
author_rank: Regular Contributor
timestamp: August 01, 2020, 02:09:20 pm
content: After taking some break in troubleshooting this scope, I got back to it.After analysing service manual I got to the point that sth is messed up with clock/timing.I think this is corelated with visible retrace.Checked clock signal around U2409, U2508, U2507 - all seems fine. I am little concern about timer reset signal (+1VDC, no ac - only 8Mhz ripple from main clock - I don't know how it should look like), and INTR signal - also only dc no ac.Today I made small experiment and dissconnected RO BLANK (R2419). Readouts are much brighter, grid dot is fully present, readouts are less blurry and more stable.On Video I am connecting and dissconneting R2419.https://photos.app.goo.gl/341Lxitp8DYbE9R97That is why I am almost certain that there is some timing/interrupt/clock issue in this scope. It blanks when it shouldn't,Can anybody give a hint what to check next? How to address this problem?

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 02, 2020, 01:55:56 am
content: Your observation of the Hold-off control affecting the “chop” in the scope trace is a very useful clue. May I suggest reading the “DISPLAY AND TRIGGER LOGIC AND PROCESSOR INTERFACE” theory of operation, with special attention to the Chop Clock and Readout Interface descriptions.The important detail to note is how these two circuits work to mask vertical source switching transients from Chan 1-4, and various RO areas. The Hold-off Oscillator and Calibrator signals are used to derive the vertical blanking. If the blanking is out of step, these switching transients would be visible.To address your concern about the Timer Reset and INTR signals that seem to be missing: very narrow pulses (10s of nsec) with very slow repetition rates (in the msec range) are a challenge to observe on an analog scope. This may explain your observations.

author: grusus
author_rank: Regular Contributor
timestamp: August 02, 2020, 02:16:14 pm
content: INTR and timer reset are present. Thanks for explanation.After reading "DISPLAY AND TRIGGER LOGIC AND PROCESSOR INTERFACE", I decided to check again TC, LFC, OSCOUT pins of U600. TC and OSCout looks fine to me. But. LFC influences chop clock. LFC is 1,15kHz. front panel test point for 1KHz is also 1,15kHz. I am wondering if this could be the case. Manual says it should be around 1kHz - it's 15% off. My first suspect is C935. I tested 33pF in circuit. To remove this capacitor i will have to disassembly some part of scope (CRT, Pot board for intensity and focus) It is flush mounted on pcb and I cannot desolder it from component side. Hotair is also impossible - to many plastic elements in the way. If you think this potentially can be the case of problems with this scope I will do that.

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 02, 2020, 09:57:27 pm
content: 1.15 kHz is more than a little suspicious. You are definitely onto something.C935 is 22 nF, in the parts list as well as the schematic. 33pF suggests measurement error. Nearly 3 orders of magnitude lower C leads to nearly three orders of magnitude increase in calibrator frequency.The product of 22 nF and 22 kOhms yields a period of 484 usec, low and high, for a total of 968 usec. The reciprocal of this is 1.033 kHz. Checking the later 2246 schematic, we see R935 has been increased from 22 kohms to 24 kOhms. The calculations yield a calibrator frequency of 946 Hz. Given ceramic capacitors' well-documented decrease in C with applied DC, 24 kOhms is likely to be closer to the 1 kHz target.For the effort required to remove C935, it would be easier to solder another capacitor on top of C935. In theory, one could temporarily disable U930B by grounding pin 6, then inject a 1 kHz square wave of suitable amplitude into the CLK 1k point, to see if the chop anomaly disappears.

author: grusus
author_rank: Regular Contributor
timestamp: August 02, 2020, 11:05:10 pm
content: Yeah, I bet it is a measurement error. I have checked r935 - spot on 22,1k.C935 is not ceramic cap. It is a film capacitor in cubic plastic box. I connected 22n over C935. Frequency went down to approx 560Hz but no visible change on display in alt mode, nor in chop. I was connecting, and dissconnecting it live to see display in realtime. Main problem is somewhere else I think.I will extract this cap tomorrow from board and check capacitance. If out of specs - I will change it. Also will change R935 to 24K if i have in stock, or add 2k resistor in series.I checked in circuit also: R934=1k, R938= 2,2k, R939=1,2k, but 4,1V is 4,09 so... I will test all calibrator circuit parts out of circuit tomorrow.QuoteAlso will check that, but considering above, there propably will be no change on display.Hmm. I forgot to mention before but I was playing around with service menu. If I go to Proc board menu -> Readout menu -> Exercise RO interfece, Flicker is much more noticable. From theory of operation This forces communication between Measurement processor and RO processor. It's AD0-7, then D0-7, then R0-7. So maybe something that is connected to those lines is playing with us. Sorry I don't have enough knowledge and experience to troubleshoot this myself. Maybe I am totally wrong.

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 03, 2020, 12:23:01 am
content: Try 4.7 nF, 5.6 nF, 6.8 nF in parallel, whatever gets closest to 1 kHz.Also check the effect of Hold-off, with the extra capacitance.The objective is to remove gross error and rule out the effect, before moving on.

author: grusus
author_rank: Regular Contributor
timestamp: August 03, 2020, 02:17:05 pm
content: I tested whole calibrator circuit elements out of circuit. C935 was 20,5n so replaced with 22n. Also added 2K resistor in series with R935(didn't have 24K), Other elements tested fine. Now I have 1.000kHz/1.001kHz Clock at calibrator circuit. Close enough I think :-)I think now is slightly better - judge yourself.On Video I am adjusting holdoff, changing alt/chop and in the end when readouts gets dimmer I am connecting and dissconnecting ROBLANK R2419.Singal on input of the scope as always 1kHz sine :-)https://photos.app.goo.gl/9trA8izceGuTGZLe8I think main problem lies elsewhere.It looks like something is messed with blanking (ro blanking as examle above). + I don't know if you read this from my previous post that retrace is visible, and part of trace is missing on higher sweeps - from what I understand from service manual this is also corelated with blanking out of sync.Vid of RO exercise:https://photos.app.goo.gl/DeeB3DFPTxZrWYL99I was checking clocks around U2508B and U2507.Pin 9 of U2508B is 62,5kHz. Schematic says it should be 16kHz but in theory of operation U2508B divides 500K clk by 8 = 62,5kHz. Little confused...Others I think are spot on.

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 04, 2020, 03:24:30 pm
content: I am not seeing the retrace.I am seeing a diagonal stripe pattern of three or four intensity levels. Apply 1 MHz sine signal, level to fill six vertical divisions. Time-base set the same as for previous videos. The result on an analog scope would appear to be a solid band of light, the individual cycles will not be individually discernible. On the 2246, these diagonal stripes should be clearly visible.Adjust the Holdoff to make the stripes nearly vertical, for easy counting. The number of stripes will be of interest. Does the number of stripes vary with holdoff?Also of interest is the pulse width and count at U600-15. Refer to waveform 4D. At minimum holdoff, there are 50 pulses occurring during 4D high period. Note the discrepancy in sweep speed of 20 usec/div shown in the text above and the actual 10 usec/div in the photo. The latter is correct.Please check the actual frequency of the 10 MHz clock on U600-1.

author: grusus
author_rank: Regular Contributor
timestamp: August 04, 2020, 04:19:35 pm
content: QuoteI didn't post any vid and photo with visible retrace.1MHz on input. I am changing timebase settings on video, and adjusting horizontal position:https://photos.app.goo.gl/3VukWbH4Fjrazy5m8QuoteIf I understand you correctly: Is this what you want me to do? :-) I don't know about what diagonal stripes you are talking about ? I see only vertical.I am adjusting holdoff from CCW to CW, and meantime trying to tune to stabilise those vertical stripes. Number of stripes vary with holdoff. 18,36,72 stripes. Scope at 0,1mshttps://photos.app.goo.gl/5Ld5EVAupkwPpv4PAQuoteSiemens is on 10 usec/div.tek on 20usec/div: 50 pulseshttps://photos.app.goo.gl/x6W8LTLKp2pCkriYAtek on 10usec/div: 20 pulseshttps://photos.app.goo.gl/GDsr4bSS2Wp28tFn9tek on 5usec/div: 10 pulseshttps://photos.app.goo.gl/WwtBghKVgPg723i9AQuoteSpot on:(0,2usec/div)https://photos.app.goo.gl/U2b7Y1GX9m6x7wjBAAlso I have noticed few days ago (I forgot to mention. After repairing calibrator circuit there is no change), that time measurement on tek is 70% off actual input frequency. 1kHz input is measured as 1,7kHz - maybe it's off beacuse of bad calibration but will it be as much?

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 05, 2020, 01:29:38 pm
content: Please check the 10 MHz with a counter, for error that an oscilloscope cannot resolve.What is the period of the stripes seen in the second video?With R2419 disconnected, use an extra 1k resistor to tie the ROB input of U600-11 to +5V.Disconnect R2420, connect ROR input of U600-12 through 1k to +5V.This should be easy to accomplish at R2419 & R2420 locations, rather than on U600 pins.With both ROR and ROB disabled, the RO should not be visible.What effect does this have on the 1 kHz sine wave test signal?

author: grusus
author_rank: Regular Contributor
timestamp: August 05, 2020, 02:48:56 pm
content: Quotehttps://photos.app.goo.gl/YaRJLqcniEARwSuX6QuoteIf I understand you correctly Bars are approx 15ns, blank spots are approx 40 ns when there are 18 stripes on screen.QuoteFirstly I am at 1kHz sine, then at 1MHz.Both ROR and ROB pulled up to +5VHmmm. I don't know if you see that but When RO intensity is on there is ghost of trace generated by readout circuit. I am adjusting holdoff for almost whole video.https://photos.app.goo.gl/559uVo4ARrr8iF839Holdoff clk is from 130kHz to 70kHz depending on position.

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 06, 2020, 01:09:24 am
content: My bad, the /ROB input needs to be tied to ground to disable RO blanking, not +5V. /ROR is disabled with +5V.With RO blanking disabled, the RO intensity control should have no effect and the background signal should no longer be present.Let's see how the test signals look with the RO control signals fully disabled.

author: grusus
author_rank: Regular Contributor
timestamp: August 06, 2020, 01:32:48 am
content: ROB directly to ground, or through 1k resistor?

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 06, 2020, 02:20:03 am
content: 1k resistor.

author: grusus
author_rank: Regular Contributor
timestamp: August 06, 2020, 11:17:19 am
content: Hmmm.At first after starting scope there was no ghost of trace. It come on screen when I turned on more than 1 ch. They eventually didn't come off, even with only 1 ch active, nor after restart. Cold sprayed U600 and U602 did nothing, also major part of Processor board.See video:https://photos.app.goo.gl/ZcxqEbZbDCjDzPmh9

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 08, 2020, 02:35:14 am
content: The objective at present is to completely disable all RO related signals and see if this removes the gaps and extraneous dots in the trace.The residual RO dots are the result of Z-axis intensity modulation. Disconnecting Q1002 should prevent these from being visible.However...U600 cannot receive an RO Request and RO blanking is forced active, why are we seeing RO dots? Without commands, no RO dots should be generated.If Q1002 does not eliminate the dots, try disconnecting Q1001, Q1003 and Q1004 to isolate the source path.About the video: at the start, the waveform looks quite good. When the dots first appear, is the Holdoff being adjusted? This control is off-screen. Is it possible to put the camera on a small tripod, situated so all of the controls can be seen? This would greatly enhance interpretation and reduce the need to guess or ask questions.The Tek 2445/2465 manual goes into much greater detail on the Display Sequencer theory of operation. These models use a different IC with some additional signals, but is conceptually the same.Key points of operation are a full analog sweep of channel 1 (single channel active), followed by blanked retrace during trigger hold-off. Following retrace, the beam makes a fast horizontal sweep, while the character dots deflect the beam vertically. Z is unblanked to paint the individual dots. This entire process occurs during the hold-off period, which according to waveform 4D is about 58 usec. When the hold-off period ends, the next analog sweep occurs. So for a single channel active, there is one "frame" of analog sweep, followed by a "frame" of RO and cursors. It is not clear if a single RO frame follows after all active channel frames, or, if a channel-specific RO frame follows each channel, with multiple channels active. I would guess the latter, as the RO follows the measurement processor, which probably follows each channel in succsession.For slow horizontal sweep speeds, where flicker of the analog sweep is visible, the RO portion is multiplexed into the analog sweep, to present flicker-free RO. Obviously, this makes for greater difficulty interpreting effects. The sweep speed transition point is not specified. 1 msec/cm, 10 msec total sweep time, might be on the edge. Perhaps a 5 or 10 kHz test signal should be used, to avoid the possibility of RO multiplexing.Using Chop mode as default will introduce chopping artefacts into each analog sweep with two or more channels active. Chopping should automatically de-activate with only one channel active. Given the nature of the problem we are trying to solve, Chop mode only makes interpretation more difficult. Which portion of the gaps are due to intentional chopping action and which portion of the gaps are due to this problem we are trying to resolve? Alt mode should be used as the default. Reserve Chop mode for slow sweep multi-channel operation, where Alternating sweep makes it difficult to visually compare signals between multiple channels.Here's an idea that is a bit outside of the box: use the M07192 in X-Y mode to display the respective signals from the 2246, and Z axis from the 2246. X from the input to the horizontal output amplifier, Y from the delay line input and Z from the waveform 7B point. Z may need to be capacitively coupled (100 nF), since the signal rides on +5.5 Vdc. This might reveal something interesting, as it eliminates the 2246 Z-axis and Autofocus amplifiers and CRT from the picture.

author: grusus
author_rank: Regular Contributor
timestamp: August 08, 2020, 05:26:55 pm
content: QuoteMaybe U600 is going bad? Maybe it is not registering/interpreting ROB and/or ROR singals correctly. I don't know how warm it should get during normal operation, but compared to U602 and few other chips it is cool/cold.Q1002,3,4 out - no change dots and trace are visible. Q1001 - as expected nothing on screen. No trace nor dots.QuoteHoldoff is adjusted from 0:40-1:03Next video from tripod :-)QuoteDots of readout can be turned off by RO Intensity and also they dissappear with A intensity full CCW.1kHz input to tek:https://photos.app.goo.gl/Z2F68RLn6j6QGcah810kHz input to tek: (look what retrace is doing with holdoff adj)https://photos.app.goo.gl/o95oAKaH9bUMTKE57100kHz input to tek:https://photos.app.goo.gl/CFLUenhDUdnvpadV6QuoteI can't do that. MO7192 has no external z input. tried with X-Y on X on TP 2I and y on 6H. nothing useful - just blurry line. Wen RO intensity is off - line gets thin, no blurr. That led me to do the following:I decided to observe both TP on normal operating mode and RO dots are there:https://photos.app.goo.gl/J3nSnWbewtFwXePEATried to lift RO horizontal and vertical input W804 and R207 - no change.I also tried to lift R215 (Vertical RO enable) - no changeThat means to me, RO dots are inserted elsewhere before TP 2I and 6H and they are not from W804 and R207.One of logical path to me is pin10 of U1001 to Pin 14 of U506. Then to AD mux bus.Second, is that U602 pin20 is reflecting backwards to U602 17 and 18, but - there is no RO From U600...Other thing is that RO enable goes out of U503 also to R502 and then to AD mux bus to U506.There is also RO freeze from U173 to U502, Which need to have proper clock from U606 pin 12 (I don't know freq. it should be) that goes from U501. (I know that they are shift registers but maybe? SR0 are working as those are for attenuators. (U171 and U172) But maybe U173 is making some mess) I know i may be very very wrong, but: it is me trying to understand this circuit :-)

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 09, 2020, 03:43:31 am
content: QuoteRO vertical position ENABLE signals are injected into vertical preamps U210-U240 (column B on sheet 2, R212, R222, R232, R242). They also control output switching of analog muxes U202 and U201.RO vertical position ENABLE signals originate on diagram 9, location 1M, from U2403.But wait, there's more. Look again at analog muxes U201 and U202. The same RO enable signals permit the respective channel vertical position signal to pass on to U280. Vertical signal and vertical signal position are summed before entering the delay line driver.The RO vertical position signal, in through R207 and out through W202, is also summed with the above signals.QuoteThis is very significant, even moreso considering that ROR is disabled and ROB is forced to blank.Note how these dots follow the input sine wave, with a fixed offset. This tells us that the dots are not coming from the RO at all. The artefact is a fault of multiplexing and a DC offset would explain the dots following the input sine wave. The dot effect would correlate to an enable signal and the larger gaps could be caused by a much larger DC offset that drives the beam off screen.Sanity check: adjust channel 1-4 position controls and trace separation control for 0 Vdc at the non-inverting inputs of U203a,b,c,d and U801 (diagram 2). Verify the output of each opamp is also 0 Vdc. No need to make channels 2,3,4 active, leave them off.With 0 Vdc into muxes U201 and U202, check at W202 that there is no DC offset. If a DC offest is observed, lift R201-R204 and R206 one by one until all are disconnected and only W202 remains. Use both DMM and the M07192 for this test.Let's follow this theory down to a conclusion.

author: grusus
author_rank: Regular Contributor
timestamp: August 09, 2020, 01:03:57 pm
content: QuoteDone.QuoteNope. 0VDC on W202.I decided to check W202 with scope.When ch1 horizontal line is on RO dots, on U203A pin1 there is 0V and nothing on siemens scope. But check what is observed when vertical position is off center:https://photos.app.goo.gl/ZWNdsyq39YJp7mNs9I checked all inputs on U202 and this garbage is comming from pin 10. Next I have checked either side of R212. Higher signal was on U2403 side.U2403 side:https://photos.app.goo.gl/z6kWSnJbJYhTMWnt5U600 side:https://photos.app.goo.gl/iTJptGYDSQFsayHv8I decided to desolder U2403 and put it into socket for ease of further removing and inserting.After that, as expected no change - I didn't break anything :-)But when U2403 is removed - no RO artifacts on any channell.There are still cuts in traces.Signal applied: sine 1kHz, 10kHz, 100kHz, 1MHz, 10Mhz.https://photos.app.goo.gl/1taJjj89GxzNGwt17Ok. Now we have signal not interferd by RO. Or maybe not?I am still wondering why I can make dots stop moving by adjusting Scale Ilumination :-).The only logical explanation to me is: When turning SI on, there is very small voltage drop on +15V line (about 0,15V), that can make some change in voltages in calibrator circuit, as it is also connected to +15 V line. Or maybe sth else that is also on +15V line.

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 09, 2020, 02:16:50 pm
content: Good idea to remove U2403. I cut that part just before my last post. Bend pin 1 of U2403 out, to disconnect the enable signal, connect this pin directly to ground and retest.Since U2403 is the source, the real question now: are the bits on address buses A0-A4 correct, implying U2403 has a decoding problem? This is where a logic analyzer would be handy. Or a spare 74HCT374.The hold-off effect observed from about 2:20 to the end is the same as seen on a Tek 2465, very minimal.The retrace blanking on the 2246 is too slow at turn-on. With 1 MHz input to the 2246, use the M07192 to observe waveform 7G, diagram 7. This is the totem pole driver output to the CRT grid. Note the DC levels, relative to ground.QuoteYour conclusion of power supply loading is correct. The measured difference is 1% of the supply rail. An RC oscillator will show a small shift in frequency.For reference, the Tek 24x5 series also exhibit subtle Z-axis dashes in the sweep. The number observed is much higher, probably 50 to 100, with a single cycle of 1 kHz displayed. Intensity has to be set low and even then they are barely visible. Hold-off and RO intensity have no effect, but Focus does. De-focus makes the dashes and gaps a bit easier to observe, they are about 60/40 to 70/30 mark/space ratio. My suspicion is that these are caused by residual ripple in the -HV CRT cathode supply. The mark/space boundary is that of sine wave Z-axis modulation, not square-wave sharp.

author: grusus
author_rank: Regular Contributor
timestamp: August 09, 2020, 03:37:31 pm
content: QuoteIf I bend pin 1 and connect it to ground, behaviour is the same as without that chip, but no Vertical position or trace separation is working.It is not the problem to order one, it is cheap(0,3$) and available. I am just waiting to place bigger order - not only one chip because of shipping cost. I Was thinking also about buying some logic analyzer but are those cheap one for 10-25$ worth anything? I cannot afford now a more costly one for 300-500$ It is more likely for me to buy digital scope like Rigol ds1054Z now - because I will use it more often than a good logic analyzer.Quote15-70V with a intensity fully cw. Always minimum at 15V max varies with A intensity:siemens at 10v/div 2us/divtek has 1 Mhz on input. A intensity at full cwhttps://photos.app.goo.gl/qhVDejdjcqgHJHy28holdoff at min, trigger level in the middle.https://photos.app.goo.gl/ARiA91nBnufZeLLc8QuoteThat's exactly what I thought.I was messing out with scope and noticed maybe sth usefull, maybe not:Look at traces when dots are stopped, and changed to chop mode:https://photos.app.goo.gl/SahrsMDKyyDkFQZGASame on higher sweep:https://photos.app.goo.gl/UpHwK9PyuNujYu2T7

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 09, 2020, 05:05:17 pm
content: QuoteThis behaviour is to be expected and it is good to know the result is the same as removing U2403. What does the sine wave look like?QuoteAdjust A intensity for 40 Volts on the Siemens. What does the 2246 sweep intensity look like?QuoteChopping artefacts are to be expected. Selecting chop mode is incorrect usage, in these tests.Note how intensity grows slowly, in the below cropped image of the 1 MHz sine wave. Sweep is 0.5 usec/cm, intensity change over two cycles implies a rise-time of about 2 us. Set the Siemens to 0.5 usec/cm and show the positive going rise from +15 Volts to +40 Volts. This corresponds to unblanking. Check this with both channels on the Siemens and use the channel that shows the best square wave response. Then change the Siemens triggering to show the fall from +40 Volts, to +15 Volts. This corresponds to blanking for retrace. We are interested in the 10% to 90% transition times and the corner squareness. A faster scope would be preferred.While you are at it, check waveform 7F frequency, to see if this correlates to the slow unblanking and retrace blanking.As for cheap logic analyzers, the Saleae Logic 16 clones are worth the price of admission. Sigrok pulseview supports these and many different LA models and clones.And before I forget (again) thank you for using the tripod.This enables me to see everything as if I am looking over your shoulder.Edit:Here, hold my beer while I do some math:Waveform 7F shows 61 usec per cycle. 18 times 61 usec equals 1.098 msec. Here's the source of the 18 dots we have seen in the 1 kHz sine wave. The rise and fall times sure look like they correlate to the slow blanking and unblanking.

author: grusus
author_rank: Regular Contributor
timestamp: August 09, 2020, 06:49:04 pm
content: QuoteTo me it is the same. No difference if U2403 is removed or in circuit with pin 1 grounded.QuoteBrighter than I will normally use:https://photos.app.goo.gl/kk45TrDJi2WRzuXb8QuoteI know, but you never know when you discover something usefull or interestingQuoteFor reference this is 1MHz square at Siemens input with 50terminator:https://photos.app.goo.gl/EtiShHAnpDesNLx87rising 0,5usec/div:https://photos.app.goo.gl/WXjS7RktxQGy6mZB8rising 0,5usec/div with x5 mode:https://photos.app.goo.gl/sUfjKkuvFup4EHkY9falling 0,5usec/div:https://photos.app.goo.gl/nvuPVcza9xUHS7Eu8falling 0,5usec/div + x5 mode:https://photos.app.goo.gl/P6dtpXHmnM8hgWMP9Quote7F 5usec/div:https://photos.app.goo.gl/cB3RVWCJ1Yag2Suf7and with x5 mode:https://photos.app.goo.gl/tb9PRr9Gt7aSj1Vc7https://photos.app.goo.gl/5xYFjFwnPKSprLtk6QuoteI will check and order one.QuoteNo need to thanks, that was my duty.QuoteBut where is blanking frequency generated? U600?

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 09, 2020, 10:09:02 pm
content: The Z-axis rise and fall times look to be about 0.15 usec and correspond to a bandwidth of 19 MHz.The manual does not specify a risetime for the Z-axis input. Based on what we are seeing, it looks compromised.Refer to the Z-axis response adjustment, paragraph 6 on page 5-5. Check if C2704 can sharpen the waveform, as monitored on the Siemens. The reference square wave looks nice and sharp on the Siemens but without the graticule visible, the risetime cannot be estimated. Some scale illumination would be helpful.QuoteIf you are referring to the A and B sweep blanking signals, U600 is correct. U600 should still be providing blanking control to U602, for A and B sweeps. The RO control inputs to U600 are currently disabled, to eliminate their influence. In turn, U602 pins 17 and 18 control Q1001 and Q1004, respectively. I have lost track of which transistors are currently disconnected. For the moment, just Q1002, to prevent RO blanking pulses.The 18 blanking gaps and dots correlate with the 130 Vac signal (7F) and this appears to be modulating the CRT grid in an unintended manner. It appears that the 130 Vac signal is intended to dynamically alter both the control grid and focus grid bias, in sync. Try disconnecting W1288, to remove the 130 Vac signal.The CRT heater is driven with 6.3 Vac, at the same frequency as the 130 Vac signal, both derived from the main switching power supply. A most unfortunate condition to discover would be a heater to cathode short in the CRT.

author: grusus
author_rank: Regular Contributor
timestamp: August 09, 2020, 11:35:45 pm
content: QuoteMaybe that's because Bandwidth limit is on?So new pics:7G: sec/div same as beforehttps://photos.app.goo.gl/9AthSiuVDTpXaBoc6https://photos.app.goo.gl/pinRxVGvvPTM4nS17https://photos.app.goo.gl/g27jEfNoUz3Zgzfj6https://photos.app.goo.gl/TWPgthTTeew1PdeR67F: sec/div same as beforehttps://photos.app.goo.gl/zuxy8yr7HSFKRg4D6https://photos.app.goo.gl/MDiSfnE7ifpEToVv7https://photos.app.goo.gl/SwCP5SvKuQUbPdrm7QuoteI adjusted that 2-3 weeks ago. Generally I went throu whole adjustment procedure in SM for this scope.Only Q1002 out.QuoteHeater to cathode is 5Min circuit. I will remove CRT tomorrow and check again for sure, but I think there is no short.edit:yes R2267 is making it to be 5.1M diag 11 8MHere is very quick vid because there is no brightness control and I don't want to burn crt, or overload/overheat sth.1kHz sine at input.I don't see dots now in traces but focus is very rough.I am adjusting holdoff during video, and changing base time. Retrace is visible sometimes. Look:https://photos.app.goo.gl/JEvsL4bFySzGxQ6bASo, now I am wondering what does it mean?Will 24mhz 8ch saleae clone be enought, or I should get 16ch version? 8 ch can be delivered in 2 days. 16ch is from aliexpress and it is 2-3 weeks delivery.https://pl.aliexpress.com/item/32780046572.html?spm=a2g0o.productlist.0.0.589a1821tnmNz1&s=p&ad_pvid=2020080918105216458788844781500002479693_1&algo_pvid=7850c058-078d-4625-8d5a-def708b21cdb&algo_expid=7850c058-078d-4625-8d5a-def708b21cdb-0&btsid=0b0a01f815970218528896097ef776&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_And also bandwidth per channel. LA1010 is 16 MHz per ch with 16 ch active. LA1016 is 100MHz per channel witch 16 ch active.

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 11, 2020, 02:23:33 am
content: Had I looked at the -HV supply, I would have known about R2267. It was getting late.Quote5.1 and 11.8 Ohms, not MOhms.QuoteIt means I needed to go to bed and sleep on it.There is a lot going on in this circuit and the 130Vac drive is critical to proper operation as it forms the CRT grid supply. 130 Vac is coupled through C2713, R2722, C2712 and R2721 to CR2701 anode. The negative half cycle forward biases CR2701, establishing a negative charge on C2711. R2724 creates a long discharge time constant with C2711. The positive half cycle, through R2723, forward biases CR2702 which clamps the positive half cycle to the CRT cathode, at -2.7 kVdc. The total negative charge on C2711, as determined by grid bias pot setting, then holds the grid just enough negative wrt the cathode to extinguish the beam.Z-axis signal coupled through C2711 raises the grid voltage closer to the cathode, reducing the grid-to-cathode difference and allows beam current to flow, in proportion to the intensity control setting, which establishes the Z-axis signal amplitude.So the non-uniform sweep intensity, visible retrace, dark spots in the trace and their timing which coincides with the 130 Vac signal, now seem to point to a problem in this area. Either C2711 isn't getting sufficient charge, or its charge is being bled off very quickly.Anticipating the possibility of a defective diode, I have looked into the FDH5004 and find it appears to be an epoxy encapsulated variant of the glass 1N486, which has a Vrrm of 250 V, If_max of 200 mA and Ir_max of 50 nA (all at 25C). This reverse leakage current rating is two orders of magnitude lower than the 5.0 uA of the 1N400x series. BAV21 is a much closer match: Vrrm 250 V, If_max 250 mA and Ir_max of 100 nA.Now for the auto-focus. The 130 Vac signal establishes a negative charge on C2719, in the same manner as for the grid supply. Z-axis signal amplitude modifies the focus grid voltage just the same as the Z-axis modifies the grid voltage. As intensity increases, focus voltage is automatically compensated for the higher beam current. This circuit appears to have no trouble keeping the beam well focused and some part swapping with the grid circuit would certainly be appropriate.Something else I would like to see beforehand are the Z-axis waveforms 7B and 7G, simultaneously on the Siemens. My interest is in comparing the squareness in and out, to see if this Z-axis driver amplifier has suffered a loss of bandwidth.Which reminds me, the 20 MHz BW Limit only affects the vertical amplifier.QuoteYes, until the day arrives where more channels and higher sampling rate are needed. Anticipating the arrival of that day, the LA1016 would be a wiser choice.

author: grusus
author_rank: Regular Contributor
timestamp: August 11, 2020, 01:53:19 pm
content: QuoteIn Poland it Was late too. Why I saw 5M?Also Heater to cathode is not 5M It is approx 1K. Wrong wires.QuoteGood idea :-)QuoteI was considering changing all hv caps while changing all electrolytics but they are rated at 4kV. I found in Poland only 3kV caps and they are ceramic disc caps. Thats why I decided to leave them as is. I will search for propper caps and buy them. Also I can use 4,7n +4,7n in parallel, or 6,8n+3,3n. Those are 4kV ceramic capacitors.Other thing - 130VAC in my case is 122.QuoteIn my scope CCR2701-4 were 1N4936 - as I have them in stock, I changed them today, because it will be hard to tell if diode is leaking. No change of behaviour.Quote1k at input of tek:7b - top7G - bottom.https://photos.app.goo.gl/j37oHN2hKdWLuKYy91M at input of tek. (siemens at 0,5usec/div)https://photos.app.goo.gl/7ZCWdonNjsvY1a529x5https://photos.app.goo.gl/bkK4MJtaapHRbsUM6https://photos.app.goo.gl/bUKrFjhcdiRo7Anf7x5https://photos.app.goo.gl/JkY9rnnUMWUcUmD67QuoteThat should be obvious to me.QuoteLA1016 ordered.

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 12, 2020, 01:18:45 am
content: Both input and output rise and fall do not look at all good. The rounded leading edge of the Z-axis output flat top corresponds to beam turn-on and should be just as sharp as the initial corner of the rise from zero.For ease of comparison, let's see the 1 MHz square wave against the Z-axis input signal. Then repeat with Z-axis output signal. Raise the sweep speed so the initial rise (with positive trigger) spans at least 1 division, preferably 2 divisions. Then change to negative trigger and show the falling edge. No need to use 5X magnification.Align both signals at -2,5 divisions below center, adjust vertical setting and variable gain to place the tops of both signals at +2,5 divisions. This will make the 10% and 90% points coincide with -2 and +2 divisions and simplify rise & fall time measurement.The overlaid signals will help quantify the M07192 limited rise time against the Z-axis measurement. If it is possible to borrow another 100 MHz scope, that would be very beneficial.

author: grusus
author_rank: Regular Contributor
timestamp: August 12, 2020, 12:29:18 pm
content: QuoteI was also worried about it.QuoteSignal from 7B and 7G is not 1MHz. It is more like 200kHz.1MHz at tek input.200kHz at MO7192 CH2.7B:0,5us/div:https://photos.app.goo.gl/9zBqwyRtfkPPw93Z7https://photos.app.goo.gl/rRPBCxsnHYK3q4VR60,2us/div:https://photos.app.goo.gl/SHuZy453kDsG1scLAhttps://photos.app.goo.gl/NxoWEMRb3WScsvXU67G:0,5us/div:https://photos.app.goo.gl/c9bfUHgRmowsJMrW8https://photos.app.goo.gl/iyjUcUWepYuyEUYn90,2us/div:https://photos.app.goo.gl/4VScVo2CbXrrGoA9Ahttps://photos.app.goo.gl/ccxEv4YrxhhqcZhj7QuoteI will call my friend, if he doesn't need it I will borrow it.///Edit: He will be back from holiday on sunday, so I can get it on monday. He said: no borrow time limit.Just another thing that may or may not be usefull:When I hit single sequence trigger button, trace is also cutted.quick video: 1kHz input sine.https://photos.app.goo.gl/AS2VQWPp2f1RRpVUA

author: rf+tech
author_rank: Frequent Contributor
timestamp: August 12, 2020, 10:03:08 pm
content: I'm reading both transitions as about 60 ns, no difference input to output.Move back one stage and show Q1001 emitter against square wave. 0.2 us/div and 0.1 us/div, for better resolution. Move the horizontal position just far enough to align the rising 10% point on the center vertical line, or, the rising 90% point. This useful technique makes reading the 10-90 difference a bit easier.Once the setup is complete and a photo is taken, turn off the 2246 and allow it to cool down completely. There were some videos early on that showed a gradual change in the beam intensity over the first few seconds, when the 2246 was first turned on. After an hour or so, with the camera ready, capture the M07192 display when the 2246 is first turned on.Bandwidth and rise time are inter-related, for analog scopes Tr(ns) = 0.35(1/BW). So 60 ns = 5.8 MHz, seriously degraded. Z-axis rise time does not appear as a specification, rather Tek makes reference to "usable bandwidth." The 465 (100 MHz, 3,5 ns Tr) states 50 MHz. Both 2445 and 2465 state 20 MHz. Using 20 MHz as a lower BW limit, Tr = 17.5 ns and for 50 MHz as an upper BW limit, Tr = 7 ns.Refer to TM page 1-9 "External Z-axis Input" specs, use the 200kHz square wave to verify both thresholds. Then set the square wave amplitude for 5 Volts into both Z and channel 1 (cable from gen to tee at Z, then to ch 1 with terminator).With the M07192, show the square wave into rear panel Z input on one channel and 7B on the other channel. Same setup with overlaid traces, -2.5 div to +2.5 div.QuoteNotice there are 16 gaps per 1 ms cycle. The gaps repeat with a period of 62.5 us, which coincides with the scope's inverter power supply.

author: grusus
author_rank: Regular Contributor
timestamp: August 13, 2020, 09:08:30 pm
content: QuoteAll at 0,2us/div - this max on MO7192https://photos.app.goo.gl/vTMQi7RhVtaWKyHt6https://photos.app.goo.gl/JYa3B35ts5nUs2Gw9QuoteAfter 2 h:https://photos.app.goo.gl/5pix8S9gYjGDXhXG7Starting point is 0,5us/div to see both rising and falling edge.QuoteZ behaves as in specs but with terminator removed. Otherwise voltages must be +40% - +50% +/-https://photos.app.goo.gl/rVPQimrAS5bR95Cg7https://photos.app.goo.gl/6vGAyRCpqYVBYfSQ8QuoteI decided to look at +130V ac and it looks like this:5V/div x10 probe 20us/div:https://photos.app.goo.gl/C3mpCW2Ne48GDrcL6I was thinking if maybe PSU is failing.

author: grusus
author_rank: Regular Contributor
timestamp: October 05, 2025, 06:19:04 pm
content: Hi all.Long time passed and I decided to look at this scope again. It turned out that R2718 was 100K instead of 75ohm. Swapped. Issue no longer occurs. Thank you all for your help!