Tektronix 465 w/ DM44 subject to whims. - Page 1
Forum section: electronics / repair

author: Malefoda
author_rank: Contributor
timestamp: September 04, 2017, 08:55:36 pm
content: Hello,I'm new to this board and have been advised to come here by the DIYAudio fellows about my Tek scope. I'm also happy to watch these videos of DaveI'm no engineer but can learn, years ago I had no idea what a resistors was and here I am making simple circuits and using a scope and signal generator =)The 465 has been given free to me with the "stopped working" note. First I've put the main selector to 230V, then powered on. All lights on but no trace at all.Tried it some more times and one day, all of a sudden, it worked!I've used it a couple of days, even powered it just to let it warm sometimes. Once power off made a bright flash on screen, almost painfull to see and also like a static discharge noise on startup. But tonight here it goes again, no trace at all. Seems the fan is on a very slow speed also.Several threads, the service manual but it looks too big for me... What about a first control by sight with case removed, maybe pictures? Or some of you with already some ideas?And I wonder why I don't have the lovely knob on the delay pot...Thanks!Matthieu

author: tautech
author_rank: Super Contributor
timestamp: September 04, 2017, 10:05:41 pm
content: Welcome to the forum.Link the SM so we can all be on the same page as you are.Grab this Tek doc too, it gives good basic guidance:http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdfStudy the SM, really study it....pull the case off and get to the point where you know where things that are mentioned in the SM actually physically are. Take your time and become familiar with it's guts and mark test points if they aren't identified.Common failure points for CRO's are the EHT circuitry for the CRT, the LV supplies and occasionally the PDA.Start with checking the basics, the low voltage PSU rails. They must be to spec as outlined in the SM.Others that are more familiar with the 465 will likely chime in with good advice too.Good luck with your 465.

author: tggzzz
author_rank: Super Contributor
timestamp: September 04, 2017, 10:09:41 pm
content: Measure the voltage and ripple on all the PSU rails, compare with the values in the service manual.Expect to find electrolytic capacitors which have "dried out" and need replacing. Typical symptom: too much ripple.Expect to find tantalum capacitors which have gone short-circuit and need replacing.Expect to find oxide on pots/switches which needs removing by repeated operation and/or fluff removal and/or IPA/Caig Deoxcit. Typical symptom: noisy operation and/or only some ranges work.Beware of the high voltages and find where they are; some are dangerous.There are many threads on this forum about those topics.

author: barry14
author_rank: Regular Contributor
timestamp: September 04, 2017, 10:38:19 pm
content: I can't help with your problem but I can answer your question about the delay knob. It is not a calibrated 10 turn knob because the delay time is read out on the digital display of the DM44. You should consult the manual for details.

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: September 05, 2017, 04:13:50 am
content: If you look through 1861-1A to 1861-5 of the Tek465 service manual on Electrotanya, there's a very thorough troubleshooting procedure for this sort of display problem. Like you, I'm far from expert on this stuff. But I have fixed my Tek485 power supply and HV circuit a few times with help from forum members. I had to do a lot of research and reading before I was game to probe into the HV end of the power supply - there's dangerous voltages in there, as others have noted. If you follow the manual, you'll quickly encounter a step requiring testing of the -2450V supply. I'd try to exhaust all other possibilities on the low voltage side before even thinking about probing the HV side, which carries considerably higher risks.As suggested by tautech, you will need to spend quite some time working out where your low and high voltages are so you know what you're probing at and also studying the schematics and theory of operation in the service manual. I have found it useful to read and re-read them repeatedly as my understanding improves. There's also much useful reading here and elsewhere about good and bad practice when working in and around power supplies - they're worth investing time in as well. Good bedtime reading...

author: Malefoda
author_rank: Contributor
timestamp: September 05, 2017, 06:37:44 am
content: Thanks all,ok will do my homework and have in mind that kid must be away as there is potential danger and the fact I'll do it in the kitchen. And need to borrow a second scope when it's ripple time.Will use the Tek465 service manual on Electrotanyahttps://elektrotanya.com/tektronix_465_oscilloscope_full_sm.pdf/download.html, thanks Lorenzo_1, (I have no B on my serial, is that ok?...and can't even figure out what is the 1861-1A refers to... see how bad I am ?) and I'll let you know my findings. My, lots of work!

author: tggzzz
author_rank: Super Contributor
timestamp: September 05, 2017, 06:58:31 am
content: Quote from: Malefoda on September 05, 2017, 06:37:44 amPersonally, I wouldn't. Consider that cooking in a kitchen produces aerosols of whatever you are cooking. The droplets are small and hang in the air for a long time. These droplets will eventually stick to nearby surfaces.When you look at the scope internals, you will see that many switches (e.g. vertical sensitivity and timebases) are exposed finger contacts. When they get dirty they can becarefullycleaned in such a way the fingers aren't damaged. And then there is the problem of films on sensitive front ends etc.My attitude with my daughter was to encourage her to stick her head into things that I was doing. She could see me thinking about what might hurt me and then taking precautions to avoid problems. To give her a clue about electricity, I took her into the country and found an small moveable electric fence. After testing it myself, I told her to lightly touch the back of her fingers to the fence - and why not to grasp it or touch it with the inside of her grip.Later on she became a solo glider pilot before she could start to learn to drive, and self-funded a 6 month trip to the antipodes between school and university. Exposing her to calculated dangers worked well.QuoteStart by using a multimeter on AC ranges.

author: Malefoda
author_rank: Contributor
timestamp: September 05, 2017, 12:05:23 pm
content: Quote from: tautechWell, in fact there is no choice, opened the beast and almost wanted to cry, that's no mere alarm clock! With no clue of what to look for that was useless. RTFM definitely, but at least I saw TPs are written down on PCBs.Quote from: tggzzzSo is this how you call Brexit, calculated dangers?just kidding!

author: tggzzz
author_rank: Super Contributor
timestamp: September 05, 2017, 03:41:13 pm
content: Quote from: Malefoda on September 05, 2017, 12:05:23 pmKnown and unacceptable dangers. But since this isn't a political forum, I'll say no more on that topic.

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: September 05, 2017, 10:38:59 pm
content: 1861-1 is a page number in the manual. Go to page 243 of the PDF file or thereabouts and you'll find it. Can't help you with SN question. Note that the Electrotanya manual specifies applicable numbers on it's title page.

author: tggzzz
author_rank: Super Contributor
timestamp: September 05, 2017, 10:54:16 pm
content: Quote from: Malefoda on September 05, 2017, 12:05:23 pmTake it slowly, start with the section on faultfinding PSU problems. There's no point in looking elsewhere until all the power rails are correct.

author: Malefoda
author_rank: Contributor
timestamp: September 07, 2017, 11:56:51 am
content: Hello,the most probable you predicted was right. I am amazed on how it managed to work with such supplies few days ago...I need to change all the filter capacitors, 5 big caps with odd finger shape, need time to spend finding cheap and suitable ones.

author: tggzzz
author_rank: Super Contributor
timestamp: September 07, 2017, 12:12:33 pm
content: Quote from: Malefoda on September 07, 2017, 11:56:51 amIt can be difficult to remove those without damaging the PCB tracks. Some of the through-plate holes are used to connect different sections of tracks, as is the cap's can. Hence you should ensure that you add new bridging wires where necessary.Caps with those leads are difficult and expensive to find. The usual technique is to use a modern capacitor, with similar capacitance, significantly higher voltage rating (to reduce the ESR), a high temperature rating and specified for SMPS operation (i.e not 50/100Hz!) for reliability. Then either create your own PCB for converting from 2-pin to 5-pin, or just bodge them in somehow.See other posts for more details.

author: Malefoda
author_rank: Contributor
timestamp: September 07, 2017, 12:31:55 pm
content: Ok thanks!No more answer notifications but I just wanted to add that C1512 has already been changed, a tiny blue cap on which I can't read any brand. But they'll all go to the trash bin if too expensive, else that'll be the scope's place sadly.

author: tggzzz
author_rank: Super Contributor
timestamp: September 07, 2017, 12:53:33 pm
content: Quote from: Malefoda on September 07, 2017, 12:31:55 pmModern caps are surprisingly cheap.It would be unnecessary to bin the scope - much better to advertise it on ebay stating its known problems. You would be surprised how much people will pay!

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: September 07, 2017, 01:58:29 pm
content: Quote from: Malefoda on September 07, 2017, 12:31:55 pmC1512 is across the 55v to 120v tx output via rectifier CR1511. Its stated capacity on the schematic is 550uF and I would expect it to be rated at least for 100v. Modern caps are fairly small, but I would not expect it to be tiny!With the output voltages that low across the board, I would imagine that at least one of those smoothing capacitors (C1512, C1513, C1542, C1552, C1562) is dragging the TX output down quite badly. What are you getting at 120v unreg?I would check all capacitors on the atached which are marked in red. The one at the top left of the picture is under the metal shield. High voltages exist under this. Make sure evreything is powered off before removing that shield. Replace it imediately afterwards. Some of the indicated capacitor on the top of the PCB may be wet tantalum types. These tend to dry out an short over a long time. They might also be electrolytics so wowrth checking anyway. There will also be a handfull of blue bead types in the same general area between the big cans (which are underneath) and the metal shield and to the rear. These are dry tantalum capacitors and as someone has already mentioned, these should also be checked as short out when they fail.As you have discovered, there is quite a lot going on underneath the hood and it can seem overwhelming. For now, just focus on the power supply section. If I might also point out, a number of parts protrude from the PCB at the sides and can easily be caught and damaged when removing or replacing the case so care needs to be taken to avoid damaging anything.

author: Malefoda
author_rank: Contributor
timestamp: September 08, 2017, 08:40:57 am
content: Hello gents,as for caps I've chosen that series:http://uk.rs-online.com/web/p/condensateurs-aluminium/7441253/For the new checks I've updated measurements with the 120V.For on-boards highlighted caps I can only check for shorts (AFAIK with my DMM), none is shorted, they range from several kto 77(C1220) depending on which cap in the circuit. My tantalum caps are red ones, many having like a rubber/hard-yellow-thing o-ring on leads. No Short is the only thing I can say.Here is a picture of my Interface Board, dated 1971. (A big one, so I've linked the image instead of insterting it).http://atsh.free.fr/temp/Tek465%20Interface%20Board.JPGRight now I stick on saving a bit to afford caps, I want to keep it and sell my ugly Wavetek 9020.

author: Malefoda
author_rank: Contributor
timestamp: September 09, 2017, 05:22:05 pm
content: Removed the caps today, all but easy.Pads at the already replaced one are loose and I must admit I did lift one. Pictures were done to link ground where needed for there will be no more 4 legged caps.I managed to get all the caps for 22€ shipped, bearable for me.C1512, not tiny in fact (my english left to be desired sometimes, sorry) but at least smaller than OEM and even of lower capacitance! Looks like general purpose from BC.

author: bd139
author_rank: Super Contributor
timestamp: September 09, 2017, 06:10:52 pm
content: Keep that wavetek one. You'll need it to fix the Tek one every time it goes wrong. If it's a derivative of the OS9020 they are not terrible scopes.Those BC caps are nice.With respect to the rail voltages, there are a couple of smaller electrolytic/tantalum ones on the interface board on the 55v rail after the regulator. I tend to desolder each of them in turn and see if the situation improves. Then the tants on the horizontal and vertical board. The entire scope's voltages are derived from the 55v rail if I remember correctly.I'm praying that the EHT multiplier isn't dead or you're SOL without a donor scope and about 5 hours of work.I've given up on old teks myself. Have fixed several 4xx units.

author: Malefoda
author_rank: Contributor
timestamp: September 09, 2017, 06:50:10 pm
content: Not very encouragingThe Wavetek is a rebranded Beckman Industrial 9020, never planned to have 2 scopes but if the Tek 465 is not reliable it's not going to stay.Drum roll until I put new caps in. Hope it's not wasted money!

author: bd139
author_rank: Super Contributor
timestamp: September 09, 2017, 07:24:09 pm
content: I've fixed worse ones believe me. Fingers crossed for you

author: tggzzz
author_rank: Super Contributor
timestamp: September 09, 2017, 07:27:57 pm
content: Quote from: Malefoda on September 09, 2017, 06:50:10 pmDon't be unnecessarily discouragedIMNSHO an analogue Tek beats most other analogue scopes.OTOH, I'm not a fan of the DM44. While it works, it is complicated kludge due to of the technologies of the time. But, provided the knob works, they can be ignored.

author: bd139
author_rank: Super Contributor
timestamp: September 09, 2017, 08:32:34 pm
content: Yes particularly my Hp1740A which has decided to stop sweeping this afternoon. Just after I sold the bloody rigol one too.This is the analogue scope ownership experience. A good education however!

author: Malefoda
author_rank: Contributor
timestamp: September 09, 2017, 09:29:51 pm
content: Seems owning oscilloscope is a hobby by itslefWhen I see parts cost, resell price of the 465 and the Wavetek I can get a fully working Tek 2236 and troubles away... and some money left! But then QED, oscilloscope itself becomes a hobby!

author: tggzzz
author_rank: Super Contributor
timestamp: September 09, 2017, 09:54:02 pm
content: Quote from: bd139 on September 09, 2017, 08:32:34 pmThe problem I had on mine was that a PCB track had been abraded.On the timebase board the rotary timebase switch has a black plastic cover a couple of inches in diameter and with the "spear" from the front panel going through it. After removing the PCB, the black covers (one each side) can be removed after removing a springclip. Make sure you don't lose any of the gold finger connectors in the covers.Examine the PCB tracks on the board where the edge of the covers rotates and touches them - and abrades them. The fix is simple: solder a single strand wire across the break, making sure no solder spreads onto the gold PCB switch contacts.

author: bd139
author_rank: Super Contributor
timestamp: September 09, 2017, 10:51:46 pm
content: Oscilloscope ownership is a hobby. I might have finished building my transceiver if I didn't have so many scopes. It's like working in a kindergarten cleaning up sick all day.I'll start another thread on the 1740A. Rather than the switches causing trouble here it looks like the trigger is deceased. I can single sweep at any time base setting. Auto/norm have died. Hope it's not a pesky hybrid.

author: tggzzz
author_rank: Super Contributor
timestamp: September 09, 2017, 11:10:13 pm
content: Quote from: bd139 on September 09, 2017, 10:51:46 pmOh, but you love them all, really.QuoteThere are existing threads. I'd bet on something simple, maybe a switch, maybe a bias pot. In a 485 I had a resistor subtly fail in a trigger circuit; thatwasa pain to isolate but an easy fix.

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: September 10, 2017, 09:56:36 pm
content: Quote from: Malefoda on September 08, 2017, 08:40:57 amAt 77that is a very low reading for C1220 and I would suspect it of being leaky. I would de-solder or snip one end and check it again. If the reading is still that low then it needs replacing. But I would also expect R1220 (22.1ohms) to get rather hot as a result. You might want to check that it has not gone OC.Coming back to your line voltages, it is interesting to note that your unreg line is 131v but the 55v line which is derived from a tap on the same TX winding is low. As was mentioned by db139, the 55v line is used to provide an appropriate reference voltage via a resistor divider to the op amp in each of the +15v, +5v and -8v lines. If the +55v input is low, then the voltages output on these other lines will be affected. Your measurements show that the +55v line is at 40.0v hence 72% of the expected. A quick calculation shows that +15v, +5v are exactly proportionally affected and the -8v nearly so. For the +110v line the arrangement is a little different, but that +55v is also used as a reference via VR1515 (56v) which when added provides a regulated +110v (55+56 = 111, then you also have a -0.7v drop across CR1514).So I think it is necessary to establish why the +55v line is low.I would suggest we first see how the replacement of the caps you have purchased goes, in particular whether replacement of C1513 makes a difference. If the line is still low after that, then the other cap to bear in mind is C1534 but you only need to de-solder one end of that and if the voltage has returned to +55v you know that it was responsible.If we get to that point and the line is still low, then we need to start checking the voltages marked at the various reference points on the circuit around U1542A, Q1532, Q1534 and R1538 to see what we get.But first let us know how your cap replacement went.

author: Malefoda
author_rank: Contributor
timestamp: September 14, 2017, 06:12:59 pm
content: Quote from: WaveyDipoleNot that bad, just needed less than 10mm long extender on the 300mm diameter caps. Linked the grounds when needed.Power lead on... power and no smoke!All supplies are OK, no more ripple my DMM can find, a rock solid 55.00V, the only measurement out of spec is the 110V at 114.5V when max allowed is 113.4V. Still some work?Thank you for the helping hands, it's back from the deadBTW, off board C1220 is good.The scope never really worked prior to this repair but as it seems birghter now, is the trace flashing in a centered position on power-off normal?

author: bd139
author_rank: Super Contributor
timestamp: September 14, 2017, 06:48:17 pm
content: Excellent. Nice work

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: September 17, 2017, 10:58:40 pm
content: Quote from: Malefoda on September 14, 2017, 06:12:59 pmGreat to see it working.Quote from: Malefoda on September 14, 2017, 06:12:59 pmWell, that's not too far out of spec so it will probably not be much of a problem for the present, but if you want to put your mind at rest then you could try checking checking resistors R1516, R1517, R1518, R1519 in case they have drifted significantly from their values and replace any that are out of tolerance. Also check whether either Q1516 or Q1518 are leaky. Finally, the voltage at the collector of Q1518 should not be exceeding +112v. If it is, then try replacing the 56v zenner, VR1515, which was the cause of a similar problem on mine.Quote from: Malefoda on September 14, 2017, 06:12:59 pmI checked on mine and it would seem that it is not unusual to sometimes get a brief flash of the fading trace on power off, although it does not seem to happen every time. Often the trace will just fade away and disappear without a flash.

author: Malefoda
author_rank: Contributor
timestamp: September 20, 2017, 06:37:22 am
content: Quote from: WaveyDipoleOk I keep that for the next time I'll need to open it or for long cold winter night's bore, right now I can go with it