Tektronix 7633 Scope, Can anyone please help Old64goat!!! - Page 1
Forum section: electronics / testgear

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 12:06:20 am
content: My friend Old64goat is having a problem with a Tektronix 7633 Scope that he won at a auction!!!No Trace, No High Voltage?He explains the issues here in his videos:1.2.Brace yourself, he calls himself The Blind Tinkerer!!! Might take some getting used too, but he has a heart of gold and would help anyone out.Thank you for any help you can give him!!!

author: KWKolb
author_rank: Contributor
timestamp: May 02, 2017, 12:35:15 am
content: You can remove the back panel, transformer, and rectifier/filter assembly as a group by removing three Phillips screws on the left and right sides of the chassis (six screws total).The assembly will slide out the back. There should be sufficient slack in the cables, but I had to disconnect one or two on my 7633.Good luck and please keep us informed.Kevin

author: Electro Detective
author_rank: Super Contributor
timestamp: May 02, 2017, 04:58:41 am
content: Old64goat YT videos rock! especially before he sold the shop.Hope he sorts it out asap, good luck and best wishes to him.Watch out for DRY contacts in the switches on these old school Teks, before getting too medieval.If enough of them are just not making it, the symptoms can be identical to the usual suspects PSUs, caps etcand he could be facing an unnecessary troubleshoot merry go round

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 11:33:59 am
content: Thank you Kevin,for sharing your wisdom and helping the Old64goat out!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 11:35:46 am
content: WOW, thank you great advice.Thank you for sharing your wisdom helping the Old64goat out!!!

author: Harb
author_rank: Regular Contributor
timestamp: May 02, 2017, 11:37:49 am
content: Pity the old bugga can't see better.....must be a pain in the but having to use a magnifying glass to look at everything

author: KWKolb
author_rank: Contributor
timestamp: May 02, 2017, 11:59:12 am
content: Picture of the rectifier/filter assembly when slid out. Mine is awaiting a recap.

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 01:53:05 pm
content: Thanks everyone for helping this kind gentleman out!!!He is having a problem with registering, so he sent me this message to post to everyone, this is what Old63goat wants me to share with you:"If you would do me a favor and mention to them that ALL 5 of the fuses are good, ALL the low voltages are good.However I am not getting the minus 1,475 volts at the HV test point, all I get is ONE volt positive at that HV test point.Also I was able to slide out the low voltage power supply BUT I can't get the HV "box" out, the one that has that -1,475 volt test point on it."Thanks everyone!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 03:27:58 pm
content: Fantastic picture, keep them coming!!!Thank you for sharing!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 03:45:31 pm
content: Thank you for helping this kind fellow out.

author: David Hess
author_rank: Super Contributor
timestamp: May 02, 2017, 04:18:06 pm
content: These oscilloscopes are very repairable however the 7633 is the most complicated of the 76xx series and finding faults may require an electronics engineer's ability to understand the schematics. The failure is probably simple if you can find it.I am puzzled that you saw the CRT heater operating but measured no cathode voltage. The CRT heater supply comes from the high voltage inverter so usually both are present or neither are present.The high voltage connector for the PDA (post deflection acceleration) pulls straight apart. You might have to twist it a little bit if it sticks do to friction. But there is no reason to test the PDA voltage because the CRT will work *without* the PDA connected and without any PDA voltage although the CRT will be dim, poorly focused, and have the wrong deflection.The exposed tip of the PDA connector is the CRT side so there is no high voltage there when it is disconnected.Tektronix did not use security screws. Your magnified views show stripped Philips heads which is a common problem. I use small vice grips to remove them and then replace them with appropriate machine screws.The low voltage test points are exposed on the opposite side of the PDA connector or they can be accessed from the rear after the cover is removed. Page 4-9 and 5-32 discusses them and figure 8-17 at the back of the manual shows where they are on the z-axis board.The 7A26 is a 200 MHz dual trace vertical amplifier and operates at 100 MHz in the 7633. It is nicer than the 100 MHz 7A18 (75 MHz in the 7633) which would normally be installed into the 7633 because it has the switchable 20 MHz bandwidth limit.How do you know that the 7B53A timebase works? You might swap it with one of the 7A26 vertical amplifier to see if that unblanks the beam. The beam is only unblanked when a working timebase or vertical amplifier plug-in is installed into the horizontal (right most) slot. A vertical amplifier would normally be installed into the horizontal slot for X-Y operation although the 7B53A timebase also supports this.I think you will have to gain access to high voltage board A10 for measurements but I am not sure how to do that. The oscilloscope will operate without the readout board installed which may help. There is a test point for the z-axis output which I would take a close look at. If the CRT is unblanked, then the intensity control should change the voltage level there.The long cover in front of the PDA connector is just the CRT cover. There is nothing under it except for the CRT.

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 04:51:40 pm
content: David,WOW, thank you for all that detail.

author: casinada
author_rank: Frequent Contributor
timestamp: May 02, 2017, 05:00:38 pm
content: In his videos he mentions the User manual. Does he have the service manual?http://exodus.poly.edu/~kurt/manuals/manuals/Tektronix/TEK%207633%20%20Service.pdf

author: David Hess
author_rank: Super Contributor
timestamp: May 02, 2017, 05:56:10 pm
content: The available free scans of the 7633 service manual are actually pretty good and the one casinada linked is the one I have.1. If the -1475 cathode voltage is missing, then check that Q1195 is good, capacitor C1198 is good, and that unregulated +15 volts is present across C1198; these are all shown in the upper left corner of schematic 7. Fuse F814 located on the rectifier board and shown on the left side of schematic 8 supplies the unregulated +15 volts to the high voltage board but I think Old64goat checked it.I know this means gaining access to the high voltage board but what are you going to do? Unfortunately, I am not sure how to do that. Someone else here are on the TekScopes@yahoogroups.com email list should know.2. When you pull the reduced scan switch out on the front which I saw Old64goat messing with, then the -1475 cathode voltage is doubled to about -3000 volts while the PDA voltage stays the same. This reduces the CRT deflection to 1/2 of its normal value and makes the display sharper and brighter. This function makes the high voltage circuits more complicated on the 7633 than the 7623A which lacks this function.3. Once the high voltage is working and if there is still no display, monitor the output of the z-axis amplifier to see if the beam is being unblanked and if the intensity control is working. There is a procedure in the service manual for adjusting the transient response of the z-axis amplifier which describes how to monitor this signal.4. That readout board we see in the video is one of the later analog/digital hybrid readout boards and produces the second best display in my opinion. (1) The earlier boards used analog (!) ROMs and the hybrid board replaced them with a digital ROM so this 7633 is one of the later ones. The service manual casinada linked only shows the earlier all analog readout board but that should not matter for this. For those who are interested, the details of this hybrid analog/digital readout board can be found in the 7904A service manual.(1) There is *another* hybrid analog/digital version which is even better (or at least as good) but this one is pretty good. My favorite 2232 use a similar character generation method and looks great. Vector is always better than raster.

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 07:17:41 pm
content: Quote from: casinada on May 02, 2017, 05:00:38 pmCasinada,I will send it to him.Thank you for sharing that link!!!Yes he has this manual now.Thanks again!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 07:24:24 pm
content: Quote from: David Hess on May 02, 2017, 05:56:10 pmHi David,Old64goat is going to make another video to provide more information after reading your post, that you so kindly provided!!!Thank you for trying to help him, he is a very nice person just trying to get his vintage electronics repair shop up and running again!!!Thanks again!!!

author: dave_k
author_rank: Frequent Contributor
timestamp: May 02, 2017, 07:36:20 pm
content: In his first video, he says the pilot light for the main power light is not working. This might indicate a short to ground on the 5v supply rail. I had a similar fault in a 7603 scope, which was traced to a shorted cap on the main interface PCB.

author: james_s
author_rank: Super Contributor
timestamp: May 02, 2017, 07:48:17 pm
content: Does this use a voltage multiplier to generate the high voltage? I've seen shorted capacitors in those cause a lack of HV while not greatly affecting lower voltages coming off the same transformer.

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 08:20:06 pm
content: David,Here is the video he made for you:Video For The EEVblog Forum -Thank you David for all your help!!!Everyone please leave feedback on his video also, so he can respond to you faster!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 08:22:03 pm
content: Quote from: dave_k on May 02, 2017, 07:36:20 pmThank you for helping him. Please see his latest video!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 08:24:02 pm
content: Quote from: james_s on May 02, 2017, 07:48:17 pmGreat question, could you please see his latest video and ask that same question again.Thanks again!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 02, 2017, 09:15:54 pm
content: Question,What type of High Voltage Probe does the old64goat need to troubleshoot his scope?I think we need some urgent help with this one to keep him safe:)

author: tautech
author_rank: Super Contributor
timestamp: May 02, 2017, 11:21:50 pm
content: Quote from: finom1 on May 02, 2017, 09:15:54 pmOnly a DMM capable of measuring the EHT, the voltage will be listed in the SM and you want a little V headroom.Be aware the EHT voltage is for the CRT cathode and it is negative and commonly in the 1.5 - 2.5kV range. Check the SM.I use old AVO's for this as they have a 2.5 or 3kV range, depending on the model.Assume the PDA is working until proven otherwise, it can be +10kV and tricky to measure without a UHV probe.PDA multipliers do fail but it is rare, for now assume it works.

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 12:37:04 am
content: Can someone please provide screen shots or pdf scans of what the old64goat is asking for?Here is what he has written:"This PDF is driving me nuts, I can't find anything on it.David posted this answer on his latest post:"1. If the -1475 cathode voltage is missing, then check that Q1195 is good, capacitor C1198 is good, and that unregulated +15 volts is present across C1198; these are all shown in the upper left corner of schematic 7. Fuse F814 located on the rectifier board and shown on the left side of schematic 8 supplies the unregulated +15 volts to the high voltage board but I think Old64goat checked it."Where is schematic 7?I can't find schematic 8, ALL fuses test good.As I had mentioned in the newest video I am getting all the low voltages on that connector(disconnected) from the Z-AXIS board.If there are other low voltage test points I can't find them.What may help is a print out of all the schematics & voltage test points for this no HV problem.Maybe you can post this for me.Thanks,Bill"Please help provide these documents to help solve his problem if you can. He is very thankful for all the help he is getting!!!

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2017, 12:52:37 am
content: Going to roughly respond to the video in order:1. It looks like the triggering is working. The internal trigger on these oscilloscopes is pretty complicated because the mainframe selects from the left or right trigger sources and the dual trace plug-ins select from their channel 1 or channel 2 sources; that makes 4 internal trigger sources so it is easy to have it configured in a way that it seems like it is not working.2. It looks like the power lamp is burned out. It runs on the +5 volt regulated output but since the triggering apparently works, we know the +5 volts is working so the lamp is probably just burned out.3. The transistors on the horizontal CRT amplifier board run hot; I cannot hold my finger on them when they are operating. I verified this on my 7603 which is a very similar design. The load resistors run hot also; that is why they are so large.3. I figured out the mystery of the CRT heater being active while the high voltage is apparently missing.The heater for the CRT electron gun is toward the back of the CRT and not easily visible. What Old64goat saw is the flood gun heater which is used on storage CRTs to "flood" the screen with electrons as part of the storage capability. You can tell because the flood gun heater that you see is below the horizontal deflection plates and the electron CRT gun is toward the back of the CRT before any of the deflection plates. The flood gun heater runs off of the -15 volt supply through an 8 ohm as shown on schematic 10 and will be powered whether the high voltage inverter is operating or not.4. So that means that the high voltage inverter which supplies the electron gun heater, -1475 cathode voltage, and PDA voltage is not operating. That leads back to checking Q1195, capacitor C1198, and that the unregulated +15 volt supply is present across C1198. If those are all good, then the high voltage regulation loop needs to be checked.Quote from: dave_k on May 02, 2017, 07:36:20 pmThe triggering works and Old64goat verified the presence of the +5 volt regulated output at the test point.Quote from: james_s on May 02, 2017, 07:48:17 pmThe high voltage multiplier for the PDA is separate from the cathode voltage rectifier but they share a winding. It is possible that the high voltage multiplier is shorted but I am not sure what result that would produce. I suspect it would blow fuse F814. If fuse F814 is good, then we should still see *something* at the negative cathode voltage test point if the inverter is operating.Quote from: finom1 on May 02, 2017, 09:15:54 pmHis VTV works to 1500 volts which is good enough for checking the cathode voltage and that is all that is needed at this point. I have a Fluke 40k-6 which I use to measure cathode voltages but it is only good to 6 kilovolts. It is usually not necessary to check the very high PDA voltage; we should be able to get *something* on the CRT without dealing with the PDA.

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2017, 12:59:06 am
content: Quote from: finom1 on May 03, 2017, 12:37:04 amThe link casinada gave is the scan I use for the 7633 and has all of the schematics toward the back. They are even in color; Tektronix liked to use blue ink.http://exodus.poly.edu/~kurt/manuals/manuals/Tektronix/TEK%207633%20%20Service.pdfQuotePDF page 296.QuotePDF page 300.QuoteI usually end up printing out selected schematics on 11x17 paper when working on a problem like this.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 03, 2017, 02:06:44 am
content: I learn something every time I watch an Old64goat video, be it his tech tips or flap.He checked the heat/age failed glue ends 0.15 amp glass fuse with a meter and got 20 ohms reading = not goodI 'may' have missed that with a hurried visual or simple buzz/fast continuity check, especially if I can't pull a fuse out to read values and do a physical inspection.----------------------F W I W:If it was me checking that'please helpI'm sick of auctions and want to work again'Tek 7633, I would first do a basic visual on the unit, the front panel plugin connectors and lube them,then do a turn on, turn up the Intensity, then start working ALL those buttons and knobs at random and in multiples, and see if anything appears briefly on the screen.Working the lot BEFORE applying power first is recommended, especially the power switch and it's banged up dials etc, and then with power applied.Better still, have a mounted video camera or phone running to see on replay what buttons and knob combo caused a brief flicker, trace, spot or no show etcIf no go, try removing and repositioning plugins, in any basic combo possible so the unit will function, till something appears or not.If still no life, roll up the shirt sleeves and give the unit a peaved 'Clint squint'Warm the entire unit up with a portable fan heater and / or use a hairdryer for tight spots, especially if in a cold location and try ALL the above again.No good? Tip the unit on it's side and upside down (carefully) warm/heat up and try again in those positions.FYI to gigglersI fixed a few same vintage 'for parts or not working' 5000 and 4xx series Teks and Phillips exactly this way years ago, and after lubing up any offender dry sticky switches, knobs and connectors, and elbow grease, they worked perfectly and within spec ..without even turning on the multimeter and untangling the leads.If anything, the time spent/wasted? above (one hour at most) will at least confirm that the unit has issues that need thorough service manual based investigative diagnosis, which as you guessed by now, I prefer to AVOID like the plague if I can, loland if you can't fix it or afford repairs, the next swap meet or Ebay will gladly sort it out for you, and get that valuable bench real estate vacant again

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 02:58:32 am
content: David,Bill is having trouble reading his copy of the manual. This is what he just wrote me:"I NEED a service manual I can read, I can't even read the the schematic part numbers and I can't find the HV board in the PDF.I can NOT find schematic 7, I can NOT find schematic 8, I hate this PDF, I have 4 of them and they are all no good, they are so bad I can't even read the parts numbers, voltages, etc..Where is Q1195 on the HV board?Where is C1198 on the Z-AXIS board?What I need is for someone to take a clear photo of these parts OR a Tektronix 7633 service manual from Teltronix in PAPER form..If I can't get a manual that I can't read I will give up."Any ideas?Thank you for helping!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 03:04:26 am
content: Quote from: Electro Detective on May 03, 2017, 02:06:44 amThank you for all that detailed help!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 03:06:51 am
content: Quote from: David Hess on May 03, 2017, 12:59:06 amThank you David for telling him what pages to print!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 05:48:39 pm
content: Hello,Old64goat just sent this message:"As I said I can not find Q1195.I can not find C1198.The way that PDF is set uo I have to scroll through all 320 pages to try to find anything, I hate it."Does anyone know what page Q115 & C118 are located on?Thank you for helping!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 06:03:24 pm
content: I just got another update from Old4goat:"This is getting OLD...LOLI did find Q1185 & C1198 on the HV schematic which I did PRINT OUT, but when I look at the HV board "picture" they are NOT shown.I spent two hours looking at the pictorials & schematics and printed them all out.If Q1195 & C1198 are INSIDE the HV box they must be hidden and are not serviceable.Another thing is how the heck am I going to see if I got +15 volts across C1198 if it is INSIDE the HV box?"Can someone please advice on next steps to take?Thank you for helping!!!

author: tautech
author_rank: Super Contributor
timestamp: May 03, 2017, 06:23:00 pm
content: Quote from: finom1 on May 03, 2017, 06:03:24 pmThis is getting to be hard work with Old4goat. I suspect the transistor he seeks is the main switcher for the HV SMPS, they are normally a TO-220 or similar and bolted to the frame or some heatsink. When this is the case it is often identified in the schematic with a dotted line indicating the device is NOT on the PCB.Service manuals are written for technicians and without knowledge of the conventions used some considerable time studying and comparing with the physical layout MUST be invested for it all to make sense.There are NO shortcuts, he must spend the time to understand the schematics, principles of operation, physical layout and reasons for it all.All we that are self taught have had to follow this path and it need be seen as an investment of time for your future.Good luck.

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2017, 06:48:43 pm
content: Quote from: finom1 on May 03, 2017, 05:48:39 pmAll of the high voltage inverter circuit including C1198 which decouples the unregulated +15 volt supply to the high voltage inverter and Q1195 which is the TO-3 power transistor for the inverter is shown in the upper left corner of schematic 7 which is PDF page 296.The fuse for the unregulated +15 volt supply going to the high voltage inverter is shown on the left side of schematic 8 which is PDF page 300.The 7633 is one of the increasingly few Tektronix oscilloscopes which I have *not* made a compilation of schematics for because the existing freely available service manual scan is pretty good. I have actually done about half of the work to make a set of dedicated schematics for the 7633 so maybe I should complete that. Do not count on anything quickly though as this takes time and the scans would not really look any better than the existing service manual.Q1195 itself is a TO-3 packaged transistor and is exposed where it is mounted to the aluminum cover over the high voltage board. Look under the high voltage test point toward the back of the oscilloscope. (1) The case is the collector so it can be probed with a voltmeter to see if the +15 volt unregulated supply to the inverter is present. Be careful of course not to short it out to the chassis because this will blow fuse F814. When the inverter is operating, the exposed collector of Q1195 is where the primary side oscillating waveform of roughly 40kHz can be measured.Usually the failure in this circuit is Q1195 drawing too much current because of some other failure which blows fuse F814. For this reason if the fuse is blown or if Q1195 is bad, the cover should be removed to gain access to the high voltage circuit board and the parts in the high voltage inverter should be tested. I am not sure how to get the cover off.Sometimes Q1195 is blown and if that is the case, then it can be replaced with a modern On Semiconductor 2N3771G or 2N3772G. The original 2N3055 is a 0.3 MHz part so modern 2N3055s with their 2.0MHz and higher Ft tend to spuriously oscillate but an old 2N3055 could work.For testing purposes, I would remove fuse F814 and use a current limited power supply to power the high voltage inverter through the fuse connection. Alternatively an LM317 configured as a current source with a single 2 watt 1.0 ohm resistor could replace the fuse temporarily.(1) PDF pages 316 and 318 show the location of Q1195 as part number 110 toward the center top of the drawings but I agree with Old4goat, these drawings are difficult to read.

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2017, 07:07:09 pm
content: Quote from: tautech on May 03, 2017, 06:23:00 pmIn this case it is an old slow 0.3MHz 2N3055 operating in a power blocking oscillator. The case (collector) is exposed and visible below the high voltage test point. Earlier oscilloscopes in this series used a push-pull configuration with two 2N3055s and I do not know why Tektronix changed it, maybe the single transistor version was less expensive?

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 07:53:23 pm
content: Quote from: tautech on May 03, 2017, 06:23:00 pmGood advice, thank you for sharing!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 09:14:52 pm
content: Here is an update from the Old64goat:"First here is a quote from David Hess:"All of the high voltage inverter circuit including C1198 which decouples the unregulated +15 volt supply to the high voltage inverter and Q1195 which is the TO-3 power transistor for the inverter is shown in the upper left corner of schematic 7 which is PDF page 296.The fuse for the unregulated +15 volt supply going to the high voltage inverter is shown on the left side of schematic 8 which is PDF page 300."========================================================On ALL my PDF manuals of which I have 4, all the same 320 page PDF files, there are no schematics on pages 296 or 300, so I had to search for them by scrolling through many pages.With that said I found Q1195, THANKS David!I measured the voltage on the collector, it reads +22.3 volts, I know David said +15 volts unregulatedSo could that be normal as it is not regulated?I do have some very old 2N3055 power transistors but I would hate to pull out the HV board and have it blow.BTW I no longer have a transistor tester, years ago I had a Sencore Super Cricket but that got sold dirt cheap.From what David said fuse F814 supply's the unregulated +15 volts to Q1195, but like I mentioned in this posting PDF Page 300 does not show a schematic, in fact there are NO schematic numbers shown in these PDF manuals I have but it does show what circuit they are.This is one big reason I am having such a bad time with these PDF'sTHANKS guys"David, if you have time what do you think?Thank you for helping solve this problem!!!

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2017, 09:38:01 pm
content: Quote from: finom1 on May 03, 2017, 09:14:52 pmThat is the normal voltage. The +15 volt unregulated supply is used to feed the +15 volt regulator and it also feeds the high voltage inverter. Its minimum voltage has to be higher than the dropout voltage of the +15 volt regulator so +22.3 volts is about right.QuoteOur PDF files might have a different number of pages.The schematic numbers are marked in a lower corner with the schematic number.Artek Manuals has a complete scan of the 7633 manual and they includes indexes making it easy to find specific pages for about $7. Their quality is usually pretty good.http://artekmanuals.com/manuals/tektronix-manuals/QuoteIf the inverter is operating, then there should be a high level of AC at the collector of the transistor so look for that using an AC voltmeter or another oscilloscope.I think the only way the inverter could not be oscillating *and* fuse F814 not be blown is if Q1195 was open or if the transformer bias winding to the base of Q1195 was open. If Q1195 and the transformer was good, then the high voltage regulator circuit would drive Q1195 hard blowing fuse F814 and that did not happen.So the likely problem is Q1195 being open. Unfortunately this leaves the question of why which is why I recommend gaining access to the high voltage board to test the transistors in the regulator circuit and measure the resistance of the transformer primary and bias winding.Before taking anything apart, check for an AC voltage on the collector of Q1195. It should be about 40kHz.

author: tautech
author_rank: Super Contributor
timestamp: May 03, 2017, 09:44:40 pm
content: A quick test to see if these inverters are working is to look for the EMI they produce when running. David has mentioned 40 KHz and this can be identified with another scopewithoutconnecting but just using a probe close by, ahla near field probe style.

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 10:33:25 pm
content: Quote from: David Hess on May 03, 2017, 09:38:01 pmDavid, thank you for all the details!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 10:35:16 pm
content: Quote from: tautech on May 03, 2017, 09:44:40 pmtautech, thank you for this information, Bill does have another scope to use to check it.Thank you for helping!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 03, 2017, 11:20:00 pm
content: Here is another update from Bill:"MORE INFORMATION:I removed the fuse F814 and inserted +15 volts, I did this on the end of the fuse holder that goes to the HV supply.My power supply showed about 500ma draw at +15 volts.Then I took my scope and I saw a nice clean sine wave but I could not read the frequency.I then connected my frequency counter using my scope probe set on the RX1 setting because I could not get any reading on the RX 10 setting, it read 41KCNOW hear is the "kicker", I replaced F814 and of course I got the +22.3 volts on the collector, the frequency counter was around 12KC and it fluctuated around that frequency.Very strange it seemed to give me 41KC at +15 volts but not with +22.3 volts.The AC on the collector is low voltage, I had to set my scope to almost the max sensitvity so that is why I set my scope probe to X1."Any ideas on this new information?Thank you for helping out solving this problem!!!

author: Electro Detective
author_rank: Super Contributor
timestamp: May 03, 2017, 11:50:42 pm
content: It appears Old64goat may be in the Tektronix tech trap merry go round I mentioned earlier,working through test points and voltages whilst being hampered by dicky intermittent contact switches, dials, connectors,all working together and at random to prevent triggering and displays on the screen, and come and go not HV readings, and so forth.Assuming of course no half @ssed repairs were performed on this 7633, on a previous owner/s troubleshoot rodeo ride.Too bad I haven't got that 7633 in front of meMr. Carlsons Labtime, would make an awesome tear down and repair video!

author: james_s
author_rank: Super Contributor
timestamp: May 03, 2017, 11:53:26 pm
content: Can anyone confirm whether the HV is directly generated or has a cockroft-walton multiplier? I ask because I've worked on HeNe laser power supplies where the capacitors in the multiplier looked fine at lower voltages but would arc internally at full voltage and short. It might be worth measuring the HT connection while ramping up the HV circuit on a variable bench supply and see if you get any HV up to a certain input voltage.

author: David Hess
author_rank: Super Contributor
timestamp: May 04, 2017, 12:22:44 am
content: So with a higher supply voltage, the frequency was lower and the AC signal was smaller? Here is what I think:1. Aluminum electrolytic capacitor C1198 is worn out. At higher frequencies, the reactance of L1198 will be higher so the AC voltage seen at the collector of Q1195 will be higher. The high voltage inverter will not operate if decoupling capacitor C1198 is worn out.2. Usually the control loop will drive Q1195 hard if the output voltage (-1475) is low blowing fuse F814. In this case, I suspect the fuse was replaced later if it was blown and driver Q1190 transistor was damaged or the gradual degradation of C1198 allowed excess drive current to damage driver Q1190. In that case, Q1187 could supply enough current through the 1k resistor and Q1190's shorted emitter-base junction to raise the current through output transistor Q1195 to the level you measured but not high enough to blow fuse F814 again.3. There is no voltage on the output because of the low impedance of the heater winding, the high impedance of L1198 when C1198 is bad, and low drive current from Q1190.4. Possibly there is a short on the output side like at the high voltage multiplier but that cannot be the only problem. If the problem was only on the secondary side, then fuse F814 would blow.The above is somewhere to start anyway but access to the high voltage board will be necessary to replace C1198 and test driver Q1190. I would just replace C1198 and test the old capacitor. You said that you lack a transistor tester but do you have an LCR meter or impedance bridge for testing capacitors? Just measuring the capacitance should be sufficient.

author: finom1
author_rank: Regular Contributor
timestamp: May 04, 2017, 12:31:05 am
content: Quote from: james_s on May 03, 2017, 11:53:26 pmThank you for helping out!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 04, 2017, 12:32:44 am
content: Quote from: David Hess on May 04, 2017, 12:22:44 amDavid, thank you for this valuable information and sharing your wisdom with us!!!

author: David Hess
author_rank: Super Contributor
timestamp: May 04, 2017, 02:26:09 am
content: Quote from: james_s on May 03, 2017, 11:53:26 pm-1475 volts for the cathode is generated by a half wave rectifier (CR1215) which has a relay which cleverly converts it into a half wave voltage doubler (CR1215 and CR1210) to produce -3000 volts for reduced scan mode.The +7000 volt PDA (post deflection acceleration) is produced by a half wave voltage doubler (one stage of a Cockcroft–Walton multiplier, CR1202 and CR1205) from a higher voltage extended winding on the transformer.It is difficult to control the output because there is closed loop feedback from the -1475 or -3000 volt cathode supply which controls the inverter drive. Just messing with the power to the primary side of the inverter will not control the output well and can damage the oscillator do to excessive current and heat if the input voltage is low.The 7623A is a 7633 without reduced scan mode. The 7623B is effectively a renamed 7633 and replaced both.

author: finom1
author_rank: Regular Contributor
timestamp: May 04, 2017, 11:33:02 am
content: I just fond this information: 7633 Storage Oscilloscopehttp://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7633.htm

author: finom1
author_rank: Regular Contributor
timestamp: May 04, 2017, 08:06:25 pm
content: David,Bill just sent me this message for you:"old64goatI am printing all this information out, David has been a great help to me, please thank him for me!"

author: finom1
author_rank: Regular Contributor
timestamp: May 04, 2017, 09:38:06 pm
content: Here is another update from the Old64goat:"David, I know you had mentioned you did not know how to get out the HV board but do you know if I have to remove the Z-AXIS and the other board on the side of the HV box?You had asked me if I had a capacity bridge, yes I have a SPRAGUE Telo-Mike TO-5.However I do not own a transistor tester so all I can do is use my SIMPSON 260 to test the transistor for shorts.I was getting some sine wave oscillation so could that mean the 2N3055 is good?If so I do not have to remove it, I need to buy some heat sink compound and a mica washer for the 2N3055.IF I can get the HV board "box" out I will replace C1198."Thank you for all your help!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 04, 2017, 10:11:15 pm
content: More pictures from the Old4goat:Does anyone know how to pull out the HV Board?

author: finom1
author_rank: Regular Contributor
timestamp: May 04, 2017, 10:13:27 pm
content: Few more pictures:Looking for any help removing the HV Board!!!Thanks again.

author: David Hess
author_rank: Super Contributor
timestamp: May 04, 2017, 10:40:46 pm
content: Quote from: finom1 on May 04, 2017, 09:38:06 pmI took a quick look at my 7603; it uses the same enclosure over the high voltage board. The enclosure is held on by two side facing screws along the top where the z-axis board is and one down facing screw on the bottom. In order to gain access to the bottom screw, the power supply has to be pulled out from the back.You might be able to leave the z-axis board connected and only have to temporarily unmount it to get to the top two screws.QuoteThat is one cool piece of test gear however I was reading the manual and:2.1.2 CAUTION. The TO-5 should NOT be used to measure the capacitanceof small transistor electrolytic capacitors with low doc voltageratings, or to check the I-R of transistor ceramics rated 50 volts or less.Such capacitors require special test equipment to avoid damage duringtesting.QuoteThat is usually sufficient because most transistor failures are shorts or opens; I always use the diode test function on my DMMs to test the two transistor junctions separately and then do a base shorted to collector test. Do not use the Rx10,000 range on your Simpson 260 for testing transistors; the 7.5 volt potential is enough to cause reverse base-emitter breakdown damaging the transistor.QuoteYes, I think so.QuoteThe mica washer should survive. The high voltage board is mounted to the inside of the enclosure so the TO-3 transistor goes with it. Possibly you will not have to remove the 2N3055 but that can be determined after you have the enclosure pulled back.QuoteReplace C1198 and test the other transistors.Looking at the schematic again, I now think Q1190 may still be good but test the transistors anyway. Possibly the only failure is C1198 and that capacitor is known to wear out in this design.

author: finom1
author_rank: Regular Contributor
timestamp: May 05, 2017, 12:06:30 am
content: Quote from: David Hess on May 04, 2017, 10:40:46 pmDavid,Thank you for all your kindness helping the Old4goat "Bill" out fixing his scope!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 05, 2017, 01:34:22 am
content: Another update video from Bill:Z -AXIS BOARD REMOVAL -Thanks everyone for all your help!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 05, 2017, 01:40:36 am
content: Can someone please instruct the Old4goat on the next steps to take?Thank you!!!

author: David Hess
author_rank: Super Contributor
timestamp: May 05, 2017, 03:01:52 am
content: I forgot about the readout board position on your 7633. You definitely had to remove it.I cannot see it on your video but on my 7603, there are definitely 2 screws behind the z-axis board which hold the cover on so you have to find a way to get that last screw holding the z-axis board to the high voltage cover removed. I used a screwdriver with a thin shaft but larger head. I suppose you could notch that aluminum rail above the screw to gain better access.I think the screws on the side of the high voltage cover are holding the high voltage board to the inside of the cover.The 7603 is a little easier to deal with because the readout board is mounted where the 7633 has its storage board which is forward of the high voltage cover. That was a great drawing that you made for reattaching the cables.Tektronix packed a lot into the 76xx series oscilloscope chassis although the only major addition to the 7633 is the storage board which goes where the 7603 readout board was.

author: finom1
author_rank: Regular Contributor
timestamp: May 05, 2017, 01:30:07 pm
content: Quote from: David Hess on May 05, 2017, 03:01:52 amThank you David for helping!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 05, 2017, 05:39:06 pm
content: This was posted on Old4goat's youtube channel:"Zeebee19718 hours agoHigh voltage compartment dismantling guide: page 4-22 (139 of 320 in pdf document).HIGH-VOLTAGE COMPARTMENTThe components located in the high-voltage compartment can be reached for maintenance or replace-ment by using the following procedure. Diagram 7 shows the location of components in the high-voltage compartment and color-coding of the wires.NOTE All solder joints in the high-voltage compartment should have smooth surfaces. Any protrusions may cause high-voltage arcing at high altitudes.1. Remove the heat radiator/Low-Voltage Regulator assembly as described previously.2. Disconnect the crt base socket.3. Disconnect the crt anode plug and discharge it to the chassis. Using an insulated probe or wire, discharge the jack portion of the crt anode connector to chassis ground.4. Disconnect the multi-pin connectors on the Z-Axis Amplifier board.5. Remove the screw on the bottom of the high-voltage compartment and the two screws located at the top.6. Guide the high-voltage compartment away from the instrument chassis. Be careful not to damage any of the components or the pin connectors on the High-Voltage or Z-Axis Amplifier circuit boards. Dis-connect the multi-pin connectors on the High-Voltage board.7. Using an insulated shorting strap, discharge the exposed connections to chassis ground.8. Disconnect plug P1196 and the four screws which secure the High-Voltage board to the high-voltage compartment. Now, all of the circuitry in the high-voltage box can be reached for maintenance.4-22 REV. B, DEC. 1974Low voltage PSU dismantling guide: page 4-16 (133 of 320 in pdf document).REGULATOR CIRCUIT BOARD REPLACEMENT.1. Remove the four screws which secure the protective cover to the rear of the instrument. Remove the protective cover.2. Disconnect the pin connectors.3. Remove the four screws which secure the Regulator and Fan-Motor subassembly cover to the rear of the instrument.4. Remove the two screws which secure the Fan Motor, and remove theFan Motor.5. Remove the four screws which secure the plate to the heat radiator. Remove the plate.6. Remove the power transistors from the back of the heat radiator. Note the location of each power transistor.7. To replace the Regulator board, reverse the order of removal. NOTE After replacing the power transistors, check that the transistor cases are not shorted to the heat radiator before applying power.4-16 REV. B, DEC. 1974?"Great detailed information, thank you for sharing!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 05, 2017, 05:57:37 pm
content: Update from the Pld64goat:I Am Going IN!!

author: guido
author_rank: Regular Contributor
timestamp: May 05, 2017, 11:44:39 pm
content: It's interesting to get these out, i've done a few. Start at the back: 1. Remove the heat radiator/Low-Voltage Regulator assembly as described previously. Getting one of the mounting screws out is fun, getting it back in again is even more fun..Also interesting is if you start swapping the PCB on top of the HV between mainframes (7603 i think it were). There are two versions, where the 15V connector from the powersupply has + and - swapped (not the arrow on the pcb, but the traces on the pcb). And one scope had a "straight" cable and the other one a "crossed" cable to match the PCBs. So i had to swap the pcbandthe cable from one scope to the other. If you only swap the pcb it won't work. I know from experience.

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2017, 12:08:08 am
content: The more I watch Old64goat's videos and study the 7633, the more I want a 7633 or 7623B. But I already have a 7603, two 7834s, and other 7000 mainframes so it is difficult to justify.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 06, 2017, 08:52:08 am
content: Mr Old64goat is officially in the 'last man standing' tech arena now, about to face unknown adversariesLet's pray he finds a BBQd resistor or two, some dry solder joints, or an easy to replace leaking capacitor, and end this painlessly

author: finom1
author_rank: Regular Contributor
timestamp: May 06, 2017, 06:01:58 pm
content: New update from the Old64goat:It Is Looking More And More Like a Failure -Please help him if you can!!!Thank you for helping!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 06, 2017, 08:19:27 pm
content: Any ideas or suggestions are welcome.Can everyone share this video with people that you know that have Tektronix service experience or anyone with the capability to resolve this issue Bill is having?Thanks everyone for trying to help!!!

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2017, 09:05:11 pm
content: As I recall, a pair of those heavy wires from the rectifier board go to the cooling fan. I ended up adding an inline Molex connector to the wires going to the cooling fan in my 7603 when I removed the fan to lubricate its bearings. My 7603 is one of the weird ones which has an engineering change notice fan which is not documented in any of the service manuals. The fan in my 7603 matches the one in your 7633 probably meaning that both were late production units. That may be related to the status of your high voltage board; see below.I have marked in green what I am sure are L1198 and C1198 in the photograph below. I am actually somewhat relieved that it is an aluminum electrolytic capacitor because I have been trying to verify the exact type without results.However the board in the photo does *not* match the board layout shown in my scan of the 7633 service manual. Besides other minor differences, L1198 and C1198 are swapped in position. The 7633 was produced for a long time so it would not surprise me if some of the boards had major revisions. Tektronix either released updated service manuals or engineering change notices describing modifications made based on serial number. A later service manual will at least show that the board was changed in the parts list.As far as how to proceed, I really think the whole board should be removed whether C1198 can be changed in place or not. All of the aluminum electrolytic capacitors should be changed, the transistors in the high voltage regulator should be tested, and I would also test the high voltage diodes and maybe capacitors although the high voltage parts cannot be tested well without a high voltage low current supply; at least they can be checked for low voltage shorts.I would try to setup the oscilloscope so the board can be operated with only the CRT heater connected or a suitable load resistor used in place of the CRT heater. (1) Then the high voltage output can be verified before reinstalling the board.I know the above would be a lot of work but I think it would be worth it and better than parting the oscilloscope out but of course it is up to you Old64goat. I see that you are in the US but I have no idea of which area; maybe an EEVBlog (or TekScopes@yahoogroups.com or TekScopes2@groups.io) member who can help you out is close.(1) The CRT heater's resistance increases significantly as it warms up (4 times? For incandescent bulbs it is like 10 times.) and I have no idea what value it is at operating temperature so it may be better to use the actual CRT heater for testing.

author: finom1
author_rank: Regular Contributor
timestamp: May 06, 2017, 11:24:33 pm
content: Quote from: David Hess on May 06, 2017, 09:05:11 pmDavid, Bless you for all this detailed information. Great picture, worth a thousand words.Thank you for sharing your wisdom with Bill!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 07, 2017, 01:20:11 am
content: New message from The Old64goat:I have a question for David Hess:===================================================================Here is a quote from David."I would try to setup the oscilloscope so the board can be operated with only the CRT heater connected or a suitable load resistor used in place of the CRT heater. (1) Then the high voltage output can be verified before reinstalling the board"===================================================================Do you mean run this HV board on the bench?I had thought of that but there are so many plugs disconnected from that scope I can't see how I could do it.I would have to ground the case, I would have to feed the +15 volt unregulated voltage to and and who knows where to insert them.Other than the +15 volts do I need any other voltages?If so where do I insert them?I can use some clip leads from the low voltage rectifier board once I find what they are.BIG complex job to say the least.I am not having much luck testing the transistors, too hard to see the pins and of course I am testing them in circuit with my DMM on "diode" test.David, once again THANKS for all your help

author: finom1
author_rank: Regular Contributor
timestamp: May 07, 2017, 01:21:49 am
content: Another update from The Old4goat:OKAY here is what I found now that I can see the board clearly:C1198 which should be 47uf reads 44.1uf on my Chinese digital capacity handheld meter.There is no leakage spilling out of that cap, in fact everything on that board is very clean except around the red HV lead and the components near it, there is a very light grey deposit like you find near any HV anode lead.Under the board there is a yellow .1uf @600 volts, I tested it in circuit like I did with C1198 and it reads very close to .1uf.Thank you for all your help.

author: David Hess
author_rank: Super Contributor
timestamp: May 07, 2017, 01:12:12 pm
content: Quote from: finom1 on May 07, 2017, 01:20:11 amThat is exactly what I mean but the power supply is going to need to be connected to the high voltage board. The high voltage inverter requires +15 volts unregulated, +5 volts, +15 volts, +50 volts, and +130 volts.It might be possible to get away without doing this if the high voltage board is extensively tested and refurbished. The problem is knowing that it is working correctly before reinstalling it.If I was desperate to avoid a working test of the high voltage inverter while it is removed, then I would change C1198, unambiguously test the transistors in the regulator, test for shorted high voltage capacitors and diodes, test for a short between the high voltage transformer secondaries, and disconnect the input to the high voltage multiplier. Then I would reinstall the high voltage board and see what happens. The CRT will not work properly without the PDA but if the -1475 cathode voltage comes up, then something will be visible.At that point if the CRT works, then the high voltage multiplier may or may not be shorted and it would need to be reconnected to test it.QuoteThe standard DMM diode test may not work in some cases for accurate in-circuit measurements.Quote from: finom1 on May 07, 2017, 01:21:49 amIt is possible although unlikely that the capacitor has excessive ESR without having lost a lot of capacitance. If it was unambiguously bad, then that could save a lot of time and effort but now we have to consider if there is a more serious problem elsewhere.The common problems I have read about (1) with Tektronix high voltage inverters include:1. Leaking or shorted high voltage capacitors or diodes.2. Leaking or shorted high voltage multiplier. This is just a special case of #1.3. Worn out C1198.4. Bad transistor in the high voltage regulator.5. Leaking or shorted high voltage secondary on inverter transformer.I am suspicious in your case that fuse F814 was not blown. To me that points to a problem with the high voltage regulator because if there was no output, it should drive the inverter very hard blowing the fuse. On the other hand, absolutely no output at the -1475 test point indicates a short in the high voltage circuits.(1) I have lots of Tektronix oscilloscopes and none have suffered a high voltage inverter failure and the ones I have bought just to have fun fixing did not have high voltage problems.

author: finom1
author_rank: Regular Contributor
timestamp: May 07, 2017, 06:30:23 pm
content: Update from Old4goat, here we go:I Did Not Give up Yet -You can do it!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 07, 2017, 06:34:25 pm
content: Dave Hess,What does Bill have to do next?This will be such a great success story!!!With your help he will succeed.Thank you for sharing!!!

author: David Hess
author_rank: Super Contributor
timestamp: May 08, 2017, 01:34:31 am
content: I had some fun brushing up on my Photoshop skills. Here is a slightly cleaned up scan of the high voltage board schematic showing what parts I would initially check in circuit for shorts and opens at low voltage. The board layout I have does not quite match the newer board you have so hopefully you can find everything.Pay real close attention to C1228 toward the right side of the schematic and check it first. R1226A and R1226B are the feedback divider which sets the -1475 output voltage. If C1228 was shorted, then the regulator would hold the output voltage at about 1 volt and the inverter at a very low power level without blowing the fuse which is what you observed.

author: finom1
author_rank: Regular Contributor
timestamp: May 08, 2017, 07:09:34 pm
content: New update from the Old4goat:I Am At A BRICK Wall -Thank yo for any help you can give him!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 08, 2017, 07:36:54 pm
content: Is this the Q1195 pinout Bill was talking about not being able to read the numbers?

author: David Hess
author_rank: Super Contributor
timestamp: May 08, 2017, 08:10:50 pm
content: 1. The neon bulbs are used as low leakage low capacitance voltage suppressors between the cathode and other tube elements. This is the first time I have not seen them included on the schematic. They will often briefly flash when the instrument is turned on or off.2. The multiplier could be bad but I do not think we would see the symptoms of zero cathode voltage and an intact fuse if that was the case. Like I posted earlier, I would disconnect the input to the multiplier until the rest of the board works.3. The flat black discoloration on the left side of the high voltage multiplier is soot attracted by the high positive electrostatic potential and is completely normal. All CRTs with PDA (post deflection acceleration) accumulate that to some extent.4. I was very surprised to see that the layout for the high voltage multiplier is included in figure 8-11. Tektronix refers to it as A9 - Anode Board. If the multiplier was bad, then I would build a new one from scratch.5. The pin numbers shown on the schematic at the 2N3055 from top to bottom are 2, 3, 1 for the molded transformer and 5, 1, 2 for the dipped transformer. So there must have been two different inverter transformers used.6. My guess is that two of the pins on the primary side are for the +600 volt DC secondary winding and I am sure that the two brown leads coming out of the top are for the CRT heater winding.7. The +50 volt marking is for diode CR1216. The winding shown below it is for the +600 volt DC output and also drives the focus and z-axis restorers with AC.8. That big red capacitor looking thing under the high voltage multiplier is the reed relay. The glass envelope can be seen at the ends. My guess is that it is a high voltage vacuum reed relay but I do not remember ever seeing one before.9. The CRT circuit schematic includes a partial A8 z-axis amplifier and the A9 anode board. Their are outlines on the schematic separating the different boards. Usually at the bottom of each outline, it is marked for which board it applies to. The original drawing has the board outlines highlighted in blue.10. There is a TO-92 packaged black plastic transistor with a metallic blue flat between the two metal can transistors you counted. I think Motorola liked to mark their TO-92 transistors that way.11. Those vertically mounted boards on the high voltage board must be the focus DC restorer and the z-axis DC restorer.12. The relay coil is marked K1177 and it is shown below and to the right of the inverter transformer on the schematic. It is left of the RS HORIZ GAIN adjustment.13. The high voltage multiplier with part number 152-0682-00 has a date code of 8726 so this oscilloscope was produced sometime after the middle of 1987 making it one of the last ones. The 7633 was produced from 1974 to 1990. The 7623B which replaced it was only made in 1991.14. The plugs all have pin 1 marked with an arrow on the plastic body and usually a marking on the board.

author: David Hess
author_rank: Super Contributor
timestamp: May 08, 2017, 08:12:45 pm
content: Quote from: finom1 on May 08, 2017, 07:36:54 pmYes. That is actually the pinout for the connector on the board. Based on the notation, there were two versions of the inverter transformer and they used a different pinout for the connector going to the transistor.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 08, 2017, 08:28:09 pm
content: Do the transistors have little white marks on the bottom of the pins? Those are sockets, the transistors pull out.

author: David Hess
author_rank: Super Contributor
timestamp: May 08, 2017, 09:30:28 pm
content: Quote from: Cyberdragon on May 08, 2017, 08:28:09 pmI do not know exactly when they changed but late production from Holland did not use the Berg Miniserts found on earlier production. I have some plug-ins like this and the small signal transistors are soldered into place.When I am working on these, I remove the transistors and install individual collet pins so the transistor can be replaced without soldering.

author: finom1
author_rank: Regular Contributor
timestamp: May 09, 2017, 01:13:30 am
content: Thanks everyone for all your help!!!

author: Martin.M
author_rank: Frequent Contributor
timestamp: May 09, 2017, 06:37:18 pm
content: if the low voltage PSU is failed, I am pretty shure to have one in the spare parts cabinetMartin

author: Electro Detective
author_rank: Super Contributor
timestamp: May 10, 2017, 11:37:41 pm
content: Old64goat needs to kick back and take a breakand listen to some nice music to get pumpedbefore going back into the arena

author: finom1
author_rank: Regular Contributor
timestamp: May 11, 2017, 02:23:15 am
content: Update from The Old4goatThanks everyone for helping!!!

author: BravoV
author_rank: Super Contributor
timestamp: May 11, 2017, 04:12:30 am
content: Not contributing much, but at last video he mentioned there are so many plugs that were unplugged, and need to be plugged correctly. And with that many plugs dangling like that, have to admit they're error prone especially when get distracted.My tips, use camera, heck, even a crappy cell phone camera will do, as long he can get clear enough picture at close distance as documentation,beforeunplugging them. I did that every time when tearing down stuffs, or desoldering bunch of interconnect cables.

author: finom1
author_rank: Regular Contributor
timestamp: May 11, 2017, 06:06:02 pm
content: From youtube:Zeebee19712 hours ago (edited)Diodes CR1202, CR1203 type VG-12Xhttp://pdf.datasheet.live/d016da9f/microsemi.com/VG-12X.pdf"Improved" Tektronix voltage doubler schematic:https://ibb.co/hhSCY5You can use other transformer secondary lead to connect ac test voltage to the doubler but it is risky without current limiter (very thin secondary coil wire). You can also use signal generator and connect it to the primary side, but you don't have a HV probe (you can control filament voltage only).?

author: David Hess
author_rank: Super Contributor
timestamp: May 11, 2017, 08:33:22 pm
content: Quote from: finom1 on May 11, 2017, 06:06:02 pmThe high voltage diode selection is not all that critical. They need to be high voltage, voltage derated, and fast recovery.QuoteI like this idea but it may be perfect for Old4goat in a different form.Disconnect Q1195 and drive the collector winding with a standard function generator. Now the input voltage can be carefully controlled and monitored and the output voltages can be measured. No load will be needed on the CRT winding and no other connections to the board will be needed or are even desired; disconnect everything.If there is a low voltage problem on the secondary side which seems likely, then it will be possible to track down without using a high voltage probe.Termination of the function generator's output is not required because of the low frequencies of up to about 40kHz however function generators usually have a 50 ohm series termination limiting them to about 300 milliamps into a short. This should be enough but if it is not, then a small single ended push-pull amplifier will help drive the inverter transformer to higher outputs.

author: finom1
author_rank: Regular Contributor
timestamp: May 12, 2017, 01:50:02 am
content: New update from The Old64goat:Any help would be greatly appreciated!!!

author: oldway
author_rank: Super Contributor
timestamp: May 12, 2017, 06:48:49 am
content: I have not intervened until now because I have repaired many analogue oscilloscopes of different brands, including Tektronix, but never a 7633.For me, there are only two possible faults: faulty transformer or faulty voltage doubler.You worry about things you do not have to worry about: desolder the wire of the voltage doubler that goes to the transformer, whatever the insulation there is on it. You don't have to worry about this insulation !Power on the scope with the HV board without the voltage doubler and check if you have the - 1475V on the cathode of the tube.There is no problem to let this auto-oscillator working without load because it is not a flyback and it has a regulation circuit of the -1475V voltage.If you have the correct -1475V voltage, it is the voltage doubler that is defective, if not, it is the transformer that is dead.Since there are many connectors on this HV board and that there is a risk of error in reassembling the scope, David Hess's proposal is also a good option.Again, desolder the wire of the voltage doubler that goes to the transformer.It seems to me that 40Khz is a bit high, I believe that these auto - oscillators work rather at a frequency close to 25 Khz.Connect the probe (x10 or x100) of your oscilloscope between the ground and the terminal where you have desoldered the voltage doubler wire and feed the transformer primary as you do with 25Khz, but starting from 0V ... (filament of CRT NOT connected !)Slowly increase the output voltage of your function generator and check the voltage at the secondary with your oscilloscope.If you have a very low voltage or nothing, the transformer is faulty.Nb: some scopes as Philips PM3264 have well known issues of corona discharges, but their HV voltage is 17KV's, not 7KV's as this Tektronix 7633.

author: David Hess
author_rank: Super Contributor
timestamp: May 12, 2017, 01:09:54 pm
content: Quote from: oldway on May 12, 2017, 06:48:49 amThese two faults would normally be my first suspicion as well except for the following:1. There is little or no history of transformer faults in the 76xx series storage oscilloscopes. (1)2. There is little or no history of high voltage multiplier faults in the 76xx series storage oscilloscopes. (1)3. If there was a transformer short or a high current short on the secondary side, then the high voltage regulator circuit should drive Q1195 hard enough to blow fuse F814.4. Nothing was measured on the secondary. Even with a short, I would have expected something on the secondary side if the primary side was oscillating at all which it apparently was but at a very low level.Now maybe there are two faults with a shorted transformer or output and damage to the high voltage regulator circuit. One could have caused the other.One odd thing I noticed about the 7633 high voltage inverter is that unlike the 465 series high voltage inverter which is practically identical, the 7633 implementation has no primary side over-voltage protection. I wonder if they did not think it was needed or left it out to save space. I mention this because if it ran away, then the transformer or secondary side would likely have been damaged.QuoteI could measure the frequency of the high voltage inverter on my 7603 but it uses a different configuration with balanced drive using two 2N3055s. The 465 series which uses practically the same inverter configuration as the 7623A and 7633 operates at roughly 50kHz.(1) Maybe there is no such history because the high voltage inverter and multiplier are so difficult to access and diagnose that people give up on it.

author: oldway
author_rank: Super Contributor
timestamp: May 12, 2017, 02:14:30 pm
content: When you say there is little or no history of faults in the HV transformers or in the voltage doublers of this oscilloscope, you make use of the rules of statistics.But the statistical rules tell us also that there is more risk of faults in a circuit with high voltage or with high current than in another circuit.NB: I don't know if Q1195 (TO 2N3055) has been checked for low Hfe ?A Q1195 with very low Hfe could explain why it is oscilating at very low level without burning the fuse.

author: finom1
author_rank: Regular Contributor
timestamp: May 12, 2017, 03:40:56 pm
content: Quote from: oldway on May 12, 2017, 06:48:49 amThank you Oldway, good to hear from you:)

author: finom1
author_rank: Regular Contributor
timestamp: May 12, 2017, 03:43:58 pm
content: Thanks everyone for trying help The Old4goat out!!!

author: finom1
author_rank: Regular Contributor
timestamp: May 12, 2017, 03:58:37 pm
content: New update from The Old64goat:Here is what I found out:I removed the HV multiplier from the HV transformer and I fed in 100 volts AC 60cly from my varac, I got 60 volts out of the multiplier.Next I put in 40 KC then lowered it to 25 KC, I had my scope probe on the secondary of the HV transformer where the HV multiplier was connected, NOTHING no signal, I turned up my function generator to max and even set my scope probe to RZ-1, again nothing.I put my scope probe on pin 3 of the 2N3055 plug and got my signal.Then I took the resistance readings of the HV transformer, here is what I got:From the HV transformer terminal where the two HV diodes connect to the reed relay to where the HV multiplier was connected I got 100 ohms.Next I took a reading from where the HV multiplier was connected on the HV transformer to the terminal where R1217 (10K) is connected and got 163 ohms.Finally I took a reading from where R1217 (10K) to the HV diodes and got 62 ohms.I think I got a bad HV multiplier AND a bad HV transformer, replacing the HV board may be the only way but I am not going to dump big money that I do not have into this.THANKS to all who have helped me on this!!!

author: oldway
author_rank: Super Contributor
timestamp: May 12, 2017, 04:52:12 pm
content: The voltage multiplier seems to be OK, low output voltage is normal because frequency of 60Hz is far too low for normal working.But HV transformer seems questionable.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 12, 2017, 10:16:43 pm
content: If it's Game Over, time to put it all back together,double check all connections,turn the sucker on,get verified signals going into it,play with ALL the controls, tweaking the trigger dial and switches whilst doing so,then if no life, officially declare it DUT DOAIf you don't need a cool looker retro doorstop or bookend, then it's Ebay time,or flog it off here at EEVblog

author: finom1
author_rank: Regular Contributor
timestamp: May 12, 2017, 11:09:03 pm
content: New update from The Old64goat:"Anyway here are the measurements of the HV board without the metal case that has the 2N3055 on it:6" long, 2" wide and 2" thick.NOW I found an open transistor on the Z-AXIS board using my SENCORE Cricket but it is too hard for me to see let alone replacing it.So if one of those guys would be willing to replace that bad transistor on the Z-AXIS booard as well as checking out the HV board I will give the dementions of the Z=AXIS board:6" long, 2" wide and 3/4" thick.I only tested two transistors on the Z-AXIS board so there may be more bad transistors.As I understand that board is part of the CRT circuit.Bill"

author: David Hess
author_rank: Super Contributor
timestamp: May 12, 2017, 11:20:10 pm
content: I am not convinced the high voltage transformer is bad but I can understand not wanting to mess with it anymore. There are other tests I would do for confirmation and it is not clear to me exactly how Old64goat tested it.To me this seems like an ideal 7633 to repair for someone who is familiar with them. Whatever is going wrong with the high voltage board is probably the only problem.

author: David Hess
author_rank: Super Contributor
timestamp: May 13, 2017, 04:18:21 am
content: I did a little research on replacement parts.There *is* a history of 7633 transformer failures although probably no more than any other 7600 series oscilloscope. My guess is that most diagnosis never get that far because of difficult access to the high voltage board. The 7623A used the same transformers.Replacement transformers are non-existent. Replacement high voltage boards are expensive. However you can probably get a 7623A (1) or 7633 with a known working high voltage board which has the transformer for $40 or less on Ebay; unfortunately shipping will be like $60. Maybe a cheap 7623A or 7633 can be found on Craigslist to save on shipping charges.Q1184 151-0126-00 2N2484 NPN High Gain AmplifierIdeal replacements: 2N5088/9 BC546/48/50Would probably work: 2N3904Q1187 151-0188-00 2N3906 PNP General Purpose AmplifierIdeal Replacements: 2N3906Would probably work: 2N4403 2N2907Q1190 151-0136-00 2N3053 Medium Power AmplifierIdeal Replacements: MJE180/1/2Would probably work: 2N4401 2N2222 (2)Q1195 151-0140-00 2N3055 Power Transistor 0.3MHzIdeal Replacements: 2N3055 (0.3MHz) 2N3771G 2N3772GWould probably work: 2N3055AG MJ15015(1) I found suitable 7632As which went for $10 and $25 recently on Ebay and they also included some plug-ins. The shipping cost for each was about $60 though.(2) For extra derating, I might use a pair of Vbe matched 2N4401s in parallel if I did not have a suitable TO-126 or TO-225 packaged transistor. There are higher power TO-92 transistors but they are more expensive than the recommended MJE180 series.

author: oldway
author_rank: Super Contributor
timestamp: May 13, 2017, 06:52:26 am
content: I am also not sure that the transformer is defective, it would be necessary to make additional tests.The current with a 600R function generator is very low, perhaps insufficient.50R was already much better.Ideally, the primary of the transformer should be supplied from a LF amp with a 4.7R series resistor.Magnetizing current and transformer ratio would be compared with values of a known good working transformer of the same type....but this is not available....Repairing without spare parts is something very difficult....

author: finom1
author_rank: Regular Contributor
timestamp: May 13, 2017, 07:40:18 pm
content: New update from The Old4goat:Thank you for all your help!!!

author: oldway
author_rank: Super Contributor
timestamp: May 14, 2017, 04:52:07 am
content: A faulty transformer can't have any resonance because it is damped by the internal short circuit between turns or layers...This transformer is resonating at 25Khz (the frequency I was thinking it works), then I am now 100% sure that this transformer is OK....That's a very good news.The next step should be to reinstall the HV board in the scope without connecting the voltage multiplier and check if we have the -1475V.

author: finom1
author_rank: Regular Contributor
timestamp: May 14, 2017, 10:48:35 pm
content: Final message from The Old64goat:Bill sends a heart felt"Thank You"to everyone that has helped him. Everyone has shown there are still goodhearted people left in the world that will help someone in need!!!Bless you gentlemen for helping Old64goat!!!

author: Harb
author_rank: Regular Contributor
timestamp: May 15, 2017, 06:47:37 am
content: LOL.....I can picture him jumping up an down on that HT board..........

author: oldway
author_rank: Super Contributor
timestamp: May 15, 2017, 07:44:03 am
content: Sorry that my post caused such a reaction .... but there was perhaps a mistake from the beginning ....Old64goat should have been advised not to attempt this reparation.The Tektronix oscilloscopes were very sophisticated and considered the best analog oscilloscopes on the market.This is paid when trying to repair them ....I think that even if he was not handicapped, he would really have great difficulties to repair this oscilloscope ... then I understand that he wants to make his blindness responsible for his difficulties, but it is not .Even with a lot of experience, a technician fails to repair 100% of the faulty devices ... it's not a failure, we must just accept this reality.At least, he has certainly learned a lot of thinks with this repair, this is what is the most important

author: finom1
author_rank: Regular Contributor
timestamp: May 16, 2017, 01:10:40 am
content: This topic will no longer be active. It has come to a final conclusion!!!Thanks everyone for your valuable input!!!

author: kcbrown
author_rank: Frequent Contributor
timestamp: May 16, 2017, 01:18:27 am
content: I wouldn't remove the topic. The advice given here is just as sound for someone else who might encounter a similar issue down the line. It's great stuff, and it would be a shame for it to disappear just because this particular repair attempt didn't have a good outcome.

author: finom1
author_rank: Regular Contributor
timestamp: May 16, 2017, 01:30:05 am
content: OK, I will take your advice and leave it up.The Old64goat wants everyone to know he " sure does appreciate everyone helping him out". He wishes "all the best" for everyone here!!!

author: David Hess
author_rank: Super Contributor
timestamp: May 16, 2017, 05:42:45 pm
content: Quote from: oldway on May 15, 2017, 07:44:03 amThe first paragraph of my first post had such a warning but maybe I was not emphatic enough.QuoteThere were a lot of suggested simplified non-destructive tests which he did not follow through on that might have revealed the problem. The communications channel was pretty indirect so maybe he never saw them.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 18, 2017, 07:15:08 am
content: Old64goat gave it a good shot, better than most btw,time to handball it to the next player, and move onBeen there, can't win them all

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 19, 2017, 01:22:51 am
content: Another dead piece of gear was Widlarized...can we get a "smash" emote?

author: Electro Detective
author_rank: Super Contributor
timestamp: May 19, 2017, 08:46:40 am
content: Quote from: Cyberdragon on May 19, 2017, 01:22:51 amIs he a mate of Mr. PhotonicInduction?

author: harrimansat
author_rank: Regular Contributor
timestamp: May 19, 2017, 08:59:57 pm
content: Mine had the same problem, and it was bad HV transformer.Replaced and working againReagards!

author: David Hess
author_rank: Super Contributor
timestamp: May 20, 2017, 05:54:04 pm
content: Over on the TekScopes@yahoogroups.com email list we have a member who rewinds the transformers using the original cores although I do not remember if he has done a 7623A/7633 transformer. A couple of other members have done this as well.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 20, 2017, 07:12:17 pm
content: Quote from: David Hess on May 20, 2017, 05:54:04 pmDo they reassemble Widlarized circuit boards too?

author: harrimansat
author_rank: Regular Contributor
timestamp: November 27, 2022, 11:04:21 pm
content: Bad HV transformer