Oscilloscope Tektronix 2465 don't turn on - Page 1
Forum section: electronics / repair

author: Giovanni28
author_rank: Contributor
timestamp: September 07, 2015, 03:24:57 pm
content: I have a Tektronix oscilloscope 2465, but unfortunately the CRT High Voltage Power Supply Circuit Board does not work anymore ("black smoke"). I bought a replacement board on ebayhttp://www.ebay.it/itm/201258583548?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITReading the service manual, under "Adjustments CRT," I saw that you need to have a Time-Mark Generator to generate a 10us time markers. Unfortunately I do not have this tool, but I have a function generator Rigol DG1022, is it fine as a substitute?Any suggestions for the adjustment of the trimmers is pleasing.

author: wn1fju
author_rank: Frequent Contributor
timestamp: September 07, 2015, 05:47:29 pm
content: Should be good enough. Just set the function generator to produce narrow pulses at the desired rate (or interval) and align them all with the graticules on the screen as you make the adjustment. Typically a true time mark generator will probably produce faster rise times than you will get with the function generator, but as long as you make the graticules align with the same voltage on all the slower rise time pulses (say, on the left rising edge), you should be OK.

author: tautech
author_rank: Super Contributor
timestamp: September 07, 2015, 08:03:21 pm
content: Quote from: Giovanni28 on September 07, 2015, 03:24:57 pmNormally a Time-Mark Generator is for the Cal procedures, does thie CRT HV board have Cal trimmers?If so, wn1fju's advice should suffice.

author: Giovanni28
author_rank: Contributor
timestamp: September 07, 2015, 08:16:11 pm
content: Thank you! The new board must still be sended, when it will arrive most likely I will still need your help.This is the new board. The seller says it is compatible with my oscilloscope.this is the old board

author: wn1fju
author_rank: Frequent Contributor
timestamp: September 07, 2015, 10:47:33 pm
content: Yes, I was just assuming Tektronix called for a time mark generator as part of the horizontal cal procedures, not anything specific to the CRT adjustments. I took a quick look at the service manual and that seems to be the case.BUT, let me take this opportunity to rant a little about Tektronix cal procedures. They usually call for specific pieces of equipment (usually their own brand, but not always), then tell you how to set the knobs on them and on the unit under test. So if you don't have the specific piece, you have to figure out what they are trying to do and then look around your lab for something equivalent. Not too bad usually. But, then Tektronix marches you through step by step without really telling you what's going on or why. I guess this is so an "untrained" person could theoretically do the cal. However, God forbid you miss or skip a step, because usually the support equipment and unit under test have been set a certain way 10 pages ago and then modified 50 times since. I've calibrated several dozen vintage Tektronix pieces over the years and it is always a chore.Having said all this, after looking at the service manual, I would be astonished if you had all the necessary equipment. Even if you did, I would be astonished if you could get through the cal procedure without making a mistake.Rant completed.

author: MarkL
author_rank: Unknown
timestamp: September 08, 2015, 12:23:47 am
content: Assuming the scope was calibrated beforehand, you don't need to go through the whole calibration procedure if all you're doing is replacing the CRT electronics. You don't need all the cal equipment.Here's what you can do instead:First, you'll need to perform the "CRT Adjustments" section to accommodate HV, grid, and other CRT-related voltage changes. Use the calibrator output as a simple signal source. Don't mess with the Z-axis transient adjustment unless necessary.Adjust "Dynamic Centering".Then, turn on the deltaV cursors and set them to a value that covers a full 8 divisions (ex: 8.0V if on 1V/div). Use the vertical gain (R638) and vertical centering (R639) to make the cursors overlay the very top and very bottom graticule line. Check that the full motion of either of the cursors is centered around the center on the screen. It may take a few iterations to get a best result. (On my 2465, the cursors don't go any further than the top and bottom graticule lines anyway, so they're always centered in motion, but I don't know if this is generally true.)Similarly, turn on the deltaT cursors and set them to a value that covers a full 10 divisions horizontally, adjusting horizontal x1 gain (R860) and horizontal center (R801) to make the cursors overlay the very left and very right graticule lines. Check centering as above. Turn on horizontal x10 and adjust horizontal x10 gain (R850). Again a number of iterations may be needed to find optimal settings.The reason the above works is you're just re-adjusting the screen to make the cursors show the right signal values. The best approach is still a full re-cal, but I've found this can suffice as long as the scope was correctly calibrated.

author: Giovanni28
author_rank: Contributor
timestamp: September 08, 2015, 02:47:25 pm
content: Quote from: MarkL on September 08, 2015, 12:23:47 amSo the service manual under "CRT ADJUSTMENTS", are you telling me I have to do the first 4 steps?1. Adjust ASTIG Preset (R977) and Grid Bias (R1878)2. Adjust TRACE ROTATION (R975) and Y-Axis Alignment (R1848)3. Adjust Geometry (R1870)4. Adjust Edge Focus (R1864)and steps 5 (Adjust Z-Axis Transient Response (R1834)) and 6 (Adjust High Drive Focus (R1842)) NO

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: September 08, 2015, 03:16:55 pm
content: Quote from: MarkL on September 08, 2015, 12:23:47 amHaving recently replaced the CRT on my 2467B, I found this to be exactly the case. I did an earlier CAL 01 on the scope, and everything was good to go at that point, so I figured the electronics were set. Changing the CRT would just mean accounting for the differences in Horiz/Vert deflections/gains of individual tubes. I set everything you mentioned, and it seems quite happy. So I think I can confirm this abbreviated CRT CAL procedure works.

author: MarkL
author_rank: Unknown
timestamp: September 08, 2015, 08:36:31 pm
content: Quote from: Giovanni28 on September 08, 2015, 02:47:25 pmActually, I'd recommend working through the entire CRT Adjustment section. (I previously said just NOT the Z-Axis transient response, but that's also on your new HV board, so you should do that too.) Again, you can just use the calibrator input to give you a signal to examine. I've also found it useful to turn on the BW limiter when working on focus related adjustments to give you a nice crisp trace.In general, it's unlikely that the settings on your new HV board will be optimal for your specific CRT. You'll probably need to tweak all the pots. And like most analog adjustment routines, it's going to be an iterative process until you reach the best compromise for overall display quality.Mark the pot positions with a marker before you move them in case you get totally off and want to start again.

author: Giovanni28
author_rank: Contributor
timestamp: September 21, 2015, 09:26:44 pm
content: Unfortunately, the card A9 was not responsible!I disassembled the board A2 and I realized that there were two capacitors "broke", the C1016 and C1018; Resistor R1016 was also burned. I have replaced all three components and I reassembled the whole. Unfortunately still does not turn. No signs of life. Any suggestions on some equipment to be controlled and / or measures to be carried out is welcome.

author: Bryan
author_rank: Frequent Contributor
timestamp: September 22, 2015, 12:53:29 am
content: Probably the best thing you can do is get a hold of a service manual, readily available online. Start with the voltage checks on the power supply and go from there. There was a recent post a couple days ago and a user posted a picture of the dip socket on the mainboard and the page from the manual to verify the power supply voltages.https://www.eevblog.com/forum/repair/another-2465-300mhz-to-repair/

author: MarkL
author_rank: Unknown
timestamp: September 22, 2015, 01:54:15 pm
content: Check that the main fuse on the back (F90) is ok.And, yes, definitely check the power supply output voltages.If they're all zero, given that the dead components C1016, C1018, and R1016 are all on the primary side of the power supply, you could start by making sure there's DC coming out of CR1011 (approx 264VDC, according to the schematic).USE CAUTION! This and other voltages on the A2 board are at line potential and are dangerous. Also, if some of the power supply is functioning, capacitors may remain at dangerous voltages after the unit is unplugged.

author: Giovanni28
author_rank: Contributor
timestamp: September 22, 2015, 10:18:46 pm
content: Quote from: MarkL on September 22, 2015, 01:54:15 pmThe main fuse (F90) is ok.QuoteThe DC coming out of CR1011 is OK.I checked the A3 board and I finded the capacitor C1023 was shorted.I hope that now everything is ok!

author: Bryan
author_rank: Frequent Contributor
timestamp: September 23, 2015, 01:19:52 am
content: Best to change out all the electro caps on the power supply board. Just a note if replacing by the schematic there is a error with one of the caps shown in the schematic as it's shown installed reverse polarity. So just note when pulling them out the correct polarity. You will know they are leaking as soon as you unsolder as they will give off a fishy smell.

author: Giovanni28
author_rank: Contributor
timestamp: September 24, 2015, 12:53:14 pm
content: I can not find the capacitors to replace the silver in the picture (250uF 20V C1114 and C1115 - 180uF 40V. C1113 and C1116 - 10uF 160V. C1132); have you any suggestions for me?

author: SeanB
author_rank: Super Contributor
timestamp: September 24, 2015, 03:33:35 pm
content: C1114, C1115 replace with 220uF 50v capacitors, they will fit. C1113/6 replace with 10uF 200V.Buy 105C versions, preferably Panasonic, Nichicon or Rubycon, not mystery branded ones. Those are almost older than me.......

author: Giovanni28
author_rank: Contributor
timestamp: September 24, 2015, 05:06:47 pm
content: Quote from: SeanB on September 24, 2015, 03:33:35 pmWhy values are so different from 180uF to C1113/6? I apologize, but also capacitors C1110 and C1111 are 250uF 20V.

author: dan3460
author_rank: Frequent Contributor
timestamp: September 24, 2015, 05:34:17 pm
content: I read somewhere that one of those caps, I think is the green one besides the transformer, must be exactly 100uF to give you exactly 15V (I think, quoting from memory).This comes from the Tektronix group in yahoo, which I have tried to join in several occasions but no luck.

author: SeanB
author_rank: Super Contributor
timestamp: September 24, 2015, 05:39:43 pm
content: 180uF and 250 uF can be replaced with 220uF, and using a 50V rated unit makes it easier to just use the same higher voltage all round, they will still work on the 20V rail.Sorry, replace 10uF with 10uF, and the most common voltage over 160V is 200V.You can almost always go higher in rated voltage provided it physically fits, and with capacitance values on electrolytics they in any case will have large tolerances on the old ones, typically +100 -50%, so a modern one with +-20% tolerance can replace the 2 different values easily. Just measure the old ones diameter and hight so you can ensure the replacement parts will fit in the space. Most modern capacitors will do so, as they are likely physically smaller in diameter and hight for the same value, just from improved foil manufacturing enabling the use of a thinner foil.

author: Bryan
author_rank: Frequent Contributor
timestamp: September 25, 2015, 12:56:56 am
content: Spreadsheet of the values and the corresponding order numbers. Original has been changed by me to include some changes in part numbers.

author: Giovanni28
author_rank: Contributor
timestamp: September 29, 2015, 07:26:43 pm
content: I replaced all the electrolytic capacitors and also those of polypropylene. therefore, I assembled all the oscilloscope and finally went back to work.I would also replace the electrolytic capacitors from board A1, but scares me the idea to remove the front panel and connections to the CRT.

author: dan3460
author_rank: Frequent Contributor
timestamp: September 29, 2015, 08:23:33 pm
content: The front panel is easy to remove. There are instructions on the removal of all boards in the service manual.

author: tautech
author_rank: Super Contributor
timestamp: September 29, 2015, 08:27:09 pm
content: Quote from: Giovanni28 on September 29, 2015, 07:26:43 pmIt will not be a problem if you have a good selection of tools, 1/4 drive socket set, hex keys etc

author: Giovanni28
author_rank: Contributor
timestamp: September 30, 2015, 09:10:52 pm
content: Unfortunately, I removed the motherboard A1 to replace the electrolytic capacitors, but now the result is what you can see in the photos below.It definitely something wrong has reassemble. Can you help me please.

author: MarkL
author_rank: Unknown
timestamp: September 30, 2015, 09:45:39 pm
content: All the front panel lights are on. It's not getting through the boot process.I would go back and start again with checking the DC power supply outputs, as Bryan had described in post #10 in this thread.https://www.eevblog.com/forum/repair/another-2465-300mhz-to-repair/

author: Giovanni28
author_rank: Contributor
timestamp: September 30, 2015, 10:09:06 pm
content: Quote from: MarkL on September 30, 2015, 09:45:39 pmSorry, but in the post there is no Bryan.

author: MarkL
author_rank: Unknown
timestamp: September 30, 2015, 10:14:36 pm
content: Quote from: Giovanni28 on September 30, 2015, 10:09:06 pmI was referencing Bryan's post #10 where he had already recommended looking at DC voltages:https://www.eevblog.com/forum/repair/crt-adjustment-tektronix-2465/msg760826/#msg760826Which then points you to the other thread. I was just saving a step.

author: Giovanni28
author_rank: Contributor
timestamp: September 30, 2015, 11:13:13 pm
content: I apologize MarkL.I think unmount all over again, to check the welds, welded components and if by chance I'm wrong in the assembly of something else.Is it possible that the change of the capacitors, involves a few problems of calibrations?How do I disable the CRT to make sure that does not come off, but I do voltage measurements?

author: MarkL
author_rank: Unknown
timestamp: October 01, 2015, 12:01:48 am
content: Changing the power supply capacitors shouldn't change your calibration.Do you hear relays clicking when the scope is turned on? Or do the front panel lights all turn on and then stay that way?Are any knobs or switches responding?I can't emphasize enough that the right place to start with a problem like this is to check the power supply outputs.

author: Giovanni28
author_rank: Contributor
timestamp: October 01, 2015, 12:19:12 am
content: Quote from: MarkL on October 01, 2015, 12:01:48 amI don't hear Relay clicking when the scope is turned on. Initially all the lights are not on.Any knobs or switches not responding.Although the picture of the display appears a very bright, it is actually a very short line very bright.How do I disable the CRT to make sure that does not come off, but I do voltage measurements?

author: Giovanni28
author_rank: Contributor
timestamp: October 01, 2015, 12:26:37 am
content: However I have not changed only the power supply capacitors, but also those of the motherboard A1.The oscilloscope worked well before replacing electrolytic capacitors on the motherboard.

author: MarkL
author_rank: Unknown
timestamp: October 01, 2015, 01:54:03 am
content: Quote from: Giovanni28 on October 01, 2015, 12:19:12 amProbably the easiest way is to turn down the grid drive on the HV supply card. Mark it before you move it so you can put it back.If this doesn't have enough range, you could disconnect the high voltage connection going to the CRT anode. Be careful since the anode will hold a high voltage charge.Alternatively, just get your voltage checks done quickly.

author: Giovanni28
author_rank: Contributor
timestamp: October 01, 2015, 11:52:31 am
content: Because before the replacement of electrolytic capacitors on the motherboard A1, tensions were the right ones and then instead should have been changed?

author: Giovanni28
author_rank: Contributor
timestamp: October 01, 2015, 03:07:57 pm
content: Somehow, I do not know why, but now the oscilloscope works perfectly! Great.

author: Giovanni28
author_rank: Contributor
timestamp: October 08, 2015, 10:18:18 pm
content: I sang victory too soon! 😂 Unfortunaltely, this evening I turned on the oscilloscope and the problem recurredQuote from: Giovanni28 on September 30, 2015, 09:10:52 pmI turned off and then turned back on and the problem has apparently disappeared.

author: Giovanni28
author_rank: Contributor
timestamp: October 08, 2015, 10:32:59 pm
content: 1) There is still something that I think should not be. Look at the following pictures. When I press the button beam find, this is what happens:2) If I put on CH1 and CH2 two sinusoidal signals both from 1kHz and 5Vpp, here is what presents itself to me. Is the phase shift normal?3) With the same previous configuration, in XY mode, this is the figure. As you can see is not perfectly circular.

author: guido
author_rank: Regular Contributor
timestamp: October 08, 2015, 11:11:42 pm
content: That is not good, they should overlap. In XY also, a line at 45 degrees.

author: Giovanni28
author_rank: Contributor
timestamp: October 08, 2015, 11:16:02 pm
content: Quote from: guido on October 08, 2015, 11:11:42 pmDo you have any suggestions?

author: guido
author_rank: Regular Contributor
timestamp: October 08, 2015, 11:38:01 pm
content: Check the supply voltages (always first thing on the list). Have one myself, it's a complicated beast. Had to fix several issues and replaced the supply caps.Suggest to get the service manual and start digging. There is also a tekscopes yahoo mail group with a lot of knowledge.

author: MarkL
author_rank: Unknown
timestamp: October 09, 2015, 02:29:43 pm
content: That's very strange. There's about 300us of delay or phase shift between the two channels.Is the delay the same at all input frequencies?Just to be sure, this is the EXACT same signal coming into both channels? The BNC cables are in parallel?As for the problem coming back, try to see if you can make it happen. Perhaps it's something mechanical.If it's still a mystery but it happens anyway, look at the power supply levels while it's happening. If those are ok, start looking at the processor troubleshooting sections. Verify the processor reset control is working ok.

author: grumpydoc
author_rank: Super Contributor
timestamp: October 09, 2015, 04:01:42 pm
content: QuoteI hate it when that happens - Imuchprefer to diagnose a fault and fix itThings are more likely to stay fixed that way.

author: Giovanni28
author_rank: Contributor
timestamp: October 09, 2015, 04:37:45 pm
content: Quote from: MarkL on October 09, 2015, 02:29:43 pmYou are right. I had not entered two signals in parallel. I apologize.QuoteFor the rest, I think you're right. I will have to disassemble again.Thank you, very much.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 05:53:48 pm
content: Quote from: Giovanni28 on October 09, 2015, 04:37:45 pmSo is it working correctly with them in parallel?

author: Giovanni28
author_rank: Contributor
timestamp: October 09, 2015, 07:30:54 pm
content: Quote from: FlyingHacker on October 09, 2015, 05:53:48 pmYes.

author: Giovanni28
author_rank: Contributor
timestamp: February 12, 2020, 09:23:03 pm
content: Eventually I managed to repair the oscilloscope.