Tektronix 2221a repair project - Page 1
Forum section: electronics / repair

author: Fractal
author_rank: Contributor
timestamp: May 07, 2021, 10:41:57 am
content: Hi!I just acquired my first analog scope to complement my Rigol 1052It's a Tek 2221a. Cosmetically apart from the dust it looks in good shape; no broken knobs or yellowing. Allegedly came from a school but picked up at a general electronics shop locally here in TaiwanFocusing appears fully functional too, as my research showed this was a recurring issue with these puppiesThen when I came to test it I noticed a couple issues;1- The screen membrane buttons don't work; a minor issue I thought, probably just a little oxidationBut 2- After a few minutes of jerking around the knobs, the OSD disappears! But traces remains visible somehow. Only the digital features seem to become inoperable....So obviously I told the shop it appears it's dead, but I'll take it for 30 bucks, which they agreed lolComing back home, the OSD was working again on powering up!Now the reason for this topic is that I can't quite figure out the origin of the problems...1-For the front button I cleaned the membranes and pcb, applied contact cleaner for good measure, but still no response on the interface2-I'm confused as for the origin of the OSD failure; it seems to come up after heating up a bit, but I don't think it's a PSU issue as the traces remain useable. There is not all that much dust either that could choke cooling that muchHas anyone had similar issue with their 2000-series scopes?Here are some pics:The interface, after the OSD diesHere with fully working OSD shortly after powering upAnd here the top guts because prettyThanks!

author: Fractal
author_rank: Contributor
timestamp: May 07, 2021, 12:59:40 pm
content: After some further investigation, I have now narrowed down the button fault to the flex pcb carbon pads; even after cleaning/sanding(on paper) and recharging with a pencil, no beansThere is some continuity between one 2 points of the same pad, but none from the pad to the pin.I might need to recharge the pads with some carbon paint or something

author: David Hess
author_rank: Super Contributor
timestamp: May 07, 2021, 10:37:54 pm
content: My experience is that the traces on the flexible laminated circuit board corrode to an open condition.The storage trace and on screen display are controlled by the same intensity control which allows the on screen display to be toggled off and on by turning the control fully counterclockwise.

author: Fractal
author_rank: Contributor
timestamp: May 08, 2021, 01:42:43 am
content: Thanks for your response DavidAre those Tek flexibles commonly afflicted by this issue? What's the best course of action to bring them back to a functional state?I have noticed that flicking the screen intensity dial down to none allows enabling/disabling the OSD, but this is something different; when it goes off, I can't turn it back on again with this controlBesides, I had a new issue while letting it run open, attempting to see if it could be a heat accumulation issue.... IT FREAKING BLEW!Something from the PSU area blew off; white smoke, big bang, but the screen was still showing... Probably a bypass cap?You can see a bit of it next to the main switch.Looks like it came from whatever is hidden under the power socket

author: bdunham7
author_rank: Super Contributor
timestamp: May 08, 2021, 03:15:52 am
content: The button problem will likely be open circuits in the flex ribbon. I fixed mine with a CircuitWriter silver paint pen.Your explosion was likely RIFA madness. (Google it)As for the OSD, what happens if you run it in 'STORE' mode? Fix the RIFAs first, but then try the 'STORE' mode without twiddling any of the intensity knobs.

author: David Hess
author_rank: Super Contributor
timestamp: May 08, 2021, 03:27:04 am
content: Quote from: Fractal on May 08, 2021, 01:42:43 amThey very commonly fail. Some people have laid out new ones and had them produced. It is of course the same part as on the 2232 and 2224.QuoteMy guess then is a lose connection between the z-axis signals at the CRT and the vector graphics board. I do not remember but there may be separate connections for the storage and on screen display intensity signals. The schematics will show it and you can use the 2232 service manual which should be easier to find. Reseating the connectors to the vector graphics board may fix it but access can be tricky because of how it is assembled.Update: another thing which might cause it is a dirty or intermittent poteniometer. If the intensity control momentarily disconnected, the CPU might interpret that as a turn fully counterclockwise causing it to disable the on screen display until toggled back on again.QuoteThat was probably a RIFA X or Y class paper line capacitor. Those should be replaced if you gain access to them but they are not needed for operation.

author: Fractal
author_rank: Contributor
timestamp: May 08, 2021, 06:31:07 am
content: Well that RIFA suggestion was bang onThere only appears to be one across the board. All the electrolytics I could see looked fine too.it's a 28nF, I believe I found amodern KEMET equivalent on mouserNext step then would be to order a replacement along with conductive paint, and meawhile remove the front panel so I may refurbish all the pots with contact cleaner; some are a bit glitchy indeed

author: David Hess
author_rank: Super Contributor
timestamp: May 09, 2021, 12:39:52 pm
content: Quote from: Fractal on May 08, 2021, 06:31:07 amThat link does not work for me but the value is not critical as long as the proper type of capacitor is used. When selecting replacements for parts like that, I usually start with the lead spacing.QuoteWith burned traces, I use wire and solder to effect repairs.The potentiometers may recover with deliberate working. They can be disassembled to gain access to the resistive element and wiper but the work can be delicate.

author: Fractal
author_rank: Contributor
timestamp: May 09, 2021, 01:35:01 pm
content: Well, I just found a silver conductive ink pen and a similar specced cap at my local electronics shop of all things!Idk what's going on with that link; here's the direct link to datasheet; it's also a paper dielectrichttps://www.mouser.com/datasheet/2/212/1/KEM_F3011_PME271M_X2_275-1101254.pdfHowever the one I found is something else, although it appears to show similar characteristics? It's a PP film from Carlihttp://www.sjohm.co.kr/products/img/pdf06.pdfI guess I will just send it and find outI wish it were easier to solder a wire on a flex cable with those contacts; as you may have seen on the pic above I applied the paint already, will see how that goes

author: David Hess
author_rank: Super Contributor
timestamp: May 10, 2021, 04:31:16 am
content: Quote from: Fractal on May 09, 2021, 01:35:01 pmI tried using conductive "glue" to fix one of mine but it was just not practical.

author: Fractal
author_rank: Contributor
timestamp: May 13, 2021, 09:20:58 am
content: Hello!Update time:I managed to fix the flex ribbon using the conductive silver pen! All keys working perfectly againSuccessfully replaced the RIFA capacitor; seems goodFully cleaned up the front face, knobs and contact lubed the pots and buttons as much as I could without removing the front panel (requires taking the whole damn thing apart; don't want do do it yetEverything is working great now, apart from a couple remaining issues....The edge-lit incandescent bulbs broke after too much manipulation...I measured the voltage on that bulb and it goes up to 30V. Picked up a pack of 24V 5mm bulbs from the shop, but the light is too damn weak... Any idea on what bulbs should get in there?The power... Before reassembling the shell it did run perfectly for an hour; no more OSD disappearing, all good. Since I recased it though now the whole screen goes down after about 15mins of running...I'm guessing this could be a thermal shutdown thing? Any ideas? I did clean the PSU and fan, it's extracting the heat out just fine... the Sensor is also placed properly where it was, right in front of the fan.Any pointers for that recurring issue?Thanks!

author: bdunham7
author_rank: Super Contributor
timestamp: May 13, 2021, 02:09:45 pm
content: I don't recall the bulb number, but the bulbs are wired in series, so take that into account. If you have one remaining that didn't break, you can put a bench PSU on it and see what it takes for voltage and current.As for the other issue, take the case back off and see if it works. If you can get it to run consistently without the case, then you likely do have a thermal issue, but possibly not in the power supply.

author: David Hess
author_rank: Super Contributor
timestamp: May 14, 2021, 01:56:49 am
content: The two series connected graticule illumination bulbs are Tektronix part number 150-0077-01 which is 14 volts, 0.08 amps, wire leads, #2182D, T1-3/4.https://www.mouser.com/ProductDetail/JKL-Components/2182?qs=gp8goBkfC5Ha6gzQzENy6Q%3D%3D

author: Fractal
author_rank: Contributor
timestamp: May 17, 2021, 09:15:55 am
content: Hi!So I'm glad I managed to get the brownout issue on camera.This time I turned it on, left it there to measure the ripple on some PSU, and after a while ~10mins the OSD disappeared, then a few mins later the whole screen went off.I let it run anyway and surprisingly everything came back up!...Except not very consistently...In that video you can see the screen flicker then die then come back finally without OSD...Note: the reading difference came from my probing points that moved.Any pointers now? Thanks!

author: David Hess
author_rank: Super Contributor
timestamp: May 17, 2021, 04:33:30 pm
content: I do not see the deflection changing so the problem is not with the high anode or cathode voltage. It might be a problem with the z-axis CRT circuits some of which operate at high voltage. It could also be a problem with a loose connection between the z-axis CRT circuits and the intensity control circuits.Does the entire screen blank out when in analog mode and the on screen display is active?

author: Fractal
author_rank: Contributor
timestamp: May 17, 2021, 05:09:26 pm
content: I see; well it's a fully intermittent issue regardless of the store/non-store modeSometimes only the osd disappears, sometimes both osd and traceYou can notice the trace coming back without OSD towards the end, in analog fist then in store mode (as confirmed by the "T" trigger marker

author: David Hess
author_rank: Super Contributor
timestamp: May 18, 2021, 02:24:37 am
content: Quote from: Fractal on May 17, 2021, 05:09:26 pmThat makes me think the problem is with the intensity control potentiometers or the connections to them.

author: Spawn
author_rank: Frequent Contributor
timestamp: January 27, 2023, 02:15:02 pm
content: @Fractal, I know this is almost two years ago, and it looks like you didn't find any solution to OSD issue.I didn't use my 2221A for a while, but last week when I needed it, I had same issue with OSD disappearing, maybe little bit different issue than yours, on my 2221A the whole screen goes blank after +/- 8 minutes usage, when I turn it off and on again, the analog part starts working but not the storage part anymore, I had to wait till it was cooled down to get OSD working.That's why I ended up in your topic here, and I think I found a solution (at least on my 2221A)After checking the service manual, the OSD is running through a Display Controller chip (U9208), the only chip with a heat sink on the storage board (if you can call that a heat sink ofc).I took a temperature measurement with open case, in my fairly cold hobby room (16 °C), after 30 minutes the temperature on the heat sink raised up to 42 °C and stayed around that after 2 hours testing, the OSD didn't crashed with open case, the chip should handle that easily, but the measurement was on the heat sink and not directly on the chip itself and the case was removed, I think after a while things get old and the chip can't handle the heat anymore, or maybe the thermal paste between the chip and the heat sink dries out. I couldn't find a way to remove the heat sink without damaging the board, so I didn't touch that.I thought, why not put another heat sink on top of the existing heat sink and see what happens, I didn't have any matching heat sink, the original one is 30mm round, but I had some Rasberry Pi 4 heat sink sets and some of them are 15x15mm square, I put 4 of those on the existing heat sink and put the case on.I did a 3-hour test run in storage mode to make sure that the display controller got used and OSD didn't crash anymore, it looks like the issue was the chip getting too hot, I am not sure if it helps with your 2221A, but you can try.Just be careful when you use a heat sink, make sure it is not higher than 4mm otherwise it will hit the case, and also make sure you have a good heat sink with strong thermal double-sided adhesive tape on it.Disclaimer: I won't take any responsibility if something goes wrong, it is up to you if you want to try or notHere after 2 hours testing:Heat sinks on top of the original heat sink:After 3 hours testing with case on 2221A, still working without issues:A side note: I did remove the pouch from the case, it looked cleaner to me on the bench without the pouch, I am not sure if removing the pouch also helped with heat escaping.

author: David Hess
author_rank: Super Contributor
timestamp: January 27, 2023, 11:12:13 pm
content: Those oscilloscopes just look so cool.

author: Fractal
author_rank: Contributor
timestamp: January 30, 2023, 02:42:00 pm
content: @Spawn Wow what a mint unit you got yourself there!Well damn, for nearly 2 years I've been banging my head against the wall trying to fix it and looks like that just did it!A huge thanks to you for digging that up and taking the time to share your findings.Not even in this forum but last year I posted about it on reddid, someone linked me to the actual service manual of that model and I went down the rabbit hole of checking the power rails, suspecting a short could be causing the overheating.Found out my +5 test probe gave 0, and my -5 was inverted to +5 ?!Couldn't find the source even after unplugging the digital board, purchased a freakin IR cam with znse lenses to 3D print a macro adapter, couldn't find a very concerning heat source.Anyway, I took your lead and went one step further,The OSD chip heatsink mount bugged me too until I figured the trickI used a thin flathead driver to pry the clasp off using the tabs made for itI was expecting to see some old dried-up thermal compound, but was quite surprised to find none at all!Beautiful ceramic chip nevertheless; So I just slapped a thin thermal pad on there, closed it up and what do you know, it's been heating my lab for well over 4 hours!Super pleased to finally have it completely cleaned up, fully working and dependably soWe'll see how it holds up in summer though, but for now I'm blessed.It finally gets to join its lads on the test tower (of cheap second hand test equipment);@David Hess those look great! is the 2230 mostly just a dual timebase sibling of the 2221?I had a chance to get a 2465B for an alright price but figured man the digital part of these makes it so much more useable and versatile

author: David Hess
author_rank: Super Contributor
timestamp: January 30, 2023, 04:18:10 pm
content: Quote from: Fractal on January 30, 2023, 02:42:00 pmYes, that is correct, although I have in my notes that there were two versions of the 2221 with one being 60 MHz and the other being 100 MHz. The 2221 is a single timebase version of the 2230, and the 2221A is a single timebase version of the 2232.The 2221/2230 and 2221A/2232 have very different storage and user interface designs. The 2221/2230 use an analog channel switch to digitize both channels with a single ADC, like the 468 which preceded them, while the 2221A/2232 have a dedicated ADC for each channel, and then select which samples to save with a custom digital multiplexer IC.QuoteI have a 2445 variation now, and have had a 2247A for a long time, but it is the 2230/2232 that I prefer because of the storage which works so well. Of course the analog only oscilloscopes are useful for their automatic measurement capabilities.

author: Spawn
author_rank: Frequent Contributor
timestamp: January 30, 2023, 06:37:02 pm
content: Quote from: Fractal on January 30, 2023, 02:42:00 pmThank you, I got it11 years agofrom a retired engineer, it is mint conditionThe pictures are gone in that topic, thanks to photobuckets new policy'sQuote from: Fractal on January 30, 2023, 02:42:00 pmI am really happy it worked for you too, thanks for reporting back!Quote from: Fractal on January 30, 2023, 02:42:00 pmGreat to know that, thanks. I didn't want to damage anything, but like you said if it acts up again in the summer, I will take the original heat sink off and maybe make a new heat sink on my milling machine and use a good quality heat sink compound.Quote from: Fractal on January 30, 2023, 02:42:00 pmNo heat sink compound!?! No wonder it went wrong, another thing is, first I found your topic here, and searched all over the internet, but only two of us had this issue, that is weird, or did Tektronix forgot to put thermal paste on our units only?Quote from: Fractal on January 30, 2023, 02:42:00 pmHave fun your 2221A! I used it for a couple of hours yesterday and I love it.Did the diagnostics while I was on it:Channel 1:Channel 2:

author: Fractal
author_rank: Contributor
timestamp: January 31, 2023, 04:10:33 pm
content: @Spawn Well damn, if it was good for a retired EE surely it's good for meMan this thing is amazing, just discovered the rolling acquisition mode in store for speeds >1sec and it's brilliant, that could totally work with digital signalsWell let's look into the thermal paste thing, what's your serial number? mine says B012143 on the backDid you ever replace the rifa btw? Mine was the first thing that blew up when I got it

author: David Hess
author_rank: Super Contributor
timestamp: January 31, 2023, 07:57:39 pm
content: Quote from: Spawn on January 30, 2023, 06:37:02 pmI doubt the original design used thermal paste. That heat sink does not really have a low enough thermal resistance to require it.

author: Spawn
author_rank: Frequent Contributor
timestamp: January 31, 2023, 10:58:08 pm
content: @Fractal, Serial number on my Tek is H700582, the latest date I could find on the components was December 1992, so I think it is made in 1993. The serial numbers are far off, I think David Hess is right about the thermal paste not being used.I also replaced 3 RIFA's last week, the big one and two in the net filter, I checked the RIFA's after reading your post about blown RIFA, all 3 were not blown, but I saw small cracks on the housing. The case was already open since I was checking the thermal issue, and we have an electronics shop nearby, they had the right values, the new small ones for net filter had bigger housing, so I had to make a bridge to the new capacitors. I didn't want to wait till they get blown, better be safe than sorryIt is indeed a nice scope, I don't use it often, I was thinking about to get a new digital one next to 2221A, but that would be a waste of money, I have a lot of hobbies, so I can use the money somewhere else. The 2221A is more than enough for my needs.And it fits nicely between my outdated stuffQuote from: David Hess on January 31, 2023, 07:57:39 pmI think you are right David, I also think it is more a clamp to hold the chip in there, and its second job is being a heat sink, but it does a lousy job at doing that, at least on our units, keeping the chip cool solves the OSD crashing problems.Or, like I said before, maybe the chip gets hotter when the components in the scope gets older.

author: Gianni
author_rank: Contributor
timestamp: April 03, 2023, 11:16:50 am
content: Hi Guys!I noted too late this thread and some weeks later I went thru the same story and arrived to the same conclusions about heat (I also had strong battles with the 2221 power supply and 2230, that was even incomplete; eventually it seems that I won)I just wish to add a bit: in my case, even after having added the thermal paste, the problem went on. The cause was that the previous owner didd reverse the fan. In this way the U9208 was heated by all the heat produced inside the oscilloscope, instead of being refreshed by incoming air.Reversed the fan, the problem disappeared.

author: calibrationfixture
author_rank: Regular Contributor
timestamp: July 28, 2023, 07:25:14 pm
content: Hi to All,@ to Reply #25:Same story with my 2221A and a 2232 of a friend. Fans are blowing to the insides. Both Scopes didn't run into trouble. But a recently serviced 2245A ran into trouble with its reverse mounted fan. After approximately 30 minutes it shuts down. Also its enclosure feels "warm". According to its Service Manual (070-6557-00 Page 2-2) air must be exhausted from the right-side ventilation holes. After the reversing the enclosure stays "cold" and no more powering-offs.Calibrationfixture

author: David Hess
author_rank: Super Contributor
timestamp: July 28, 2023, 09:17:45 pm
content: One of my 2232s just started acting up. I will be checking the thermals first and heat sinking some of the ASICs.

author: Allen49
author_rank: Contributor
timestamp: February 01, 2024, 02:33:36 pm
content: I have a Tektronix 2221 that I am trying to repair. The previous owner stated he was using the scope when he heard a pop and something started smelling burnt. I found that R909 was burnt and also one of the legs on Q9070, IRF710, was burnt off. The IRF710 was placed on a heat sink with a piece of heat sink tape but I don't know if it was ground through the center pin to the heat sink. Could anyone help me out with this.

author: David Hess
author_rank: Super Contributor
timestamp: February 01, 2024, 04:22:37 pm
content: The tab is the drain and *must* be insulated from the chassis.If the MOSFET is blown, then the gate driver around Q908 and switching controller U930 are probably damaged. The entire circuit needs to be checked.I know of many examples of that power supply having failed in that way but never had one to diagnose why.