Tektronix TDS640A needing help for repair please... - Page 1
Forum section: electronics / testgear

author: vehiculeselectriques
author_rank: Contributor
timestamp: September 11, 2025, 11:36:49 pm
content: Hello,i'm proposed for about 150$ a to be repaired Tektronix TDS640A (no floppy option though it indicate pass on test)unknown calibration or functions state, no option displayedit start up withFAIL - Acq/Proc interfaceFAIL - AcquisitionFAIL - Attn/Acq Interfacechanging hundred electrolytics is all it needs ?what value such scope now days ? upgrade possible ?what do you think ?thanks

author: temperance
author_rank: Super Contributor
timestamp: September 12, 2025, 01:03:09 am
content: I wouldn't buy any A models today unless you can inspect inside.In my TDS520A, the leaked electrolyte had eaten away the legs of some memory chips and the surrounding traces and vias on the PCB. The machine went as scrap.The B models are better because they use ceramic capacitors.

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 12, 2025, 01:45:46 am
content: $150, and in a best case scenario where it's not destroyed as described above, then you'll still need to invest time and money to recap everything to push off its inevitable demise.Or if you're okay with a 200MHz limit, for a few dollars more, you can buy a much better scope like the SDS804X HD.

author: vehiculeselectriques
author_rank: Contributor
timestamp: September 12, 2025, 02:03:26 am
content: thanks for your advisesi don't understand about 200Mhz SDS804X HD as it's a 70Mhz scope

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 12, 2025, 02:27:29 am
content: Quote from: vehiculeselectriques on September 12, 2025, 02:03:26 amA 70MHz scopefirmware restrictedon a calibrated200MHz platform. More information on how to improve it is on this website.

author: vehiculeselectriques
author_rank: Contributor
timestamp: September 12, 2025, 02:59:29 am
content: https://www.eevblog.com/forum/testgear/siglent-sds804x-hd-same-upgrade-scripts/

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 12, 2025, 05:34:46 am
content: I won't pay more than 5000yen ($50, whatever) for any TDS500 series or early TDS600 series scope.Here in Japan, a fully working TDS500 series scope that has passed a full performance verification with test report won't sell for much more than around 8000yen.The TDS500 C or D models, the better TDS600 series scopes and any decent TDS700 C or D series scopes in working condition are the ones that are worth buying.Unless you can get the earlier model scope for really cheap, then they are worth fixing if they don't have too much capacitor leakage.

author: vehiculeselectriques
author_rank: Contributor
timestamp: September 12, 2025, 09:53:28 am
content: thanks i wish having same second hand prices here, here these are expensive, everything isi will stay with my old Tektronix 2445B i repaired (thought still have to recap psu)and wait until i have some cash available for a "modern" solution, probably with integrated waveform generator.... which suit my cheap wallet way better than an old finaly too expensivecan of worms

author: nctnico
author_rank: Super Contributor
timestamp: September 12, 2025, 10:22:09 am
content: Quote from: vehiculeselectriques on September 11, 2025, 11:36:49 pmSTAY AWAY FROM THIS SCOPE!Work will include cleaning boards, resoldering components, fixing traces and fixing encoders because the electrolyte has dissolved all the coppper. And if (big IF) you get it to work you'll notice the scope is pretty much useless because it has no peak-detect and very short memory.Go for a TDS500 or TDS700 series. The ones from 1995 typically don't have the leaky capacitors (either due to using MLCCs or better electrolytic capacitors).

author: temperance
author_rank: Super Contributor
timestamp: September 12, 2025, 11:19:59 am
content: QuoteOnly specifying TDS500 is not enough. The important part is to get a B model like TDS540B,... Those and later models have ceramic capacitors. But this was already stated before.

author: nctnico
author_rank: Super Contributor
timestamp: September 12, 2025, 03:36:29 pm
content: Quote from: temperance on September 12, 2025, 11:19:59 amI have to disagree. I've seen a few of these scopes (500/600/700 series) from the inside and the later A models (say past 1995) have better quality electrolytics which don't leak.

author: vehiculeselectriques
author_rank: Contributor
timestamp: October 07, 2025, 02:07:46 am
content: Some news, i finaly bought it for a good pricestrange as there is no options indicated on banner infosi don't know if firmware is last one ?I don't know the manufacturing date but no capacitor leakage, all solders joints are shinyone screw missing and CH3- CH3 AUX1 output have been inverted on connectors...Strange looking screen culprit was found quickly, a fellow was brutal on ADG281 corner pinsafter some exacto knife action all is back to normalI mesured low voltage rails and checked culprits are some capacitors of which impedance is way too highhope the failed tests would be solved by bad caps replacement... waiting for parts now

author: vehiculeselectriques
author_rank: Contributor
timestamp: October 16, 2025, 11:49:35 am
content: recap is done with polymer tantalumAcq boardProc boardi checked and re checked but i only made it worstas now scope start, front panel leds lights on but screen stays black, the front panel lights off and then on the black screen only the scale at the top is visiblei don't find anyproblem with recap so i suspect this connection boardTektronix 671-2846-00 D1 BUS cage 8009some pins are not connected between these 2 connectors for processor and Acq boardis this normal ? i don't find pinout schematic of this board

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 16, 2025, 12:02:07 pm
content: I just checked one of mine and not all pins are connected through, including the ones you highlighted.

author: nctnico
author_rank: Super Contributor
timestamp: October 16, 2025, 12:02:42 pm
content: Quote from: vehiculeselectriques on October 16, 2025, 11:49:35 amThat is not a good idea. The design needs electrolytics in some places. Replacing with low ESR capacitors will cause problems. I'm also missing an ESD mat in the pictures.

author: vehiculeselectriques
author_rank: Contributor
timestamp: October 16, 2025, 01:30:39 pm
content: can you elaborate on "some places" please as i can redo but would prefer not all boardFor ESD i have taken care to hold the board on edges without friction moves and after touching earth ground to limit ESD, should be ok i think...here is video of screen at start upand 7segment display on processor boardwhat do you think ? seems to me processor board does not start ok(no display tests no clock image)

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 16, 2025, 03:41:39 pm
content: The two segments on the 8-segment display alternating like that indicates the scope at least thinks it had booted somewhat ok, as in there are no major failures that it found in the boot process that stopped it from booting.(For example, a number 8 often means the NVRAM data has been lost etc).Do you have a debug port adapter?

author: vehiculeselectriques
author_rank: Contributor
timestamp: October 16, 2025, 04:13:26 pm
content: thanksunfortunately this scope don't have option 13 board and i do not have debug port adapter,can i DIY make one ?

author: nctnico
author_rank: Super Contributor
timestamp: October 16, 2025, 04:59:36 pm
content: Quote from: vehiculeselectriques on October 16, 2025, 01:30:39 pmIIRC there is some circuitry on the acquisition board. In the TDS500/700 series there is an oscillator section on the acquisition board which (according to the info I have found) needs electrolytics.

author: vehiculeselectriques
author_rank: Contributor
timestamp: October 16, 2025, 05:22:18 pm
content: thanks if you find info on where is this oscillator section and which capacitors are critical to be electrolytique would help a lotOEM electrolyticspolymer tantalum replacementproblem(s) seems to be located in Acquisition bard as unplugging all 3 connectors to/from proc boardgive the same start up 7segment and scope screen results.to calm my nerves i recaped the front panel board, one smd axial pin led is toasted (channel 4), i not succeded finding replacement led ? that suits here, color seems to be yellow greenish ?