Tektronix TDS744A cannot boot completely - FlashROM Checksum - Page 1
Forum section: electronics / repair

author: desgriangmascho
author_rank: Newbie
timestamp: October 15, 2023, 10:32:13 pm
content: Dear all,I hope someone can help me. Tektronix Germany doesn´t want to support this old device and recommended to study "TDS 500B, 600B and TDS 700A Service Manual". And there I´m led to "Replace the A11 DRAM processor/display module".Here in EEVblog I found detailed and helpful information (author=radioguy123 link=topic=302663.msg3867140#msg3867140 date=1639181947), leading to FlashROM Checksum error displayed by this 7 segment display on the processor board.The scope worked fine last year, so I bought it and then didn´t use it for 15 months. I fear it forgot how to boot due to battery failure. The scope starts, front display LED are on, boot routines are done up to the last step "e FlashROM Checksum". There I get ".e" and boot process hangs. Front display stays dark, all LED of the keyboard stay on. I tried to attach my slow motion video clip of the 7-segment display messages - it´s not allowed here. If you want I can send it with an email. Or I´ll create a set of pics.So my question to you: Is there any option like a hidden complete reset or something like that to resurrect my instrument (besides "replace processor board")?Thank you in advance and kind regards, Stefan

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 16, 2023, 11:15:56 am
content: My first thought is the NVRAM chips need replacement due to low battery.There is a seller on ebay that has replacements.If you have lost all data, tekwiki has some files you can copy onto the new chips, or I can check if I have this model of scope tonight and copy the data out later with my chip programmer.https://w140.com/tekwiki/wiki/TDS744You'll need to use the correct version according to your scope version, use the latest of v1.x or v4.xIf you flash the wrong version it won't kill the scope, just flash the other version and try again.There's a Windows app to copy the data in and out via GPIB, or ypu can use a chip programmer if you are replacing the chips anyway.

author: desgriangmascho
author_rank: Newbie
timestamp: October 16, 2023, 02:46:21 pm
content: Dear TERRA,thanks a lot for your superfast response! You are right, the trouble cause most likely is low battery. And knowing what I have to search helped me to find good YouTube tutorials to replace NVRAM.But it seems that I´m a lucky dog: I forgot to switch off the mains supply in my lab. So obviously the batteries had time to charge a bit or it was just luck. I started my scope once more and it worked. The next tries failed again. So I´m confident that it has to do with NVRAM, but stored data should be still fine. I´ll try to open the cases and replace the batteries without desoldering the whole module. Hopefully that works, because neither I worked with GPIB programming nor with a chip programmer so far...As well I´ll look for a source to get NVRAM replacements or complete modules already programmed. BTW: If my scope doesn´t boot completely, can I talk with it via GPIB at all?I´ll keep you updated!Thanks again and kind regards, Stefan

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 17, 2023, 12:39:28 am
content: The batteries are integral to the NVRAM chip and cannot be replaced without the careful use of a Dremel etc.Some NVRAM chips can still be bought new on Digikey and Mouser, but the Watchdog/Timekeeper one with the RTC inside is completely obsolete, hence my suggestion of the reproductions from ebay.If you are handy with a mill (or really steady with a Dremel), you can machine off the top and expose the coin cells to solder in new ones, you can find xrays and pictures and guides around the net on this process.You can still talk via GPIB if it doesn't boot. I would suggest trying to read out the NVRAM data as soon as possible, if you get a good read, it will make your life easier.https://www.eevblog.com/forum/repair/unified-tektool-released-!-(firmware-flash-tools-for-old-tds-series)/msg3758918/#msg3758918Also, check your error log, see if it says anything there.Also also, do check the SMD capacitors on the acquisition and main boards (bottom and top respectively) for leakage, I'd replace them regardless as its a very well known issue.And also while you have it apart, check the PSU board for Rifa caps (4x 1000pf or 2200pf 10mm pitch caps IIRC) and replace, and check for the presence of capacitor C17 (47uF, 80V LOW-ESR electrolytic, feel free to increase voltage rating a bit) roughly around the center of the board if your board revision has it, replace it immediately too. It's for standby power and if it goes high-ESR, it takes out some TVS diodes and a transistor that kills your standby power so the scope won't turn on. As it is in use whenever the scope is plugged in even when turned off at the front panel, it's old now, it does need replacement...

author: Tantratron
author_rank: Frequent Contributor
timestamp: November 12, 2023, 11:18:06 am
content: Quote from: TERRA Operative on October 17, 2023, 12:39:28 amHelloTerra Operative,Could provide a picture where these specific components located, I mean the ones about the standby power sub-system ?Eventually you'll see pictures of my two PSU models and issues on this new threadhttps://www.eevblog.com/forum/repair/tektronix-tds500-tds700-power-supply-models-psu-repair/which I created recently.Thank you, Albert

author: TERRA Operative
author_rank: Super Contributor
timestamp: November 13, 2023, 01:32:45 am
content: I updated the PSU info in the other thread.

author: inlinebeginner
author_rank: Contributor
timestamp: November 13, 2023, 03:54:43 pm
content: Quote from: Tantratron on November 12, 2023, 11:18:06 amAgree.I just repaired two TDS744A and one TDS684A. The C17, 47u/80V needs to be replaced ASAP for all TDS744A, TDS684A, otherwise, it will cause the damage of Q9 (BU508A), VR4 (1.5KE220CA) and VR5 (1.5KE250CA) shortly. The reason is C17 ESR is too high, might over drive Q9, for a new cap C17, ESR<0.9 ohm, the one I saw ESR=18 ohm, which caused the damage of Q9, VR4, VR5. If C17 ESR is around 2 ohm, it might be still working, but don't wait, just change it ASAP. I paralleled 3 ceramic caps, each 22u/25V, total ESR 0.17ohm for the replacement of C17 47u/80V electrolyte cap, so far looks ok.If Q9, VR4, VR5 were damage, change C17 first, then replace Q9,VR4 and VR5, otherwise they will be damaged again at power on.Lin

author: Tantratron
author_rank: Frequent Contributor
timestamp: November 14, 2023, 12:54:58 pm
content: Many thanks Lin, so as I mention in the other threadhttps://www.eevblog.com/forum/repair/tektronix-tds500-tds700-power-supply-models-psu-repair/msg5168034/#msg5168034maybe I quick need to replace C17 or just focus on new PSU design which seems more reliable.

author: Tantratron
author_rank: Frequent Contributor
timestamp: January 01, 2024, 09:10:24 am
content: Quote from: desgriangmascho on October 15, 2023, 10:32:13 pmI had the same boot error, namely ".e" which means an exception then somewhere a memory content is corrupted (the processor attempts to execute an instruction but the instruction does not exist into the known assembly language).There could be different memories affected so you need to check after which boot phase the ".e" does occur. Phase 1, phase 2, phase 3.... to phase eIf there is a ".e" then it shows what part is in exception or failed the boot test.