Tektronix TDS 754D: firmware fixed, bad display - Page 1
Forum section: electronics / repair

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 14, 2025, 12:56:55 am
content: I was given a broken Tektroix TDS 754D scope recently. It stopped booting on the previous owner an number of years ago.I found that the batteries in the two Dallas battery-backed SRAM ICs were dead. I performed surgery on them to replace the battery, however that left me with a scope that has two blank SRAM ICs and no firmware.I am attempting to follow this thread:https://www.eevblog.com/forum/repair/unified-tektool-released-!-(firmware-flash-tools-for-old-tds-series)/ However I am encountering some problems. I bought a National instruments GPIB-USB-HS adapter on ebay, I am not sure if it is real or not but all the NI software seems to work correctly.Whenever I try to run a tektool command in cmd it says: Error : Unable to clear deviceibsta = 0x8100 iberr = 14 (EBUS)Cleanup: Taking device offlineI dont know what I am doing wrong or what this error means. This forum thread I mentioned is very confusing to me, there are users talking about different versions of tektool and also a tekfwtool?If anybody has had any experience with tektool I would really appreciate some help. If it comes to it I have computers with older operating systems at my disposal.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 14, 2025, 01:07:18 am
content: I do also have a Xgecu Pro T48 EEPROM programmer, so if somebody is able to get binaries of the DS1489 and DS1250Y on a TDS7xxD that may also work?

author: squadchannel
author_rank: Frequent Contributor
timestamp: September 14, 2025, 01:51:33 am
content: I have the dump for my 754D's DS1250. I looked for the DS1486 dump but it seems to be missing.I'll try it since it's disassembled and sitting around right now.But if the NVRAM is properly installed, it should boot even if it's empty (I might be mistaken).something else might be wrong. there's a mode you can enter by toggling the dip switches that allows detailed diagnostics, so it's worth trying.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 14, 2025, 03:00:07 am
content: Thanks for the reply! I am aware of the diag mode enabled by the dip switches, annoyingly it only seems to be referenced in the troubleshooting flow chart and not many details are given. I have tried using this mode but the 7-segment display is always fully lit from the moment the device is powered on.Before I removed the Dallas ICs to repair them the 7-segment display would cycle through a few numbers before settling into an alternating 8 - 6 - 8 - 6 pattern, somebody on the forum said that this happens when the DS1489 is missing. I assumed that by removing the Dallas ICs and replacing their batteries I had destroyed what little functional data was left on them. Hopefully the data on the flash chips is not corrupted.

author: squadchannel
author_rank: Frequent Contributor
timestamp: September 14, 2025, 03:10:21 am
content: For early TDS754D. The DEMUX on the acq board is not BGA, and the firmware version is 6.x or earlier.DS1486Y can be read and written using the DS1245Y. However, verify will it an error. because it has an RTC.calibration data for the 7xxD is stored in the EEPROM on the acq board, so you don't need to worry about it. only non-critical data such as SPC is stored in the NVRAM.For more details, ask @madao and @TERRA Operative.PS:I compared it with previously dumped data, but the data didn't match. Since it boots up, something seems different. GPIB becomes available, options should be able to be added, so customize it to fit your machine.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 14, 2025, 03:43:22 am
content: Thank you for the binary files! Unfortunately it did not make any difference, there is still a problem. I wonder if I damaged one of the Dallas chips during surgery, causing a problem on the processor bus or something.Where exactly is the firmware stored? is it in the two intel flash chips near the processor? Also my DEMUX on the acquisition board is not BGA as well, date codes I can find are late 1999 or early 2000.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 14, 2025, 06:56:00 pm
content: Progress! it turns out that I left a screw loose under the cpu board, causing a short. After fixing this the scope sprang to life!The firmware version is 7.1.1e, according to TekWiki there is a 7.4e version, however I don't know what is different between the two versions or if it is worth the effort + risk of upgrading. For now I am inclined to leave well enough alone.The next big thing I need to tackle is the internal display, it is very dim. The display is working and looks nice and sharp, so I doubt there is a digital or tube issue. Intensity is set to maximum in software, si I need to see if there is a hardware intensity control anywhere.

author: squadchannel
author_rank: Frequent Contributor
timestamp: September 14, 2025, 07:53:11 pm
content: Quote from: Alex_Baker on September 14, 2025, 06:56:00 pmI've heard that 7.x and above only work on later models, the BGA DEMUX.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 14, 2025, 09:07:01 pm
content: Quote from: squadchannel on September 14, 2025, 07:53:11 pmThis is interesting, I may be looking at the wrong ICs on the acquisition board, but the scope passed all self tests, unless the incompatibility shows up some where else. I attached a picture of my scope.

author: squadchannel
author_rank: Frequent Contributor
timestamp: September 15, 2025, 12:57:49 am
content: your 754D is a later model. The ADG439B DEMUX is BGA. early models used QFP.earlyhttps://w140.com/tekwiki/wiki/File:Old_TDS754D_acq.jpg

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 15, 2025, 06:20:37 am
content: Once the scope is working, firmware update is easy using the tektool. It just takes ages to load (like half an hour or more... be patient!)I never looked deep to see what boards are compatible with what firmware, besides sticking to the same major firmware revision.i.e. v7.xx can update to any v7.xx firmware, but v6.xx cannot update to v7.xx etc. There may or may not be exceptions to this, but I've never had a problem sticking to the same major firmware revision.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 15, 2025, 05:30:56 pm
content: I need to try tektool again now that the scope is actually running. It would be nice if there was a real step-by-step guide on how to do it somewhere, the forum post can hard to follow.I will not be able to work on the scope until this coming saturday, but I will look forward to it!

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 16, 2025, 04:30:56 am
content: Did you see my post here? It's more step-by-step than the OP.https://www.eevblog.com/forum/repair/unified-tektool-released-!-(firmware-flash-tools-for-old-tds-series)/msg3758918/#msg3758918

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 16, 2025, 06:53:03 pm
content: I did see your post, thanks TERRA Operative.Assuming I have the gpib adapter drivers installed correctly, are there any specific configurations required for tektool? Like gpib address or bus timing?

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 16, 2025, 11:08:02 pm
content: I've never had to do any config settings in Tektool. I use the Keysight adapter and software as per my guide, and as as long as that software can see the scope, the tektook 'just works'.I assume if your gpib adapter can see the scope it should work too.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 20, 2025, 10:05:21 pm
content: Today I tried messing with the adjustments on the side of the scope to see if I could bring back any brightness. By maxing out the brightness and contrast I could get a decent bit of brightness back, however it got very fuzzy and is unusable that way, not to mention wrong.I took a look at the crt board, it is covered with little unmarked potentiometers. With no schematic I don't know if any of them are useful.So my question now is what would cause a dim crt, bias? accelerator voltage? I am pretty certain that the tube is not burnt from use, the scope is spotlessly clean inside so no dust buildup from hundreds of hours of use. Also I think the color shutters are working ok, color is produced when the display is barely visible.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 21, 2025, 04:36:56 am
content: Here's a picture I just made with a description of the adjustments for the colour CRT board.There may be a few differences depending on your PCB revision, but this is most of the main adjustments.There is a chance you may have aging electrolytic capacitors, replacement might help... Or you could go for an LCD replacement. I'm currently working on that now, I'll release the design one the FPGA firmware is finished.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 21, 2025, 01:48:47 pm
content: The CRT board on my scope is a bit different than that one, the flyback is sitting horizontally above the pcb instead of mounted directly to it. Despite that it appears all the adjustments are in the same places and labeled with the same reference designators.I am not sure how to approach this at the moment, the CRT board is quite buried in the scope and is covered by the cpu board when it is installed, making any adjustments while powered up impossible.I would love to do a LCD upgrade, but I cant spend that much money on one right now.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 21, 2025, 01:57:28 pm
content: I usually remove the CRT and driver board, reinstall the cover plate and top PCB, then sit the CRT and driver board on top with a bit of cardboard or rigid plastic as an insulator.That lets me tweak the trimpots to my heart's content.Just be very careful with the HV trimpot, you can easily blow things if you adjust that wrong, so best to leave it well enough alone.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 21, 2025, 05:00:46 pm
content: That is a good call, it looks like the wiring is long enough to do that once the crt is excavated from the chassis.

author: Tantratron
author_rank: Frequent Contributor
timestamp: September 21, 2025, 05:13:34 pm
content: I'm sure you know this already but just in case, make sure to first chassis discharge the HT linking CRT's anode prior removing the CRT to proceed with an external display servicing. Otherwise this could be lethal hazardous shock to human body.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 22, 2025, 09:19:41 am
content: And use a wire with alligator clips etc to connect the metal frame on the CRT to the scope chassis, or just position it so the metal is touching.Also, maybe from one of the two plated screw holes in the middle of the board for good measure too.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 27, 2025, 06:52:51 pm
content: Thanks for the tips everybody, at this moment I have extracted the tube and display pcb and set it up in a way that it can all operate normally. This allows access to both sides of the pcb and all the internal adjustments.Now to figure out what to test.....

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 28, 2025, 04:57:14 am
content: I'd start with checking an replacing electrolytic capacitors. At least test them if you don't just replace them all wholesale.If you really need, I have some spare CRT boards, but would have to check postage costs, might come to US$30 or so to send to USA at a wild guess...

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 28, 2025, 02:49:46 pm
content: I suppose there is not much to do other than to check caps like you mentioned. Thanks for the spare parts offer, I will keep that in mind.While deciding what to do with the display I upgraded the scopes firmware to version 7.4e, it went well. After that I wanted to see if I can enable more options , 2M or 2C. Interestingly I had to enable option 13, I suppose it is not enabled by default on the firmware image that I used.I was able to successfully enable option 13, however I tried twice to enable 2M and 2C but was not able to get them to stick, I am not sure why this is happening.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 28, 2025, 04:05:50 pm
content: A D model scope should have the memory available for the 2M option. The image you posted above shows the latest of the acquisition board types and definitely has the 2M RAM installed.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 28, 2025, 04:42:33 pm
content: I figured as much, but I cannot get option 2M or 2C to take. I am getting expected responses from the instrument in the terminal when sending other gpib commands, so it seems that communication is working, the scope just wont accept option settings.I may try reverting to the original firmware to see if that makes a difference, it is unfortunate that it takes 45 minutes though.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 28, 2025, 06:14:00 pm
content: I put FW 7.1.1e back on using the backup I created when installing 7.4e, still not able to enable options.I thought that I was able to enable option 13 after installing v 7.4e, but that could have been a red herring. GPIB commands "*IDN" and "ERRLOG" return expected information to the GPIB terminal, communication is not a problem.perhaps there is a problem with my process or syntax?-Turn scope on and let it boot-set protect switch to unprotected-enter the device communication window in national instruments MAX program-send *IDN, scope responds with make, model, and firmware version-send PASSWORD PITBULL-send WORDCONSTANT : ATPUT 327695,1 (option 2M)-send ERRLOG?, scope responds with a warning about external VRAM access as expected-send ERRLOG CLEAR-send ERRLOG?, no errors present-exit device communication window-set protect switch to protected-restart scopeI should note that I am unsure about actuating the protect switch while the unit is booted up, I saw it done this way in a guide online. If I set the switch to unprotected mode before power up the scope does not boot and does not show up in the national instruments MAX program. This is interesting because tektool works in this state, meaning that gpib communication is established, however I can't use the device communication window in NI MAX. Something called VISA test panel is available in MAX all the time, but it is not quite the same and does not seem to be able to read responses from the scope.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 28, 2025, 10:32:16 pm
content: Your process is correct. The protect switch can be used after booting the scope, this is described in some of the manuals so it's all ok.Switching the protect switch before turning the scope on essentially puts it into a 'bootloader' type mode.When you send the command to enable the option, are you sending:Code:WORDCONSTANT : ATPUT 327695,1 (option 2M)OrCode:WORDCONSTANT:ATPUT 327695,1The second is correct.Note the lack of spaces around the colon between WORDCONSTANT and ATPUTCut and paste the commands directly from this thread to be sure you get them 100% correct:https://www.eevblog.com/forum/testgear/enabling-options-in-tektronix-tds500-tds600-and-tds700-series-scopes/

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: September 28, 2025, 10:57:53 pm
content: I suppose that would do it, thanks for spotting my error. In the guide I was looking at it really looked like there were spaces.Unfortunately I won't be able to test this until next weekend, the scope is all taken apart to test caps on the display board. I did not find any obviously bad ones, there was a handful very close to being out of the general 10% spec. ESR was all over the place but I find that it is hard to trust those numbers.I suppose it is possible that the CRT is worn out, but I really doubt it.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 29, 2025, 04:12:47 am
content: I will have some spare CRT's too in a while, once my LCD conversion is finished.. sometime....But, shipping..... that might be expensive...

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: October 04, 2025, 04:25:37 pm
content: I was successful in enabling the options 2M and 2C once I fixed my syntax error.I don't know very much about other than CRTs except that they can be a health hazard. So I don't know all the things that can cause a dim CRT, I do know things like wear or low HV can make it dim, but what about grid or screen voltages on the tube?