Tektronix TDS 820 - Page 1
Forum section: electronics / repair

author: dgimb
author_rank: Newbie
timestamp: August 07, 2024, 12:11:46 pm
content: Hello folks.I bought a Tektronix TDS 820 for repair.The main screen is dark, but the segment indicator on the motherboard runs.After connecting to the debug console port, I have the following log:-------------------------------------------------------------------------------------------------Int VBootrom Header Checksum passed.Bootrom Total Checksum passed.BootRom Check Sum passed.Bus Error Timeout test passed.Kernel Diagnostics Complete.Calling SDM (monitor) Routine.Enabling Bus Control register. Value = 0x67IMR 1 Register test passed.Misc. Register test passed.Timer Interrupt test (Auto-Vector) passed.NVRam DSACK FAILED, wrote 0x12345678, read 0x78ffffffNVRam DSACKS test failed.-------------------------------------------------------------------------------------------------Also I replaces DS1245Y to new one but the result still the same.I am also interested in whether it is necessary to flash the DS1245Y memory after replacement to new one.What exactly firmware need to upload in the DS1245Y memory?Also on eBay i found diskettes for my oscilloscope model...I'm curious about the left one on the photo.... what does the "Оptions key" mean?Thanks!

author: TERRA Operative
author_rank: Super Contributor
timestamp: August 10, 2024, 09:57:48 am
content: All options can be unlocked via GPIB, the procedure is around the various forums.You will need to program the new NVRAM, try pulling the data out of the old one, otherwise you might need to get a copy from a good unit if your old one has lost its data.

author: dgimb
author_rank: Newbie
timestamp: August 11, 2024, 11:06:55 am
content: Solved!The problem was that there was no signal on the data bus from the buffer chip (CPU data bus).This was the reason that the communication between the CPU and the NVRAM was not working properly.The reason is that the signal line in the inner layer of the PCB was broken.Thanks!P.S: Also, earlier (before the real cause of the problem was found) all data was extracted from the old NVRAM and loaded into the new one, but the result was the same.For now, the oscilloscope starts up and works correctly.

author: dgimb
author_rank: Newbie
timestamp: August 20, 2024, 12:32:38 pm
content: The memory of the DS1245Y may be empty at startup (erased before installation).The DS1245Y only stores the calibration data in my oscilloscope model (TDS 820).

author: TERRA Operative
author_rank: Super Contributor
timestamp: August 20, 2024, 02:08:35 pm
content: I think you will probably find that the calibration data is stored on some EEPROM's on the acquisition board, it's where the cal data is stored for the 500, 600 and 700 series scopes (I could be wrong about the 800 series though, I haven't played with an 800 series scope directly).The DS1386 (or equivalent) 'Ramified Timekeeper' or 'Ramified Watchdog' holds firmware and the DS1245Y (or equivalent) is the NVRAM that holds user settings, captured waveforms and option unlock data etc. There should be no actual calibration data in there.

author: dgimb
author_rank: Newbie
timestamp: August 20, 2024, 05:01:40 pm
content: Thanks for the advice.I'm going to backup the oscilloscope firmware and use the "NI GPIB-USB-HS" adapter to do it.Can you give me some information about this process?What are the important points here?Thanks!

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2024, 09:47:52 pm
content: Quote from: dgimb on August 11, 2024, 11:06:55 amWow, how did you figure that out? I might have checked every address and data line at the NVRAM for activity.

author: dgimb
author_rank: Newbie
timestamp: August 21, 2024, 12:40:38 pm
content: Quote from: David Hess on August 20, 2024, 09:47:52 pmThe falling edge signal of DIR signal was wrong.The reason was not signal on the RD*\1 pin on U1178.Please see attached image.

author: David Hess
author_rank: Super Contributor
timestamp: August 21, 2024, 03:47:01 pm
content: Quote from: dgimb on August 21, 2024, 12:40:38 pmSo with none of the buffers producing the correct output, something earlier in the logic was the problem.I would not expect that kind of output from any TTL gate because open inputs usually pull high, but FAST TTL has a lower high level input current.

author: TERRA Operative
author_rank: Super Contributor
timestamp: August 21, 2024, 04:15:42 pm
content: Quote from: dgimb on August 20, 2024, 05:01:40 pmHere's the instructions and tektool DOS app attached (Can be run from command prompt in Win10).Also info on unlocking options too.I've also added some floppy disk tools that will allow you to copy in and out the NVRAM and Calibration data (To backup your cal data. I have seen the EEPROMs go bad once or twice).Be very careful about what you copy in! Make absolutely sure you copy OUT first, maybe twice then generate checksums and compare to ensure you have a good read.

author: dgimb
author_rank: Newbie
timestamp: August 21, 2024, 04:18:51 pm
content: Quote from: David Hess on August 21, 2024, 03:47:01 pmPin RD*\1 did not receive a signal from another part of the circuit(see screenshot).RD*\1 had about 2.3V and this was an undefined state for trigger.It was resolved with a long wire through the main board

author: dgimb
author_rank: Newbie
timestamp: August 21, 2024, 04:25:47 pm
content: Quote from: TERRA Operative on August 21, 2024, 04:15:42 pmThank you very much for your help!

author: lordium
author_rank: Regular Contributor
timestamp: September 22, 2024, 01:45:52 am
content: I recently just happened to buy one of these TDS820 for some testing. I did a backup of the firmware and nvram (v2.03e) and unlocked the FFT (option 2F). I attach here if anyone needs in the future.Unlock option 2F (FFT):unlock nvram switch on side first, send commands over gpib, then lock, reboot, donePASSWORD PITBULLWORDCONSTANT:ATPUT 327689,1commands I used to get the firmware/nvram:./tektool -r NVRAM_all.bin -b 0x04000000 -l 0x100000./tektool -r firmware.bin -b 0x01000000 -l 0x400000

author: alefeev
author_rank: Newbie
timestamp: August 22, 2025, 02:37:10 pm
content: Hi all many thanks for all post ant this blog !I bought a refurbished TDS820 from a lab, but the device doesn’t boot. Just a black screen and some LEDs lit.After searching on EEVblog, I saw that I need to connect to the debug/console port to check the boot log. Thanks to @maurit, I bought his adapter to make this easier.My boot log goes until the line: Enabling Bus Control Register. Value = 0x67. From other logs posted here, I see that after this line the IMR1 register should appear, but in my case nothing more is printed.I believe the IMR register is the Interrupt Management Register?I have been searching for a full schematic of the TDS820 processor board but couldn’t find it anywhere. If someone has a link, could you please send it by PM? Many thanks!I already checked all the documentation on w140.com Tekwiki and other resources, but found nothing about the schematic part showing the IMR interrupt line and the IC involved.I cleaned the whole board, especially several areas with oxidized pins (seems like condensation damage over time). I think I fixed all visible PCB problems, but nothing has changed: the boot process always stops at the same point.

author: TERRA Operative
author_rank: Super Contributor
timestamp: August 22, 2025, 04:59:29 pm
content: Unfortunately you won't find schematics anywhere. Tektronix only ever reluctantly released schematics for a few TDS500 series scopes due to requirements of government contracts.Depending on the processor board in your scope, the TDS500 series schematicsmightprovide some clues...Can you take a look at the 7-segment display on the processor board and tell us exactly what is displayed if it stops on a number? (A normal boot should have two segments alternately flashing like lights at a train crossing).

author: alefeev
author_rank: Newbie
timestamp: August 23, 2025, 04:29:36 pm
content: Thanks !So yes the Lcd give some number and letter:Ok a little video of the LCD when power on the Tek to see the video is compress in 7z file to be abble to post !The video Show sequence :1: number 8 ..on the video we see the power starting up and show the 7 led become more lighty.2: number 13: little d or transition of the lcd to the next ?4: number 25: number 36: number 9 but i think transition to the 3 next number ? or this is very fast sequence and the cam don't shoot them full.7: number 58: number 69: number 710: letter E and this is the last digit displaying and the Tek is Blocked at this..After i have switch on off 2 time and the sequence is always i think the same..

author: Tantratron
author_rank: Frequent Contributor
timestamp: August 23, 2025, 05:08:16 pm
content: Bonjour, since you have a DOT with a letter, this means always a failure pointing to the small letter.Except in your case, you have .E (big E) which is due to memory problem, PCB trace cut, EEPROM checksum and execution of assembly language of 68020. Somewhere the data is corrupted so at some point, the 68020 does not recognize the instruction => Exception.I had a similar issue .E with a TDS784D and it required lot of investigation including use of logic analyzer.Bonne chance

author: alefeev
author_rank: Newbie
timestamp: August 23, 2025, 07:03:32 pm
content: Bonjour! Someone from France too, nice ! Thanks for the reply.Many thanks for this information about “.E” — I didn’t know the “.” was so important.This will really help me in my investigation now.The boot log shows that all Boot ROM checksums pass, and the bus error timeout test also passes… so the issue is probably in the RAM bus or a RAM chip that has failed!Today I investigated further and found that one “AM29C841ASC” gets very hot… so perhaps this chip has failed. I must to test this first.Hopping the luck will be with me..

author: TERRA Operative
author_rank: Super Contributor
timestamp: August 24, 2025, 08:24:17 am
content: Check some of the TDS500 series service manuals, one of them has a decent description of the errors and memory stuff.This one is about the best we'll get. Most of the processor board stuff will match or at least be very similar:https://w140.com/tekwiki/images/0/07/070-9710-03.pdf

author: madao
author_rank: Frequent Contributor
timestamp: August 25, 2025, 03:22:26 pm
content: Important quesistion:Which data code ?I feel: TDS820/840 share similar issuses with TDS500/500A with smd capacitor plague .DS1245 is using only in old TDS500/600 without suffix.Possible was this a reason for broke pcb trace ...

author: alefeev
author_rank: Newbie
timestamp: August 26, 2025, 04:47:44 pm
content: Ok thanks @TERRA Operative and @madaoThe Tds540 schematics is the same that mine i think !] https://w140.com/tekwiki/images/a/a4/Tektronix_TDS540_Schematics.pdf]So i have a DALLAS DS1245Y-120 ! So i wil read all the post about the ds1245 on the 500/600 series

author: Tantratron
author_rank: Frequent Contributor
timestamp: August 26, 2025, 05:09:32 pm
content: Bonsoir@alefeev, I look at your pictures but did you do some resolution bit change because it seems bit wierd or uneven the change of colors, contrast.Unless I'm wrong but there might be some corrosion on some part of the PCB unless it is a visual artifact (my previous comment).

author: alefeev
author_rank: Newbie
timestamp: August 26, 2025, 05:40:14 pm
content: Yes it is visual artifact because i have scan all the board mm by mm with my microscope to remove and clean all oxyded zone ! I want put a better resolution but the forum limit me to 800ko so i have put to the max i can to put on the forum. perhaps send you the best full resolution i have by mp ?Here i have put a more standard resolution so less details but less compression and give better colors but again very bad than the high size version.

author: Tantratron
author_rank: Frequent Contributor
timestamp: August 27, 2025, 01:35:00 pm
content: From what I see on your last picture, the processor board does not seem so wounded or corroded so the test failure .E must be due to one chip memory because the Kernel boot per your video was able to pass significant test phases. I recommend you check DRAM integrity because if BootROM has valid content, at some point it will transfer the rest of 68020 execution inside DRAM.

author: madao
author_rank: Frequent Contributor
timestamp: August 27, 2025, 06:30:07 pm
content: data code 1992 ... pleas stop with powering and replace all SMD electrolytics (and washing PCBs). if you haven't remove old capacitor.I am sure: if you solder on smd electrolytics, it would smells like railway station toilette (not japanese ! )Not only CPU Board, also frontplate and acqusistion board (be careful with sampling oscilloscope input, it is extremely ESD sensetive)All SMD electrolytics up to 1994/1995 is very often bad..

author: picburner
author_rank: Frequent Contributor
timestamp: August 27, 2025, 06:49:57 pm
content: And if you have the RS-232/IEEE1284 interface (Opt. 13) the electrolytic capacitors need to be replaced there too.