Get a Tektronix TDS540 working again (again :-) ) - Page 1
Forum section: electronics / repair

author: Oldy_5volt_guy
author_rank: Newbie
timestamp: March 27, 2025, 07:16:34 pm
content: Hi!New to the forum, but it seems this forum have a lot of very very knowledge members!Short, my issue is I a couple of years ago made the tedious work of replacing all darned leaky capacitors on a TDS540 oscilloscope, cleaned it in IPA three or four times and got it to work on channel 2,3,4 channel 1 had some issue with a capture memory, but I was happy I got it to work at all and three is better than none.Needed to use it a year ago and it was dead, only lit the led up but never the screen. I have done thoroughly testing and run all diagnostic tests, and it fails only on the dreaded test "NVRAM Ram DSACKS" so the Dallas 1645Y was corrupted. I made a surgery of the thing replacing the battery with a 2032 holder and succeded in the operation, with some bloodshed offered to the gods of electronics since there are some really nasty sharp parts when removing the old battery.Since then I have tried to get it to work again, I bought a National Instruments AT-GPIB/TNT card, gone through my stash of old PC to find one with ISA ports, installed both Debian and Windows 98 to get that card to work. All since I found there are some tools to download/upload images to the NVRAM, but it seems they all require an at least booting system into screen to function. There is a mysterious "Enter SDM Monitor via the GPIB" settings, and I can detect within National Instruments GPIB tool, that the scope is found at ID 29. However I'm not able to utilize it in any way, and searching this term SDM mode on Internet to understand what it is used for gives nothing.My second attempt was to use a newly invested in T48 programmer to download a new NVRAM image from the only repository I found on internet (TDS540_v2.16e_Firmware.zip) to at least get the scope to boot. I know the firmware in the flash probably must match the version in the NVRAM, and of course it epically fails! But I can see that after removal of the NVRAM some of the first bytes in the addresses of the chip are changed so some execution of code is done.The modified Dallas 1645Y chip is working and a verify check says it is OK, so that part works.What I'm curious about is if I need to offset before writing that .BIN file to the chip?Also are there a way when this scope is in the state as it is to "upgrade" the firmware on the flash memory to play nice with the NVRAM image (from the v2.16e package)?I don't know what version I actually have, I can see on the label that the EPROM is version 1.5. something (the label seems to short to show the full version). The scope is manufactured in 1993 or a bit later since 93 is stamped on lot of the chips.Any help is appreciated since I think this is a horrible waste of a marvelous Tektronix equipment to just dump it.

author: TERRA Operative
author_rank: Super Contributor
timestamp: April 07, 2025, 04:49:03 am
content: Does ypur scope have one or two NVRAM chips? What are their part numbers?The changing values are probably the real time clock ticking away.If you are able to get a programmer to read the chip, be careful to verify that the first couple hundred bytes are copied correctly, the T48 has a habit of starting to read before the chip is ready to be read..Does ypur scope have a circuit board plugged in behind the front control panel?I remember some 500 series scopes do, but I never remember what exact model numbers they are.If it does, this is the 'firmface' board that holds the firmware.Also, you may find that your scope holds the calibration constants in the NVRAM, which will meen recalibrating the scope if they are lost. But you have the National Instruments GPIB card, so you have the hard part done (besides getting the required calibration equipment...)On that note, you don't need the NI GPIB card for talking to the scope, or copying NVFAM and firmware in and out. You can do it under windows with any GPIB adapter, even USB.There are instructions around on this forum somewhere with the software to use. (I just updated the firmware in a TDS784D on the weekend in Win10 with a Keysight USB-GPIB adapter).Actually, double check the memory protection switch is set to protect (it's on the front right of the top processor board) or the scope won't boot. The switch should be switched towards the back of the scope.If the case is installed, you will see two small holes in the case on the right side where you can poke a thin screwdriver in the rear of the two holes to carefully switch it.Also, make sure the interconnect PCB on the right rear of the scope that connects the top processor board and lower acquisition board is installed correctly. If it is upside down, the scope won't boot. No damage will be done but just no boot.

author: Oldy_5volt_guy
author_rank: Newbie
timestamp: April 25, 2025, 12:30:43 pm
content: Hi!Thanks for replay!Does ypur scope have one or two NVRAM chips? What are their part numbers?Only one this is a TDS540 basic, using Dallas DS1645Y-120 (Has no RTC, I think only 6xx and later series had it?)The changing values are probably the real time clock ticking away.To my knowledge this version has no RTC on board and neither on the Dallas chip.Does your scope have a circuit board plugged in behind the front control panel?Yupp, Was a bit confused first time I had to repair the scope and found this card full of SMD flash chips, if I recall correctly 28F010 sized.Also, you may find that your scope holds the calibration constants in the NVRAM, which will meen recalibrating the scope if they are lost.Yes. that's the hard part, the NVSRAM is/was corrupted after a year without use, since last time the battery had probably lost the last juice to keep memory.On that note, you don't need the NI GPIB card for talking to the scope, or copying NVFAM and firmware in and out. You can do it under windows with any GPIB adapter, even USB.There are instructions around on this forum somewhere with the software to use. (I just updated the firmware in a TDS784D on the weekend in Win10 with a Keysight USB-GPIB adapter).My issue is that the GPIB interface not even discover the oscilloscope, at some point I got response from 29 (I think it was) but could not talk with it properly, the normal address should be 1 if it is not changed. But since I not even can get the scope to boot I can not change the GPIB address.Actually, double check the memory protection switch is set to protect (it's on the front right of the top processor board) or the scope won't boot. The switch should be switched towards the back of the scope.If the case is installed, you will see two small holes in the case on the right side where you can poke a thin screwdriver in the rear of the two holes to carefully switch it.Yes, I tested both settings. None or minimal difference between the to modes what I could see.Also, make sure the interconnect PCB on the right rear of the scope that connects the top processor board and lower acquisition board is installed correctly. If it is upside down, the scope won't boot. No damage will be done but just no boot.Thanks! I got up my hopes there for a moment but the interconnect card is put in right direction, I have three slots on the top matching the possibility for two extra cards around the processor board.