The tektronix tds 640A oscilloscope does not work after cleaning.  Everyone help - Page 1
Forum section: electronics / repair

author: uoemx
author_rank: Contributor
timestamp: October 16, 2022, 03:03:18 am
content: Hi everyone, I recently bought an old tektronix TDS 640A oscilloscope. At first the machine did not work, I opened the machine and was guided by my brother to put the switch s1002 to the protect position and the machine worked again. Then I opened the Processor/Display board (A11) and the power board cover to brush and blow the dust. After cleaning, I attached all the connections and then booted but the machine did not show up and the led on the Processor/Display board (A11) was still hanging in the top dash. I tried unplugging and re-attaching the connections but the machine didn't work. I read the instruction sheet according to the manufacturer's instructions to turn 8 switches s1001 to the open position and then restart the machine but the machine shows the word .d. I turned the switch to the unprotected position, showing the letter .c as shown in the video. My machine does not have a board below the A11 board. Now what do I have to check? Everyone help me out.I sincerely thank! Video description at here:https://youtu.be/fc0xZWVfkAg

author: manicdoc
author_rank: Unknown
timestamp: October 16, 2022, 06:22:31 am
content: had the machine been recap'ed? - i.e. the capacitors checked for leaks and replaced? This is a common failure mode on old TDS's and is something you should check before powering on for the first time. Check the bottom board, especially for this. The leaking electrolyte out of the caps eats away at the PCB when it's powered up and creates merry hell with the signals. Tracks can short or be eaten away.If there is no sign of leakage, and you have a multimeter handy, grab the schematic and measure rail voltages, +/- 12v, +/- 5v. Also, see if you can grab a service manual for the 600 series TDS.There is also a golden rule to follow unless you know exactly what flicking a switch does - do not switch it... The 8-way dil switch can mean all sorts of things to the start-up sequence and its settings get modified or wiped, especially if protection is turned off.

author: uoemx
author_rank: Contributor
timestamp: October 16, 2022, 07:04:52 am
content: Thanks manicdoc for the reply. I have read the manufacturer's instructions briefly when the machine has a problem. As for the board I have measured briefly in some locations, there are 12.05v and 5.04v sources in some capacitors. All capacitors on board are manufacturer's capacitors I haven't changed one since it didn't start. However, I don't remember turning off the protection switch and then flipping the 8 switches s1001? But since I cleaned and reinstalled, the machine has not booted successfully once. I have repaired a few models of digital oscilloscopes such as tds 2014, tsd 220, tds 210, tds 2012... but with this oscilloscope I just met for the first time so I don't know how to handle it? I have an RT809H programloader to run nvram, but I'm not sure if that's the problem? In the immediate future I will replace the capacitor and back up the dallas ic. Do you have any suggestions to help me?

author: manicdoc
author_rank: Unknown
timestamp: October 16, 2022, 07:59:35 pm
content: The 500 and 600 series can be problematic. Do you get anything on the display, do you see the front panel lights operate, or relays operate?Do you have a serial interface on the scope? you want to see the detailed diagnostics when it starts up.

author: uoemx
author_rank: Contributor
timestamp: October 17, 2022, 01:42:20 am
content: Thanks manicdoc. I'll definitely use the rs232 port to see what's going on inside. From where can you know the cause? From capacitor or from nvram. May I ask if the nvram dies can I replace it with another nvram and backup or replace it with another ic? In Vietnam, this type is a bit rare

author: manicdoc
author_rank: Unknown
timestamp: October 17, 2022, 04:33:25 am
content: There is a Dallas NVRAM replacement that is a subboard with detachable batteries - you can get it on eBay.https://www.ebay.com.au/itm/293932968205double check that is what you need.If you look at the tekforum andhttps://w140.com/tekwiki/wiki/Main_Pageand on here you should be able to find images. If you have a GPIB adaptor you can read/write the NVRAM remotely, ideally, you should dump the NVRAM before removal, as removal will often kill it.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 17, 2022, 11:00:19 am
content: Make sure the vertical PCB connector board located on the right side of the scope that connects the top processor PCB to the lower Acquisition PCB isn't installed upside down.It will plug right in either way around, but machine won't boot if it's upside down.The correct way is indicated by the acquisition PCB end being labeled as such, so the end with the unpopulated connector footprint is towards the top (It will be populated with a connector if the TV Trigger option is fitted).Almost all of my scopes have the s1001 switches all off. It bypasses some self checks for faster boot IIRC.Your error code of .d means the boot had halted on an error (the . ) with a problem with 'FlashROM Dsacks'My thoughts would be to suspect the NVRAM's and capacitors first, after checking and reseating all connections.Here's a link to the error codes for these units:https://www.eevblog.com/forum/repair/tds744a-hangs-with-7-segment-code-l-or-segment-f/msg4417540/#msg4417540Copying the NVRAM can be done with a floppy disk using a utility on these forums somewhere, or via GPIB with a small DOS application which is also on this forum (that does even run in Win10, it's how I do it), but with a non-booting machine will probably require removing the Dallas chips from the PCB and sticking them into a chip reader.Imighthave NVRAM images to suit a 640A, but not sure... most of my units have been the later revisions. I'll have to check when I get home.If you get the scope working, and can copy out the firmware and NVRAM, I'd appreciate if you could send me a copy for the collection.As for capacitor replacements, it's not a particularly difficult job if you have a fine tipped soldering iron, just a little time consuming.I recommend putting the PCB's through the dishwasher after removing the old capacitors (and noting the capacitance and voltage rating for each one to make sure you install the correct replacements!), or at the least giving them a good clean with dishwashing soap with a soft brush and a good rinse in clean water afterwards followed by a blow out with compressed air and a while in the sun to dry off.A bit of isopropyl alcohol to clean any residual stuff if any caps had leaked will then let you see of any repairs are needed.

author: uoemx
author_rank: Contributor
timestamp: October 17, 2022, 05:11:12 pm
content: Thank for all. I will try every way everyone suggested

author: uoemx
author_rank: Contributor
timestamp: December 13, 2022, 04:23:36 pm
content: Hi everyone, I'm back with disastrous results.1. I cleaned the A11 board and replaced all the capacitors on the board2. Follow the instructions on the manual server, the result is that the A11 board must be replaced (pressure measurement, frequency measurement in some places on the A11 board...)3. My oscilloscope seems to have lost nvram on 2 ic ds1486 and ds1250y. So I have to reload the program for these 2 ic with a xeltek charger that I have to pay for the service. Because charging with GPIB cable in Vietnam is very expensiveNow, I don't have files for ds1486 and ds1250y. I hope everyone can back it up and send it to me, I'll be very grateful

author: uoemx
author_rank: Contributor
timestamp: December 15, 2022, 01:19:52 pm
content: I shaved the DS1486 memory ic with 2 batteries and the DS1250Y memory ic both have enough 3v. I have a program loader TL866-3G and RT809H. Now I don't have files for ds1486 and ds1250y. I hope everyone can back it up and send it to me, I'll be very gratefulI thank you once again

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 15, 2022, 02:25:11 pm
content: I don't have the firmware file, but I have this NVSRAM file, which would probably be ok to use for the DS1250 chip.

author: uoemx
author_rank: Contributor
timestamp: December 16, 2022, 01:15:10 pm
content: Thanks TERRA Operative. If you have the file of ic ds1486, please give it to me

author: uoemx
author_rank: Contributor
timestamp: December 18, 2022, 03:50:45 am
content: i have reloaded nvram ds1250y with tl866-3g loader but the result is still showing .d. So I need the flashrom file of ds1486, who has the file of Tds640A and ds1486 please let me know

author: uoemx
author_rank: Contributor
timestamp: December 21, 2022, 11:31:01 am
content: My backup Tektronix TDS640A. I need ds1486 flash ic file. Please send it to me!

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 21, 2022, 11:41:41 am
content: Unfortunately I haven't had a TDS640A on my bench, so I don't have any files beyond the one I already provided.Youmightget more luck if you ask on the Tektronix or Tektronix2 groups.io pages.