Electronics > Repair
Tektronix TDS 694C not booting
TERRA Operative:
The cal data is stored in an EEPROM on the acquisition board, so it should be pretty safe.
If you need chassis parts, I have a few spare bits, pending postage costs from Japan... Might be able to get in under the limit for 'small packet' if we are lucky to get cheapest rates.
I think replacing NVRAM with new is a good next step, as long as you can get a good firmware and NVRAM image from another scope you should be golden. The batteries in the chips are weellll past their use-by date....
There are many shared parts, so your test on swapping boards is valid.
I have loaded different firmware into a board and was sucessful in changing it to suit the new scope it was going into. If the part numbers match, it's good to go.
cf4044:
--- Quote from: TERRA Operative on January 17, 2024, 11:22:29 pm ---....
I think replacing NVRAM with new is a good next step, as long as you can get a good firmware and NVRAM image from another scope you should be golden. The batteries in the chips are weellll past their use-by date....
......
--- End quote ---
I just ordered the NVRAMs as you suggested from kellyjo_13 on eBay. Actually I ordered two sets, one for the TDS694C and another for my (still working) TDS 784C as the batteries on that will definitely run down some time soon.
The NVRAMs will be pre-programmed with the appropriate data for each model, so if nothing else is wrong I'm hoping it's just a matter of putting them in and switching on.
It looks like they will take a while to arrive though, the estimated delivery being 27th February :-(
In the meantime I will prepare by desoldering the NVRAMs of the 694C, which I am not expecting to be particularly easy.
--- Quote from: TERRA Operative on January 17, 2024, 11:22:29 pm ---....
If you do manage to find firmware etc, send it to me and I'll upload it here:
https://w140.com/tekwiki/wiki/TDS694C
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--- End quote ---
Sure, if I manage to get it to work I'll be glad to send you the firmware, but I'll probably need your help on how to download the firmware from the scope.
cf4044:
IT'S ALIVE !!
It was actually the NVRAMs - thanks for the advice in that regard.
That was probably the last thing I would have thought of. I would have thought that it would go through the boot, come up with some message that it is loading with default values or something like that and then proceed to work, possibly with limited capability and performance. It's kind of weird that it's designed to instead just stop with a blank screen not letting you know what is going on.
I just received the replacement chips/modules yesterday, installed them and it worked just right away, even passing all the self tests and successfully doing the signal path compensation.
Unfortunately I confirmed the triggers are not working though, not entirely unexpected given that one of the trigger chips is literally burnt through. There seems to be some limited triggering ability - I could get it to trigger through the Ext trig and the Logic triggers but very unreliably and only work at relatively low frequencies.
In any case in an effort to prevent the triggering system from deteriorating further I jury rigged a heatsink for the three remaining chips. Even so the heatsink still gets very hot so I can only imagine how hot the chips were getting with no heatsink at all.
I had considered swapping around one of the chips as it seems that fixes the trigger problem, probably at the cost of the currently working (sort of) logic trigger. That would be fine but at this point I'd rather not risk making it worse by a bodged repair as I'm not very skilled at SMD repairs.
I have attached some photos of the heatsink addition. The main challenge was how to secure the heasink in place. I didn't want to glue it as it would make it next to impossible to remove the chips intact if I eventually decide to swap them around. So the only way I could figure out to secure it was to use a longish brass bar to span the nearest two screws that mount the PCB to the chassis.
darin_i:
I like your heatsink mounting method. Sort of reminds me of the spring clip heat spreader retainers in GPUs, etc.
Only way beefier. Did you work from a drawing of some kind you can share, or just wing it with show tools?
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