Electronics > Repair

Tek2440 Mini teardown, NVRAM replacement and calibration

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LazyJack:
What do you mean by "bricked"? Does it not power on, or does it not pass the self test?

bob91343:
Neither.  It comes on and the display is nonsense, unaffected by any controls.

LazyJack:
Try reseating and checking all the connectors. Look at the ribbon cable connectors on an between the two large foldout boards and also the side board. I assume you have removed these when replaced the nvram. I once had a similar experience, one of the connectors were not properly in place and got a garbled display.
Also check the power supply, the PSU in the 2440 is known to have problems with caps leaking or drying out. I'm not a fan of recapping for just the sake of it, but in this case it may be legitimate. Check the powers for value and riplle on the side board test points. Although if it was good just before the nvram replacement it would take a huge coincidence of just going bad now, but it is not impossible.
I also assume that the replacement nvram came from a reputable source and not some aliexpress fake chip. Hopefully you used sockets, so you can try putting in the old ones, the scope should start and ask for a calibration even if they are discharged.

bob91343:
I do suspect counterfeit chips.  That's why I tried putting the old ones back but one of them got damaged and I didn't take care to see which was which.

Power supply is okay.  Connectors have been reseated several times, although I don't think the GPIB line makes any difference since it just goes to an outbound connector.

LazyJack:
You could try and use a programmer to read the chips and see if they are ok. The TL688 programmer reads them, I ve tried it. Or just connect it to an arduino.
Or you could even make an adapter to use some normal sram chips instead, just to try if the scope starts up.
Other than that, I would also suspect fake chips.
If you have only one good old chip, you could use it in place of U664, that is the system ram, the other is the waveform save ram. You would probably get some startup error, maybe it would not even get to the point of producing a display, but it should flash the startup error code on the trigger leds. BTW if you remove bot nvram chips, do you get any acivity on the trigger leds? A fake chip could disable the cpu completely, but a missing one should at least enable it to start the basic tests.

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