Electronics > Repair

Tektronix TDS7104 repair issue, motherboard

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acbern:
months ago i bought a non-working tek td7104. it was reported to not pwoer on with the front switch, but power on with the internal jumper. it was sitting there for a while because I had no time left to work on it, but have now, so here I am.
first find is, true, with the jumper shorted (it is decribed in the service manual, which does unfortunatelly not go in much detail about anything), it powers up, but thats all. screen blank. I deactivate the ppc board and video (by two jumpers) and i measure all voltages, they are ok, also 5vstdby (so my initial assumption that the psu has an issue seems wrong).
so its now only the nlx baord that should be active, all others being deactivated. so i measure, and issue is, the pci bus reset coming from the nlx board is active, so the board is in reset. this board is an intel su810 nlx mainboard, essentially (as i understand, not being a motherboard guru at all) an at-motherboard design in another form factor, based on the 810 chipset. I measure other input signals (pw_ok, soft_on/off), they are correct.
since i could not find any schematic of this board to trace the reset issue, i am stuck. replacing the nlx board would be the next thing, but that will cost me 100 euro, and may not be the right thing at all, just a guess.
so if anybody has some hints, would be nice. thinking arround measurements on board the nlx or on the pci connector to determine the root cause of the reset, to determine if a new nlx board is the right thing.
so that means any background re. how the restet is generated (when does a reset occure, what signals need to be present on the pci bus), what chip is generating it? and so on.
any other hints wellcome as well of course.

mongo747:
I have a TLA 622 with same motherboard and similar problem.  I have found what I think is that motherboard for about $20 us.
I got it at an auction and it turned on and was able to get past the log in.  It sat for a month or so and now it does power on.

Trying to figure out how to isolate it.  I would like to get in touch and see if we can work through our issue together.  Please send me a message if you would like to give it a shot.  Thanks

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