TDS 620A Acquisition failure

[mwbarth36]

A common problem with the TDS620A Tektronix scope is that it will pass all startup test except Acquisition and/or Acquisition Interface.  Yes, I know about the leaky electrolytics, and replace all before even trying the scope.  However, replacing the capacitors rarely, if ever, solves the Acquisition Fail problem.  Have tried to insure there are no broken traces as a result of the leaking capacitors, but the job would be infinitely easier if there were a schematic diagram available for the Acquisition board.  First, does anyone know if there is any hope of obtaining a schematic for this board?  I have heard the TDS520B might be similar, but looking at the board layout, it is not obvious.  Any help will be GREATLY appreciated!

[madao]

 Have you washed  PCB after removing of bad capacitor?
Only replacing of eletrolytics doesn't run good.
Than,  pleas run  SPC, if it fails , tries again (2-3x try)

TDS640A Schematic  exitist. But  it is not exact same, but  nearly to TDS620A
http://hakanh.com/dl/docs/hardtofind/TDS644A_A10(Acq).pdf


I have a wish: Pleas  shot a pic of your  TDS620A Acquisition board, good quality. I want seeing him and added it to tekwiki (w140.com)

regards
Matt

[nctnico]

You don't need the schematics. Just make sure to wash the board with alcohol and then Simple-green / St Marc. If there are still problems then resolder joints which have corrosion on them. From what I've seen one failure during boot is not so bad and replacing the capacitors + washing the board should do it. From what I've been told the board should never be washed using an ultra-sonic washer.

[shakalnokturn]

https://www.eevblog.com/forum/repair/tds-620-still-failing-after-recap/msg1605454/#msg1605454

Just cross-linking... I haven't got any further on mine since.

Would be interested in some voltages / waveforms on a working scope's FISO for reference.

[mwbarth36]

Will try to get a good photo of the acquisition board and send it.  May take a few days.  I have washed the board and checked the lands and feed thru's.  Could have missed some, for sure, but feel there is another problem with this board.  The schematics you reference are close, for sure, and will help a lot.  Thanks again.

[george.r]

Check the flat cables going between A10 and A11. They are finicky and may cause ACQ to fail. Also the weird busboard right to the side of them, try reseating that a few times.