Electronics > Repair

Fluke 8506A , need help with repair

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bdunham7:
So I poked at my spare panel board.  The three displays don't share a high-side driver, but they are all multiplexed through the 'J' circuit of U30, U25 and U20.  I tested using pin 12 of U20 for my low side and the collectors of Q2-Q8 in turn.  If the problem is in the 'J' circuit, you should also see the REMOTE (pin 19 U26), HI ACCURACY and NORMAL (pins 2 and 4 of U14) fail to operate.  Hopefully you have a clear schematic you can see all of that on.

m k:
I had once a problem where certain number turned on segments elsewhere, error segments were bright.
Reason was too high 5V, finally everything went blank and 5V was 7V, or something like that.

GigaJoe:
Thanks bdunham !!!

correct U 34 , 24, 13
and exact the thing -  AC: HI ACC, NORMAL - not lit up  (remote -not up, getting err-4)

I attached stitched schematic for the front board , will dig now ....

had replace all caps on PSU and adjust it ... but will check again

GigaJoe:
finally ...

i fix everything , clean everything ,  assemble everything ...   a small job need on ohm board .. but so far all great

shorted\soldered  front-back switch no  need it
add a lot SMD caps on digital part of ADC , and a lot additional caps on power analog ADC parts ;  same for digital isolator board.
as well replace electrolytic caps on boards,     for some i wasn't sure and left it ...

seems all in a normal order,
at first - noise about 0.3 microvolts , and cold-hot drift about -4ppm ;  I think it good numbers 
plans to leave it to for a month or more in "ON" state then do adjustment

maybe ... as an option to do something with Vref ...  make it better a bit. or... more likely use embedded option to switch to Ext ref.

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