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Sansui AU-919 Ground problem? Advice needed

J

Johnev35

New Member
I am restoring an AU-919 and found that I am not able to zero the output of the F2846 Tone board. One channel can be zeroed but the other channel starts with mV of offset then slowly climbs to +20V and the adjustment pot has no effect. The board has been recapped, the 2sc1313 transistors and the zeners were all replaced. I checked all the components, including resistors. I think this is a grounding problem since the output slowly drifts up in value. I cannot get continuity from the F2846 ground traces to chassis ground. Looking at the schematic, the ground path seems to go through several boards and ends up at the driver board, which is then connected to chassis ground. Any advice on what else to check or guidance on the grounding scheme would be much appreciated.
 
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No schematic handy right now but in your shoes I'd chase that gnd issue back from the chassis connection. Lots of weird problems can result from missing out intermittent ground connections.
 
jmjrcy - good advice! Will start there. For other readers, the board in question is the F2841, which is attached to the F2846.
 
Problem solved! The short answer is pilot error. I did not have the input cables to the driver board plugged in. I mapped out the grounding scheme and saw that the ground for F2841 goes through F2838 (Pre-out/main in) to the driver then to chassis ground. Thanks for the help!
 
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