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Sansui AU517 Protection/Tone Control Board Troubleshooting

J

jonah1979

New Member
Hi,
So I'm onto my second AU517 refurb. project. The amp was all original when I bought i, but would not come out of protection. The light would just blink forever. Regretfully, I didn't do much trouble shooting before I dove in for a full electrolytic recap, fusible resistor, VD1212 diode over haul.

Well... It still won't come out of protection unless I bypass the preamp via the switch on the back. At that point, the amp sounds amazing through both channels as it functions perfectly as a power amp.

If I switch the AU517 to "Coupled" via the switch on the bank and turn the amp on, it does not come out of protection. If I remove the 5 pin connector to the Tone Control Board (2673) it comes out of protection. Not even sure what to look for as there doesn't seem to be anything obvious on board 2673 that is off. I recapped and replaced the VD1212 diodes on 2673, but nothing else.

Does anyone out there have any insight as to trouble shooting this?

Thanks in advance,
Jonah
 
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That was fast!

Im not an electrical engineer but Im learning. By the pre amp board, do you mean 2673 (tone control board)? Pardon my ignorance. Might be more help for a beginner if there was a block diagram...

Anyway, Ive gotten it to come out of protection with board 2673 (tone control board) plugged in via the 5 pin connector. All voltages seem fine according to the schematic; however, it still is not behaving. When I turn up the volume a vey clicks the protection relay is tripped. When I turn the volume back down, the relay engages and there is power.

Even with the volume up and the really engaged, it doesn't pass sound. Again, with the preamp completely disengaged it sounds great!

Ughhh
 
jonah1979 said:
That was fast!

Im not an electrical engineer but Im learning. By the pre amp board, do you mean 2673 (tone control board)? Pardon my ignorance. Might be more help for a beginner if there was a block diagram...

Anyway, Ive gotten it to come out of protection with board 2673 (tone control board) plugged in via the 5 pin connector. All voltages seem fine according to the schematic; however, it still is not behaving. When I turn up the volume a vey clicks the protection relay is tripped. When I turn the volume back down, the relay engages and there is power.

Even with the volume up and the really engaged, it doesn't pass sound. Again, with the preamp completely disengaged it sounds great!

Ughhh
Click to expand...

They go to the preamp, but when I say "pre amp out" I'm referring to the pre amp output jacks on the back of the receiver.
I'm talking about connecting between the center pin of the jack and ground, to see if there is any sort of voltage coming from them.
With the volume turned down and the preamp separated from the main, check for any DC or AC voltage, from both the left and right channel preamp.
 
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With the volume down and the preamp separated, I'm getting no voltage (0V) at both the left and right Preamp Output RCAs at the back of the unit.

Moved through the Tone Control Board (2673) and all voltages are good at the test points per the schematic. Hmmmm....
 
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