Dahond
New Member
Hi,
I'm from Belgium. I've been reading through this forum for a while trying to revive my sansui AU-517.
I've already found some great tips here but now it seems I'm stuck.
The amp was given to me a few years ago, including a sansui turntable and sansui speakers.
I worked great for a few weeks when one day, playing a record, it started smoking and wouldn't come out of protection.
2 weeks ago I've finally had some time to start repairing it.
It was a shorted diode on the powerboard and blown fuses in the left channel.
Fixed that easily, started it back up but it wouldn't come out of protection...
Long story short:
I'm not a technician, I just took the schematic and started measuring and shorted an output transistor doing that :-/
I've changed the output and driver transistors, did a recap of the of the driverboards and the powerboard.
Changed all transistors in the protection circuit, including TR09 on the driver board. Changed out some shorted resistors.
Every component I now measure seems to be within specs.
So here's the problem:
If I use headphones (64 Ohm) it works and sounds great although sometimes at low volume a channel turns scratchy and lowers in volume. Most of the time the right channel, sometimes the left. This can be fixed by turning up the volume one step and then I can lower it again, sounding great again.
If I use speakers (8 Ohm) it immediately clicks back in protection mode. I've tested different speakers.
If I disable the protection circuit it sounds great with my speakers although sometimes the scratchy lower volume random channel thing happens too with speakers but it is fixed with the volume one step up and back down again.
It is also fixed by simply touching the signal coming from the driver board to the protection relay with the probe of my multimeter.
If I listen to the preamp on the preamp out on the back it sounds great, no scratching or lower volumes.
I've read some stuff about the fuse resistors and the diode VD1212 but I didn't replace them because they measured ok.
Could they start misbehaving under load?
I don't know where to go from here. I'm starting to think I should just disable the protection circuit.
Guess I'm looking for some direction on what to check/measure/...
Any help would be very much appreciated. I quite love this amp.
EDIT:
Bias = +-20mV left and right
DC offset = +-1mV left and right
I'm from Belgium. I've been reading through this forum for a while trying to revive my sansui AU-517.
I've already found some great tips here but now it seems I'm stuck.
The amp was given to me a few years ago, including a sansui turntable and sansui speakers.
I worked great for a few weeks when one day, playing a record, it started smoking and wouldn't come out of protection.
2 weeks ago I've finally had some time to start repairing it.
It was a shorted diode on the powerboard and blown fuses in the left channel.
Fixed that easily, started it back up but it wouldn't come out of protection...
Long story short:
I'm not a technician, I just took the schematic and started measuring and shorted an output transistor doing that :-/
I've changed the output and driver transistors, did a recap of the of the driverboards and the powerboard.
Changed all transistors in the protection circuit, including TR09 on the driver board. Changed out some shorted resistors.
Every component I now measure seems to be within specs.
So here's the problem:
If I use headphones (64 Ohm) it works and sounds great although sometimes at low volume a channel turns scratchy and lowers in volume. Most of the time the right channel, sometimes the left. This can be fixed by turning up the volume one step and then I can lower it again, sounding great again.
If I use speakers (8 Ohm) it immediately clicks back in protection mode. I've tested different speakers.
If I disable the protection circuit it sounds great with my speakers although sometimes the scratchy lower volume random channel thing happens too with speakers but it is fixed with the volume one step up and back down again.
It is also fixed by simply touching the signal coming from the driver board to the protection relay with the probe of my multimeter.
If I listen to the preamp on the preamp out on the back it sounds great, no scratching or lower volumes.
I've read some stuff about the fuse resistors and the diode VD1212 but I didn't replace them because they measured ok.
Could they start misbehaving under load?
I don't know where to go from here. I'm starting to think I should just disable the protection circuit.
Guess I'm looking for some direction on what to check/measure/...
Any help would be very much appreciated. I quite love this amp.
EDIT:
Bias = +-20mV left and right
DC offset = +-1mV left and right
Last edited: