Troubleshooting Sherwood RV-6010R surround reciever PSU

[AMelbye]

Hey,

I've been having some issues with my sherwood RV-6010R. The unit powers up and parts of the amp are still working. The most significant problem is that the main power amp has died.

I started by checking voltages. My main concern is that there is a significant amount of AC on the B+ line (106 VAc!), which supplies the big power transistors with power. Is this normal?

I have measured the filter caps for ESR, and they're fine. I don't have a way to measure capitance though, is this neccessary?

Have a look at the attached schematic and the picture of the psu board (the filter caps are located at the motherboard btw)


This amp does not have a ground connection, but gets its ground point from a center tap in the transformer. I measured for any differences between chassis ground and the ground in my flat, and they're the same, at least one thing is working like it should


capacitors C606 and C607 are missing, is this a cost cutting measure, or is it so because I have the 230V eurpoean version, and the schematic is for the 110V US version?

I tried also removing C614 and C613, and lifted the "output" legs on the positive half of the bridge rectifier.

On the negative half I get 35VAC in on each input and 0VAC out and -32VDC out, like I'd expect.

on the positive diodes I get 35VAC both before and after the diode (when only one leg in circuit) along with +16V at the output. If I turn the diode around, I get 0VAC, and the expected -16V.

Why does the diode let through AC in one direction and not the other direction? Is this normal? I thought diodes were meant to allow current in only one direction?

Is normal to have a significant amount of AC on one output of a rectifier bridge? I get this without the filter caps attached, but only on one side of the rectifier. Connecting to the mainboard with the filter caps only makes it worse, since there is voltage there too, and they add together. I'm finding this very strange.

Hope you can help
best regards
Audun

I had to upload my "attachments" elsewhere due to file size limitations:
http://www.audunmelbye.no/wp-content...sconnected.jpg

http://www.audunmelbye.no/wp-content...erwood-PSU.gif