Yamaha R-8 Power supply transformer or bridge rectifier problem?

[rocknroller]

Have this amp with audio going into the power amp section, no fuses blown but no output either, and bad (low) rail voltage of like -2/2v coming off the Bridge rectifier D5FB20. Can't find an actual R-8 schematic but this is a R-9 and should be almost identical. Got about 33vac across the BE terminals from the transformer but 91vac across the Reds, where schematic says should be 61.7vac. Is the rectifier bad given it's only putting out 2vdc? Blown because the 91vac input? Both the transformer and Rectifier bad? Transformer just showing wrong readings because rectifier is bad?

 

[avionic]

Pull the bridged rectifier from the board and test it like 4 individual diodes.

 

[avionic]

Transformer just showing wrong readings because rectifier is bad?

What is the part number printed on your R8 transformer? GAxxxx?

 

[rocknroller]

Pull the bridged rectifier from the board and test it like 4 individual diodes.

Thanks for the tip. Turned out not to be the rectifier at all. When I opened the bottom of the case to get to it to desolder, I could see the main board had a SEVERE crack though it. Couldn't see this from the top side as the wiring obscured it. Yahama used rubber "bumpers" between the bottom of the case and the board, at the middle of the board where it is the weakest. Someone must has dropped this at some point, pushing the board upwards with some severe force, though there's no external sign of that. In any case, it cracks right through the traces at the rectifier.
Ran some heavy gauge wire from the 3 cutoff points and all is well. Runs great!

 

[rocknroller]

What is the part number printed on your R8 transformer? GAxxxx?

Probably irrelevant now but ga6911

 

[avionic]

Thanks for the tip. Turned out not to be the rectifier at all. When I opened the bottom of the case to get to it to desolder, I could see the main board had a SEVERE crack though it. Couldn't see this from the top side as the wiring obscured it. Yahama used rubber "bumpers" between the bottom of the case and the board, at the middle of the board where it is the weakest. Someone must has dropped this at some point, pushing the board upwards with some severe force, though there's no external sign of that. In any case, it cracks right through the traces at the rectifier.
Ran some heavy gauge wire from the 3 cutoff points and all is well. Runs great!

Outstanding..