I am working on an SX-1980 Monster, and I am waiting for the service manual, but was wondering if anyone had a diagram of the power supply that they could email to me. I would like to get started on the repair and believe that the power supply is the problem (I have voltages in the 2 volt range) which for vintage equipment is way out of range. All fuses are good and the rail voltages are good (+/- 91 volts) but some of the other voltages I believe are way off. Nothing functions on the receiver except for the dial lamps. The selector lights do not work and the tuner does not work, there is not output. Since it is not blowing fuses I suspect the none of the outputs are shorted (but may be open).

Any information will be appreciated.

This one?

http://img255.imageshack.us/img255/9673/1980ps1of.th.jpg (http://img255.imageshack.us/my.php?image=1980ps1of.jpg)

Glenn, what do you think about the pair of 2SK34 FETs used by Pioneer on this model? They are not used on the SX-1280 IIRC. I wonder what's the advantage...

The FET's are used as a current source. A bit unusual, and I'm not entirely sure of it's advantages when used at the front end of a regulator like this. I believe it is an attempt to stablize the current through D212 and D213 to minimise changes in the reference voltage provided by the diode.

This one?

http://img255.imageshack.us/img255/9673/1980ps1of.th.jpg (http://img255.imageshack.us/my.php?image=1980ps1of.jpg)

Thanks Glenn, I have not had a chance to see what is wrong but will take a look tomorrow. I see no voltages of 2 volts, That's the first challange.