hifi engine

Pioneer QX-747

Hello all i am new here. I own 2 Marantz recievers. A 2270 and 4240. I have good basic understanding of how electronics work. I am an autotech. But mostly we deal with only DC circuits. I bought this Pioneer for cheap and it powers up and can here noise through the head phones. All the fuses test good. The protection relay clicks when powered up although sometimes it takes a while. I have no audio output. I have a nice fluke meter to test with and i am looking to get some help on where to start.


Pioneer QX-747

This I believe is the 4 channel unit with the "Radar scope" in front on the left.

Because this is a Quad capable of doubling the power for stereo, it has a special plug in the back to switch from 2 channel to 4 channel. If the plug is missing, or the thumb screw isn't tight, you will not get any speaker output, (Although I think this would kill headphones as well.)
You could have a dirty speaker protect relay. Tap it with the plastic handle of a small screwdriver to see if sound comes on and off.
Switches and controls on this unit will also kill all sound if dirty, especially the 4 channel, tape monitor, and mode switches. tap them in and out to see if you get anything. I will warn you that this unit is very difficult to disassemble the necessary things to properly clean and lube all controls and switches. You will need to get some Deoxit D100 and use the long and thin nozzle.