Rob357
New Member
I picked up a broken Pioneer SA-7500II for $75. Knowing it has issues, all the fuses were removed. So I decided to save it, came home and replaced the fuses and put it on the dim bulb tester. It lit up like a Christmas tree. After unsoldering the outputs I tested them on the DCA75, one channel had shorted leads. It has smoked the 150 ohm and .5 ohm resisters. I replaced them all with the njw0302G and the njw0281G. It passed the test and sounded OK. So I went ahead with a recap and small transistor overhaul. It does have a channel with over 70mv so I checked the voltage at the outputs. Collectors about + and - 38.5 volts. The I read the bases, way low at + and - .6 volts. The emitters are way low at .05 volts. I have poured over the schematic looking for my missing 1.2 volts thinking without that I cannot get good voltage at the emitters. I have 1.2v at the base of Q11 and Q12. -1.17v at Q9 and Q10. Where did my 1.2 volts go? Or is the emitter voltage my issue? Or both? I am at the limit of my knowledge in circuits. I could have been advised wrong on replacement transistors as well. I will take readings wherever I need to and will pull and check whatever parts necessary. I have been frustrated by this unit but I know this is the learning experience I need. One bright note is that the outputs fit pretty well in the heatsink. I used a 3mmx10mm long button head screw to secure them and turned the mica 90 degrees. A set of long medical forceps was used to hold the tiny nuts for tightening. Also found a drop in replacement for the main filter caps, more on that later. Thank you,
Rob
Rob
