I hope this post is in the right place? 😕I'm trying to fix a Yamaha RX550 receiver that's about 20 odd years old,the micro-controller seems to be all mixed up with the wrong voltages on the wrong pins it has the right Vcc 5.0v on pin 1 and the 8 MHz 3 pin resonator measures 7.98MHZ ,I cant find anything wrong with any of the transistors,resistors,capacitors except for the big 68000uf power filter rectifier caps,they measure 61000uf & 57000uf respectively,would that be low enough to effect anything?I'm getting a pulse to the micro to turn the amplifier on but the pin that goes to the power relay from the micro that is supposed to have 4.6v has only 0.58v?I can only turn the amp on by using the 3v from my DMM on the transistor driver for the power relay. If anyone has any suggestions or ideas on what I can do here I would really appreciate it.
I take it you have already checked DC offset on the power amps? A service manual may give some more hints, too.
The DC offset is Right,10.1mv & Left,5.6mv,I should have mentioned that all the relays work but only after I hot-wire the amp to start up initially,then the micro wont work to change functions, power on, phono,cd,aux,ect... I have the service manual with schematics the voltages look to be OK except for the micro but I have never had to deal with a micro-controller problem before. I contacted Yamaha for another micro-controller but they don't have them.It looks like I could get one from fleabay but how would I go about programming it?I am determined to get this amplifier going as long as its economical.
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