Help with Pioneer Audio Receiver please...

[sirmikeylikesit]

I posted this a while ago, and didn't get any replies to it, so here goes again!

Hi there folks. My name is Mike and I have recently purchased a Pioneer SX-205 Stereo Receiver that does not power on. I give it 120VAC and press the power button, and nothing happens. I have checked the fuses, and they are good. I get 70-80VAC output from the transformer. I'm not sure what component/s would be bad in order for this unit to not do anything? The only thing that happens when I press the power button is that I can hear a very faint high pitched tone from the main PCB. Very, very faint. Other than that, my desktop light dims a little from applying the load, but nothing else happens... I'm not sure what the transformer is supposed to supply on the output side, but it appears to be good. Any help would be greatly appreciated. I am somewhat new to electronics and am eager to learn all that I can!! Thanks for your time.

UPDATE: I did some more investigating on the main PCB and noticed three small diodes where underneath them the PCB was discolored as if it had been burnt. I removed these three diodes, labeled "A28" or "82A" and tested them, they show an ohm reading in one direction, but not the other, which I'm thinking means they are good? I also removed the small electrolytic capacitor and tested it, and it appears to be good... I'm not sure what these three diodes are used for, and I'm not sure if the PCB being burnt under them is a sign of anything but heat, but I thought I would add it here!

I'm still thoroughly confused by this receiver, and still cannot get it to power up. I get several different DC volt readings across the PCB in different areas... So I'm thinking that the rectifier is good?

I'm looking forward to anyone's input on this matter, It will be greatly appreciated!!

Thanks.

 

[CalebG]

maybe one of the transistors has failed? also one of the circled diodes appears to be reversed from the other 2, Im not sure if it was like that before you removed and resoldered?

 

[unclejed613]

pioneer receivers can be turned on 3 times with an output stage error (excessive output current, DC offset at the speakers, missing or out of spec power supply voltage), and then the microprocessor locks out the power switch. after that, the receiver requires a reset code to turn the amp back on for troubleshooting. the reset codes are found in the service manual, and are usually different for each model. you want to check the output transistors first, not the small diodes (once you find which channel is blown, then begin checking small components in that particular channel). the output transistors are in pairs for each channel, so you will have an "A" and a "C" (or "B" and "D") transistor for each channel.