I have an RCA STA 3900 stereo reciever that wont turn on. Standby light is on. Tried resetting it from the back but didnt work. Please advise

probably the power supply

Hi,
Did you ever find the schematics? I am also troubleshooting my STA 3900.

Sounds like your output transistors are bad, what audio you are hearing is coming from the driver transistors. Could be any number of thing else going on. Try selecting only one channel " a or b" at a time and see if the volume increases. It could be that your speakers have gone bad .If you have other speakers I would try that before taking it to a qualified repairman.

Unplug the unit,wait approximately 5 minutes,remove the top cover look for the place where the power cord enters the unit.the fuse will be on the board next to the power transformer, should be labeled F1 and a 4.5-5 amp 125/230v glass type fuse

it is either a short on one of your speaker lines or it could also be that one of your PCI's have blown.

Looking for a replacement remote control?

you might have blown out all your electrical under your dashboard you might want to check your fuses in your car.

Generally speaking, an amp attempts to protect itself from heat, shorts, overloads and operator exuberance by refusing to turn on or stay on.

Overloads can be from excessive periods of high output or marginally low impedance loading by the speakers; and shorts would be wiring issues or a speaker blowing up.

You should be able to feel if it's hot. WHY is it overheating? Make sure it has sufficient ventilation on all sides and that vent holes are not blocked by dust balls. Ensure the fan (if equipped) is running as designed (some only operate on demand). Clean dust and debris from it.

If the amp comes back on after cooling, you're lucky. They only have so many self-protection cycles in their lives so continuously resetting or cycling their power without addressing the cause can do more harm than good.

If it protects immediately on a cool power up you should disconnect the speaker connections and try it 'nekkid'. If it comes up then diagnose which lead(s) are shorted. If it does not come up the problem is internal and should be left to an experienced and competent hands-on tech.

POWER SUPPLY BLOWN FUSE CAUSED FOR A BLOWN OUTPUT TRANSISTOR , DO YOU HAVE THE NUMBER OF THOSE TRANSISTORS??

there are 4 caps that need to be replaced. http://chrisandnat.com/projects/blinkingtv/blink.htm