Audio Systems: Trunk mounted amp doesnt turn off, first transistor, radio battery

Question
-------------------------
Followup To
Question -
2002 Pont Sunfire Monsoon radio. Battery kept going dead. Noticed hiss in speakers with everything off. Checked voltage on "radio on" wire going to amp. 12+ with radio on but only drops about 1/2 volt (11.5+) when radio shuts off so amp remains on. Possible corrosion in radio. Car was closed up with wet carpeting for quite awhile. Thought corrosion might have bridged a circuit inside radio. Disasembled and cleaned all circuits I could find but did not help. Is there any thing in the computers that could be providing power to the "radio on" wire? New radio?
Answer -
Jay,
the amp on signal comes from the stereo when you turn it on. Many times I have found partiality shorted power on control transistors. With these shorted transistors the power control lead to the amp will not turn off fully. If you do not have a schematic for this stereo you can trace the wire to the pin in the connector that is for amp on. All you need to do now is to follow/trace that circuit in the stereo until you come to the first transistor, this may be the one that is shorted out.

TOM,
T&D ELECTRONICS
tdeser@zoominternet.net

Thanks, Tom
Are you talking about one of the transistors fastened to the large heat sink on the side of the chasis? I did disassemble the radio again and sprayed the area around those transistors with the cleaner and kept taking readings between the power pin and the "amp on" pin and readings went from k-ohms to m-ohms indicating progress. I reassembled the radio but left the screws on the heat sink loose intending to re-apply heat sink grease before I tightened them and the radio now works properly. I wonder what is going to happen when I re-tighten the screws. It might be that the stress on the transistors when tightening the screws is aggravating the short. Is it possible to obtain a replacement board for that radio ("UP1") if I need it?


Answer
Jay,
Use a magnifier to take a close up look at the pins on this transistor on both sides of the circuit board. With no power hooked up to the radio use some kind of tool to remove any corrosion between the pins. try retightening the screws to see what happens.

TOM,
T&D