The closest book I have is a '97 service manual, but it should be the same circuit. The two rear speakers and the two door speakers have little amplifiers bolted onto them. They will have four wires in their electrical connectors. Tapped off of them are the two rear pillar speakers and the two dash speakers. Those do not use amplifiers. They will work even if power is lost to the amps. That means you do not have an amplifier problem. Just in case they changed that for '98, you can verify that by removing one of the speakers with an amp and measuring the voltage on the power and ground wires. The red / dark green must have 12 volts when the ignition switch and radio are turned on. The black / dark green must have 0 volts.
The next thing to observe is if the clock goes back to 12:00 each time you turn on the ignition switch. If it does, the memory fuse is blown but there should be other things not working including that air bag light should be on. We'll head that way if necessary. If the clock maintains its memory, the two power circuits are working.
The only thing I can think of in that model that can cause no sound is a cracked front circuit board. That is REAL common if UPS gets a hold of it and bounces it off the floor! The volume **** gets shoved into the radio and shatters the circuit board. I've repaired a few dozen for that. It can be very time-consuming to follow all the tiny circuits with a magnifying glass. I've spent as much as seven hours repairing those boards. If it's really badly damaged, I have good used ones to pop in instead. Another common cause is from someone hitting the volume **** in frustration when the buttons don't work right. I repair those buttons too.
It's always possible there is a shorted audio amplifier IC inside the radio. That is very rare on the Mitsubishi-built radios. Depending on the model, one of them either runs the front speakers or the left speakers. Sometimes when one shorts, it puts a voltage on the "muting" circuit which turns the other one off. That is the circuit that cell phones are tied into.
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Sunday, April 24th, 2011 AT 10:40 PM