How to diagnose and repair a radio?
A friend gave me a Marine VHF Radio Receiver which is working badly, and asked me if I can look into it and try to repair it (I'm not going to charge him).
The first time the radio is turned on, the reception works OK, but after a few minutes the reception dies, and turning it off and on again immediately won't fix the issue. I have to wait a few more minutes with the radio turned off to again start receiving OK. The squeltch is always at minimun, receiving noise.
When the radio dies there is a high pitch noise coming out of the speaker. The external speaker connection is wired directly to the same internal speaker circuitry.
Since the problem goes away after a few minutes I guess the issue is a broken component, like a capacitor or resistor.
I have no electronics background, just a few soldering skills. I want to learn how to repair stuff the DIY way. A few weeks ago I repaired an audio amplifier. The problem was simple, a burned track on the PCB.
What are the steps required to pinpoint the problem? My toolset is limited, I have no oscilloscope, and no capacitance and inductance meter, just a couple of cheap multimeters.