My friends Squier Champ 15 had a problem - it didn't produce any sound. Red LED was illuminated but there wasn't even a hum from the speaker. My first guess was that a power stage was damaged. After opening up the Champ 15 reveled its uncomplicated construction:
One-sided PCB with two double operational amplifiers and TDA2030A monolitic amplifier. I searched for any sight of thermal events and measured supply voltage which turned out to be correct -20V/+20V. After feeding input 1 with audio signal from a laptop I measured with an oscilloscope that there is a correct signal on pin 1 which is input of the TDA2030A (it means that a preamp is working fine). There was amplified signal on the output of the TDA2030A to, so I moved on to connection between amplifier, speaker, and two connectors for headphones and a external speaker.
Plugging in headphones should disconnect the built-in speaker to make the combo silent, in case of this amplifier the problem was that one terminal of the speaker was disconnected because of defective headphones connector. Pair of normally shorted pins which should be shorted when nothing is plugged in was disconnected. I hard-wired them to check if this was it. Amplifier started to work.
I didn't want to replace defective connector so I've just fixed it. I desoldered and took out an elastic metal part which wasn't switching reliable enough, bent it so it was tighter, put it back and voila! Squier Champ 15 is working now.
This is mentioned elastic metal part, I am holding it with tweezers.
Metal part is on its way to be fixed:
Metal spring after bending:
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