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Technics HD501 Stops Playing

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I have a Technics HD 501 mini HI-FI. When it has been playing for a while (around 1h at best) it suddenly makes a popping noise and stops playing. The whole system freezes and I have to switch it off - it doesn't let me take out the CD, change the volume or anything other than switching off. If I don't do this in a few seconds it makes more popping noises. If I try to switch it back on straight after having switched it off, it does the same again after playing for a few seconds. If I leave it for some hours, it will play for a while again. This happens with CD but also if I connect my phone or play the radio.

Has anyone had this problem before? Any idea what might be the causing it? It seems like it could be the amplifier. No one is too keen to repair it, as it is quite old now, but I do love this sound system!

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Sounds like the internal power supply to me if the whole system freezes, rather than just an audio issue.

Possibly the power supply going into shutdown through a heating issue or a component that drifts out of tolerance with heat.

Could be just one of the rails, possibly a controller logic rail (say +5V) if there are signs that "something" is still on but the system is otherwise non-functional. The popping might be due to the rail rising again briefly before shutting down again.

Probably not a user repair, but it would be disappointing if a general electronics service technician wasn't prepared to at least have a look. Diagnosis might be tricky but I suspect the fault once found would be relatively easy to fix.

Being able to offer this Service Manual, that does at least have the schematics, might help (and possibly around the circuit of Q101):

Service Manual: https://elektrotanya.com/technics_se-hd501.pdf/download.html

Needs more diagnostic work to narrow down the problem area. It looks like a modular system, so if you unplug various sections and test, what can you ascertain about when the fault shows and when it doesn't? (Accepting with the CD disconnected you can't play a CD...)

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