Klipsch R-12SW fixing

[Veketti]

Dear All,

I'm trying to fix broken Klipsch R-12SW active subwoofer and have already measured that its power supply is ok. It supplies 35VDC and 5VDC, so I assume the amplifier is the culprint. I measured the power transistor TIP31C and found out that pin 2 and 3 were short. Just noticed that they are soldered together (first picture). So this is always on. I assume this shouldn't be the case because why put transistor there if it's always on? However I'm thinking could the solder melt and short them? Doesn't sound very plausible. Should I cut them separate and test?

Visually didn't find any issues, all components look ok. However R36 (3rd picture) has been very hot as the other side of the pcb under that has turned brown. However I'm still measuring 460ohm for this so it hasn't burned open or short. Unfortunately didn't find any schematics for this.

Thank you in advance.

[m k]

What is the overall orientation?
Hot can be very hot.

Heatsink connection is also a bit less than optimal.

[Veketti]

Those legs point down, so in theory that solder could have run down due to overheat. For the heat dissipation, there is extra plate which presses these two components to the plate, which is removed in that picture. Anyhow, I changed that power transistor to a new, but unfortunately that wasn't the culprit. It does not "bang" anymore when power is plugged, but after a while the speaker starts knocking at around 0.5 Hz frequency.

[m k]

So something is crawling or some unwanted frequencies are summing.

I remember 50/60Hz TV timing something from the past but that's too fast.