Finally got the £20 non-working TNT 150 on the bench.
Replaced the cap and rectifier (forgot to take photos), chassis back in, speaker reconnected, flick the switch... no loud pop followed by constant hum, which is good! Sound when plucking a string is fizzy, barely audible and when above 1 on power amp volume (regardless of pre level) lights up the speaker protection LED.
So the two options are there's still something wrong with the amp, or the speaker's blown. Given the condition when I got it the latter is more likely, but kind of want the former as that's a cheaper fix (though it takes more effort!).
