I received the new power amps yesterday, and replaced this one just now.
(Yesterday morning i followed the audio signal all the way to the power amp, so it should be the power amp.)

I also added a heatsink so that the new power amp may hopefully live longer.

Tested again, and the sound is back. 🙂
(There are some minor crackling noices though, so i’ll have to check/replace the caps in the audio path.)

This is a “Bomb Jack” arcade game pcb.
It´s a clone (“bootleg”) of the classic “Bomb Jack”.

It boots and plays, but without sound.

The sound is handled by a Z80 CPU with a 2764 EPROM containing the sounds, SRAM and three AY-3-9810 sound chips.
Power amp is a M51516L.

Probing pins on the Z80 shows that clock (3 MHz) is present, /RESET and /HALT is high.
/RD, /WR and /MREQ are pulsing as they should.
D0-7 and A0-14 are pulsing.
(A15 seems to always be low, but in the schematics it seems it’s not connected to anything special?)
It looks like a small ‘X’ is scraped on the Z80 (?), so someone earlier may have suspected it to be faulty.

Probing the AY’s gives that clock (1.5 MHz)is present, CH1-3 on several of them seems to output something that seems to match when a sound should be playing.

Touching the power amp with my finger gives no static at all to the speaker.
(The volume pot seems to be ok when measured.)

I have ordered 2 new power amps, and will replace it later. (Ordered one extra to have as a spare part.)
While i wait for them i will try to follow the sounds towards the power amp, to see if it gets lost somewhere on the way. 🙂