FYI to people having a go at these BX series amps:
At the bottom of the main board (hidden underneath) there is usually a cap or two secured by that disgusting amber glue (my personal favourite electronics HATE item
)
In most cases the affected board tracks may be almost totally eaten away and or intermittent temperature dependent 'bridge work' is going on to cause audio hissing n crackles, and other unexplained headaches
i.e. I would strongly suggest to sort this out first before moving on to the next troubleshoot/repair procedures
fwiw the gunked greencaps are usually ok and reusable after a clean up, and solder some wires or whatever on the eaten tracks.
Check the amp for other 'innocent looking'
glue affected areas too, and sort them out asap
I have saved a few this way without troubleshooting any further for issues,
and own a couple, nice cheap decent linear performance amps at low to moderate loudness levels with efficient loudspeakers
and not too shabby waveforms on the oscilloscope