I'm pretty much guessing here... but I think it's part of the AC\DC detection function?
Pin /I-HOLD on the CPU maybe means Input-HOLD, eg: prevent buttons from functioning while the pin is low. What voltage is on that pin?
Or maybe I just means it's an input pin (schematic symbol > on pin confirms this) and it's for the HOLD function.
See above the " -12- " marking on page 12 schematic where it says "AC & DC DET"
/HOLD line seems to be controlled by Q060 on other board, which seems to be controlled by Q061\Q062. It looks like these are controlled via several different inputs, including something from AC supply via D063 and D064.
it may also detect faults via Q063 and Q064, one of their inputs trace back through D062 and D065 to the speaker outputs, and also thermal protection via Q059 and TH101\TH102 on the output transistors.
So perhaps your fault detect circuit is faulty. Check for more dry joints etc perhaps in those areas.