May have missed it but have you tried pulling the key inputs
& using the remote. If its an SMD no easy way. Any TAC switch
is suspect for leakage. On older sets we would unhook most of the micro
& just keep the ON/OFF path. Then hook things up til it stops working.
Almost always a TAC switch or little disc.
Also check & be sure you are getting a good RST, you can also
force it to test ( RST or NOT RST ). Lytic cxaps & RST transistors
the usual perps here.
BTW you are covering things well but did you pull the batteries from the
remote ?
73 Zeno
LFOD !