How to repair Sony STR K840P in protect mode!

Here I trace out the reason for this unit being in protect mode and with parts becoming harder to get for older models I find an alternate solution! Tools I use - Soldering Quick 861DW hot air station Duratech TS-1640 solder iron Multimeter RMM760D - can be found under many name badges Microscope Luzky Zoom 3.5 - 90x simul-focus single boom stand trinocular stereo microscope Camera - Lucky Zoom HD 14MP Oscilloscopes Siglent SDS 1102CML 100MHz 2CH Philips PM 3305 35MHz 2CH Bench supply Powertech MP-3086 0-30V 3A TL866II PLUS universal EEPROM programmer