My advise would be to disassemble according to the instructions [[Device:Nintendo Entertainment System|on here]]. Take the cover of that shields the RCA connection (TV out etc) and take a close look at all the solders as well as the resistor and the PCB. Anytime it works when you apply pressure would intake a microcrack in the solder points etc. It is hard to determine exactly what is going on, but you will have to start somewhere. Attached find the schematic for your console. Good Luck and let us know how you are progressing. Keep those consoles alive :-))
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