So I picked up a GPM-02 Famicom to install an RGB mod in and while I was doing the pretesting to make sure it worked it decided to just up and quit on me. This is before mod work began mind you so it was not a botched install. When powered on the PCB is fluctuating between .25 and .5 volts on the power line. At first I thought maybe the regulator was the culprit but even after removing the RF box and powering the PCB with a straight 5 volts the 5 volts line reads between .25 and .5 volts when powered on. Next I went and tested 5 volts straight from the power jack (I am testing with a straight 5 volts setup to eliminate other possible faulting parts with the RF box). When off the power jack reads a steady 5 volts but when powered on the 5 volts line drops to to between .25 and .5 volts even from there.
I decided to desolder the PPU and tested it in my US front loader and it works OK. I have not tried replacing the CPU yet though. The problem is definitely with something on the Famicom PCB itself, I just cant figure out what. Has anyone experienced a similar issue?
My colleagues are experting in fixing broken famicoms, I'll ask them...
the infamous regulator has built-in short circuit protection. It looks like it applied this protection. Highly recommend to at least inspect the PCB visually. Also double check the polarity of power lines/mod you'd applied