NES-PCB-11 weird modification found

[nanochess]

Recently I've got a NES for $1 USD without power supply but with the two controls, I've cleaned it and managed to get it working.

 

Apparently it was discarded because the dirt in connector prevented cartridges to work and furthermore the cartridge port was wrongly put together so it didn't accepted cartridges.

 

Only one control works and I've been able to put right the cartridge port.

 

The point is that I've discovered that the power light doesn't work, I've followed the LED traces through the PCB upto the mainboard (NES-PCB-11 from 1987) and I've found a kind of modification that I couldn't discover in Internet.

 

So before undoing any connections, I would like to know if someone knows what is this modification.

 

Note the yellow cable, the resistor and a soldered jumper in the big connector that I'm supposing brings LED voltage to zero so it doesn't turn on.

 

[+kevtris]

Recently I've got a NES for $1 USD without power supply but with the two controls, I've cleaned it and managed to get it working.

 

The point is that I've discovered that the power light doesn't work, I've followed the LED traces through the PCB upto the mainboard (NES-PCB-11 from 1987) and I've found a kind of modification that I couldn't discover in Internet.

 

 

If I had to guess, I'd say that they disabled the lockout chip. The LED on the NES is connected to the reset line to the CPU. That's why it flashes when the lockout chip detects an error- it is resetting the and unresetting the CPU (hence the typical flashing). The reset button on the NES is the wrong polarity (active high) compared to reset on the CPU (active low), so it looks like someone connected the reset button to the /RESET line on the CPU, and grounded the other end of the reset button, and in the process disabled the LED (you will probably find some hacks on the little button/LED board).

 

I made a mod similar to this back in the day because I didn't know you could just cut pin 4 of the lockout chip to disable it. If you remove that wire, you will find the reset button probably won't work any more. Fixing the LED is possible but I guess they figured it wasn't worth it.

[nanochess]

Thanks a lot, kevtris!

 

I suppose I can leave as it is, I think this modification is a lot better that cutting pin 4 of lockout chip.

 

I can live with the off LED.