Faulty Nes consoles

I was asked to fix 2 nes consoles, the guy described the symptoms (flashing red light and resetting screen), so yeah I figured that will be simple enough

but after he dropped them off I tested them and indeed it was as he described, so I first tried cleaning the contacts and disabling the lockout chips on both, but still no luck on either, then I tried a few other games and eventually Kick Off worked fine on both of them, so I figured I would try clean them again...but still nothing, then I had a look in the bag he gave me and it turns out he had a 12v power supply in the bag, I'm guessing he has blown something on the console causing most games to not function, does anyone have any idea what might have blown and how to fix it (if possible)

 

Take them apart and see if anything looks burnt out or melted.

 

I doubt anything has selectively burnt out that just stops a few games. More likely bad cart slot.

 

yeah but its both systems having the exact same symptoms, only game either will play is kick off, I will try swapping the cart reader over from a working system just to make sure though

and nope I couldn't see anything damaged when I opened them to disable the cic chip, but I wasn't looking very closely so I will double check that too

 

Is it the games that are broken?

 

nope they all work fine on another console, the guy didn't seem too familiar with old consoles and said he found them in his loft and couldn't get them on, so it just kinda seems like he found a random power supply to "test" them with and managed to cause the same damage to both systems

anyway I will try taking them apart again and swapping the connector from a system I know works, but It does feel like its just going to be a fault caused to something really specific for both systems to have the exact same issue

 

I think 12V is within the parameters of the 7805 voltage regulator inside the NES. Lots of things could go wrong in the NES. The most common thing is a bad connection with the cartridge either being the fault of a dirty cartridge or dirty or bent connector pins.

I got a broken NES recently that worked but the graphics were severely messed up. It turned out that it had bad solder joints on the 2KB SRAM used for Video RAM. After applying fresh solder it worked perfectly. That's just an example that many things could go wrong. But the connector or dirty carts is #1. The 12V power supply shouldn't have damaged anything. If the connector isn't the issue then it's time to do a good look over the entire PCB.