SNES in continuous reset loop
Hi, I bought a SNES on ebay recently that goes into a continuous reset loop when I try to play any game. It's sort of random how fast/often it happens, and some games will reset a lot faster than others. For example, SMW resets exactly after the "Nintendo presents" text appears, while other games like Super Metroid only do it when it gets to the menu screen, and not always consistently. I've done all the basic troubleshooting, including cleaning the cartridges/slot, trying different power supplies, making sure the power connection is good, and everything was fine.
So I decided to dig deeper and look at some schematics to try to figure out what's going on inside. I measured the voltage, which is a constant 5v (slightly higher though at 5.042v) and it doesn't change at any point. I also measured the voltage coming from the reset button and the reset line on the CIC chip, and the reset signal is not coming from there. What I did find though, was that the T529D chip (which is supposed to send a pulse on the RESET line on all the processors when a system reset happens) was in fact intermittently sending a pulse. Thought it might be faulty, so I swapped it with one from another console but that didn't fix it. As an experiemnt, I tried shorting the pins between the ground line and the out line on the T529D for a few seconds, and I was actually able to get it out of the reset loop and everything working fine until I turned the console off again. So at this point, I'm looking at the schematics and the only other thing I see that's capable of sending a reset signal on that line is the PPU and the DSP. Is there anything else I might be missing, or should I assume that one of the processors is faulty?
Here's the schematic I'm using. The reset chip is labeled U11.
https://gamesx.com/wiki/lib/exe/fetch.php?media=schematics:snes_schematic_color.pdf
The reason I really want to fix this is because it's a 1CHIP console, which are not easy to find or cheap, so any help would be greatly appreciated!
So I decided to dig deeper and look at some schematics to try to figure out what's going on inside. I measured the voltage, which is a constant 5v (slightly higher though at 5.042v) and it doesn't change at any point. I also measured the voltage coming from the reset button and the reset line on the CIC chip, and the reset signal is not coming from there. What I did find though, was that the T529D chip (which is supposed to send a pulse on the RESET line on all the processors when a system reset happens) was in fact intermittently sending a pulse. Thought it might be faulty, so I swapped it with one from another console but that didn't fix it. As an experiemnt, I tried shorting the pins between the ground line and the out line on the T529D for a few seconds, and I was actually able to get it out of the reset loop and everything working fine until I turned the console off again. So at this point, I'm looking at the schematics and the only other thing I see that's capable of sending a reset signal on that line is the PPU and the DSP. Is there anything else I might be missing, or should I assume that one of the processors is faulty?
Here's the schematic I'm using. The reset chip is labeled U11.
https://gamesx.com/wiki/lib/exe/fetch.php?media=schematics:snes_schematic_color.pdf
The reason I really want to fix this is because it's a 1CHIP console, which are not easy to find or cheap, so any help would be greatly appreciated!
Comments
If cartridge connector pins are removable on that board version, pop the pin connector off and see if there's anything in-or-under it shorting out.