A year ago, I bought a top loader that appeared to be in good shape off eBay. My goal was to build a little composite video amp and give it as a gift. I'm just a hobbyist in electronics stuff, I have a lot of experience soldering/desoldering/troubleshooting but have no formal training.
Initially the NES seemed to work, but was intermittent. From power on, it may take several resets before I'd get a game to load. Additionally the 7805 was pretty hot to the touch, even on the heat sink. I did not notice excessive heat from the CPU or PPU. When I measured the +5v rail, I would get something closer to +3.6v. I decided to replace the large electrolytic capacitor, still got 3.6v. I took the 7085 out of circuit and it produced +5v, but under a ~200mA load it would get very hot and the voltage would drop. I believe that chip should handle more than 1000mA without a voltage drop.
Easy fix, right? I replaced the 7805 with a brand new one, and suddenly my +5v rail was +5v (and the regulator seemed to run much cooler). Also, the unit would load the game every time. I was pretty pleased, I fixed it!
On to the next problem, jail bars(or at least reducing them). I started replacing the other electrolytic caps(C1, C3, C11) around the board with new ones, and testing the extracted ones in the process. All the caps were in spec, but here's where stuff went bad:
I turned on the top loader when at least one of the capacitors was out of circuit (I think it was C1, the .01uF cap near the cartridge slot). The unit produced solid color video, but a ton of audio noise and a big horizontal black line in the center of the screen. I put the cap back in circuit (the original one, with the correct orientation), but the broken video/audio persisted.
At this point I'm looking around trying to figure out what I bumped loose and I can feel heat coming off the board from a foot or so away on my face. I touched the CPU and the PPU, and the PPU was burning hot. Needless to say I was pretty sad.
So kinda long-winded to this point, but I'd love to know what I did wrong.
- did I cause a failure by operating the top-loader without one of the electrolytics in-circuit?
- was the PPU failure imminent from the way the old 7805 was loaded down/failing, but replacing the 7805 was able to supply the extra current to finish bricking the PPU?
I'd still like to repair it, but I'm hesitant to sacrifice a working NES to get a PPU for a top-loader that may burn that PPU to a crisp, too.
- I just ordered an UA6538 on order from aliexpress to see if I can at least get video without killing a real PPU. I must sheepishly admit that I ordered a UA6527P a few months back thinking it was a PPU swap when in fact it's the CPU. I realized my mistake writing this post. (needless to say, it didn't work as a PPU)
- Anyone have experience with throwing caution to the wind and just replacing the PPU and it working, or is my unit a possible serial PPU killer?
Thanks in advance, I've learned a lot from reading past posts here and was impressed by how helpful you all can be.
Initially the NES seemed to work, but was intermittent. From power on, it may take several resets before I'd get a game to load. Additionally the 7805 was pretty hot to the touch, even on the heat sink. I did not notice excessive heat from the CPU or PPU. When I measured the +5v rail, I would get something closer to +3.6v. I decided to replace the large electrolytic capacitor, still got 3.6v. I took the 7085 out of circuit and it produced +5v, but under a ~200mA load it would get very hot and the voltage would drop. I believe that chip should handle more than 1000mA without a voltage drop.
Easy fix, right? I replaced the 7805 with a brand new one, and suddenly my +5v rail was +5v (and the regulator seemed to run much cooler). Also, the unit would load the game every time. I was pretty pleased, I fixed it!
On to the next problem, jail bars(or at least reducing them). I started replacing the other electrolytic caps(C1, C3, C11) around the board with new ones, and testing the extracted ones in the process. All the caps were in spec, but here's where stuff went bad:
I turned on the top loader when at least one of the capacitors was out of circuit (I think it was C1, the .01uF cap near the cartridge slot). The unit produced solid color video, but a ton of audio noise and a big horizontal black line in the center of the screen. I put the cap back in circuit (the original one, with the correct orientation), but the broken video/audio persisted.
At this point I'm looking around trying to figure out what I bumped loose and I can feel heat coming off the board from a foot or so away on my face. I touched the CPU and the PPU, and the PPU was burning hot. Needless to say I was pretty sad.
So kinda long-winded to this point, but I'd love to know what I did wrong.
- did I cause a failure by operating the top-loader without one of the electrolytics in-circuit?
- was the PPU failure imminent from the way the old 7805 was loaded down/failing, but replacing the 7805 was able to supply the extra current to finish bricking the PPU?
I'd still like to repair it, but I'm hesitant to sacrifice a working NES to get a PPU for a top-loader that may burn that PPU to a crisp, too.
- I just ordered an UA6538 on order from aliexpress to see if I can at least get video without killing a real PPU. I must sheepishly admit that I ordered a UA6527P a few months back thinking it was a PPU swap when in fact it's the CPU. I realized my mistake writing this post. (needless to say, it didn't work as a PPU)
- Anyone have experience with throwing caution to the wind and just replacing the PPU and it working, or is my unit a possible serial PPU killer?
Thanks in advance, I've learned a lot from reading past posts here and was impressed by how helpful you all can be.