The venerable Nintendo Entertainment System, or NES for short. This particular specimen doesn‘t work. Bummer.
#retrogaming #nintendo #nes
The venerable Nintendo Entertainment System, or NES for short. This particular specimen doesn‘t work. Bummer.
The venerable Nintendo Entertainment System, or NES for short. This particular specimen doesn‘t work. Bummer.
#retrogaming #nintendo #nes
25 Comments
root42@chaos.social · 4 pts · 1y
The NES is a pretty simple machine actually. At the hear we find the RP2A07A CPU clocked at about 1.66 MHz for a PAL machine. It is basically a 6502 with some augmentations. The clock input is 26.6 MHz on PAL and internally divided by 16. It has two audio out pins, one for square wave, the other for PCM and triangle/noise. Attached is a 6116 SRAM chip with 2KB capacity.
root42@chaos.social · 2 pts · 1y
The other part of the system is the RP2C07 PPU. This is the graphics engine of the system. It‘s the chip that produces the video signal, draws all the tiles and sprites. It too has access to dedicated 2K of SRAM in the form of a 6116 chip. On this board this chip is a different variant by Goldstar (today known as LG).
In the lower right corner a small Nintendo branded DIP16 chip is visible, the so called CIC, which handles the reset circuit and also deals with copy protection.
root42@chaos.social · 2 pts · 1y
The board from the first post was actually working. But this one is really broken. I swear! It has no video output. So let’s check what’s going on. I connect my scope probes to Vcc and clock pins on the PPU.
root42@chaos.social · 2 pts · 1y
Oof. That doesn’t look so great. The Vcc is exactly where it should be (cyan curve) but the clock is a flat line (yellow curve). No wonder there is no video output. Another issue: the working board has a consumption of 400mA while the broken one uses 800mA. Something is sinking quite a bit of power.
root42@chaos.social · 1 pts · 1y
The oscillator circuit is not that complex. The 51pF capacitor on the right goes off to the PPU while the left transistor drives the CPU.
root42@chaos.social · 1 pts · 1y
The clock signal at one side of the capacitor looks slightly wonky. On the other side of the capacitor it is completely gone. As there is nothing else between it and the PPU I think we have a dead PPU, pulling the signal down. What a bummer.
lasse@social.tchncs.de · 1 pts · 1y
@root42@chaos.social that's not slightly wonky, that's not even a clock signal! I'd expect some serious edges and a lot more square-ness, you know... and some serious amplitude, not just a couple of millivolts of noise.
Remove that coupling capacitor and see if that fixes the clock signal.
root42@chaos.social · 1 pts · 1y
I have now a replacement CPU snd PPU. But even with those I still get a grey screen.
root42@chaos.social · 1 pts · 1y
What I noticed: on the Video bus side of the PPU there is ZERO activity. And no CS for the PPU. So I suspected the LS139 which generates the CS. But minipro says: all good!