NES-001 cap replacement guide for the av power module

[jcarlos]

The 74LS373 are Latches 3 states?.

[lidnariq]

Yes, but the NES doesn't use the 3-state capability.

If you look at the pattern on the screen, the Mario sprite is correct for two scanlines, then wrong for two. Similarly, the background tiles are correct ... maybe ... for two tiles horizontally, then wrong for two.

So I think there's something wrong with A2 A1, but I can't tell whether that's the '373 or the cartridge connector.

[jcarlos]

I have measured in both mainboards without power supply from ground to each of the pins of the 74LS373 and I only appreciate a curious difference, in the 74LS373 with the black clamp on ground (10) and the red one on pin 11, on the bad board it gives infinity While on the good side the multimeter cannot measure but if I reverse the red ground and black clamps on pin 11, I get a big difference, on the good mainboard I measure 4.30K ohms and on the bad one I measure 1.9 M ohms. The multimeter does not have scales, it is automatic, a FLUKE. The other pins correct. I don't know if it's a reason to replace the 74LS373.

[jcarlos]

A2 is an address line between the 74LS373 and the PPU? There may be a bad connection with the memory of the PPU because it was difficult for me to remove it and some pads were lifted, but I solved it, and checking continuity seems to be all fine. What do you mean by A2?

[lidnariq]

AD2 goes from the PPU to the 74'373, where the +ALE signal marks when the bus holds A2 (instead of data), and the 74'373 holds on to A2 the rest of the time.

[jcarlos]

Pin 11 of the 74LS373 is LE (Latch Enable) is enabled with 5V, and goes to pin 39 of the PPU which is ALE. I do not know if there may be the fault

[lidnariq]

PPU D0 (rightmost pixel) and/or A... oops, I've been brainoing, I meant to type "A1" -- could be problematic. I can't really tell you more specifics. You'll have to poke around and see more specifically for yourself.

You might find Krzysiobal's reverse-engineered schematic helpful: viewtopic.php?t=18861

[jcarlos]

I have measured continuity of both AD2 and ALE and they arrive at the 74LS373, it seems that the connection failure is not. Could it be that this input is faulty and latches are not enabled with the ALE signal?

[lidnariq]

No, because most of the other bits are working. If they weren't, you'd get much more distortion. (Also, I'd made a mistake, check A1 and not A2)

[jcarlos]

Indeed, it was pin A1 that goes from the PPU (pin 37) to the 74LS373 (pin 13), there was a bad connection, I put a jumper and that's it. She wanted to thank him for her essential help, without her she could not have done it. Thank you.