shmups.system11.org

I finally got ahold front loader NES with this problem. It's a silly bug in the FPGA firmware. When I enabled the PLL I mistakenly connected the FPGA PLL reset to the console reset signal. So when the console reset time is extended by changing the capacitor on the motherboard, the reset time of the FPGA is extended too.

Fortunately there is a simple fix. There is a redundant reset signal generated on the NESRGB board already. This is because the Famicom consoles don't reset the PPU, the reset pin is tied to the 5V supply on these consoles. The fix is to just cut off the RESET pin off the NESRGB board assembly, isolate it, and connect it to +5V.

Here's the procedure:

1. Cut pin 22 (RESET#) off the NESRGB board assembly.


2. Put some electrical tape over pin 22 of the socket on the motherboard.


3. Solder a 1k resistor between pin 40 (+5V) and pin 22 (RESET#) on the NESRGB board. If you don't have a resistor handy, just make a direct connection with some wire. Install the NESRGB board back in place on the motherboard and use a multimeter to measure the continuity between pin 22 on the motherboard and NESRGB board to make sure it's not connected.

Just tried this on my NTSC front loader to success! no more flashing LED7 and booted right up to pallette 1! after a few minutes I lost audio and the screen wanted to fade out to blue but came back I am thinking my voltage regulator is bad. I do have the spare regulator from the kit hooked up as well.

Tomorrow when I have more time I can try a replacement regulator that I got recently that is rated for 2a instead of 1a which should help the situation. If it continues further I am thinking capacitors on the power supply are to blame. Can anyone chime in and let me know if I am on the right track?

Seems to have worked on my PAL Frontloader!

I would say it might be better to completely remove the pin (including the plastic spacer) to avoid having to drop electrical in there as a fix. Electrical tape has a tendency to slip off in warm to hot environments, and isn't exactly the cleanest of fixes.

That is a good idea, I'm having further issues with my nes video output disappearing to the solid background color and sometimes coming back it kinda like fades in and out with horizontal lines to the background colors. I'm thinking I need to do a full recap ok my nes to fix this issue. While doing so I'll address that area by removing the header in that one space entirely.

Is this for the “interrupt detection bug” issue? I have a few motherboards that are exhibiting the exact behavior for this bug and don’t know how to fix it.

No this is a different bug with boards 22.38

New 78S05 did not fix my video issue but slightly improved it the audio stayed this time around but just the sprites faded out. I was using Mario bros. 1/duck hunt cart to test, after about 5 minutes of game play the sprites on screen will "fade out" or do some bands of missing sprites or interference, sometimes part of the sprites will come back and then leave. The game is still working and inputs still work I can hear Mario jumping etc. Not sure how to describe this problem. I plan on doing a recap on my NES now to see if that is the problem. If still there is the issue after that I am not entirely sure what is wrong.

Next step would be to check the VRAM and see if perhaps that has gone bad or is going bad. I had an unfortunate issue where the VRAM in a front loader got absolutely fried somehow. Replaced the VRAM chip and it came back to life. I believe replacement chips can still be had from Digikey or Mouser, though it's been a couple of years since I did that.

@viletim will you have time soon to write up about the 2231 modification board for us? The referenced Monday in your previous post about this was December 5th, but unless I missed it somewhere I don't see that - just the MCU update information. Thank you for your time, hope you had a wonderful Christmas.

I'm having an issue with my NESRGBv4 install that is very similar to this issue, but the steps in the post have not resolved the problem. Wondering if anyone here has any ideas. Here is the situation:

- NESRGB v4, 22.38 install on NTSC front loader with voultar QSB for multiout, expansion audio, external regulator, and YPbPr add-on board.
- Initially, LED0 would be solid and LED7 would flash slowly
- Jumpers J1, J6, J10, and J5 shorted
- I have tried every combination of enabling/disabling jumpers except J5 which is needed for NTSC, issue does not resolve. I have also tried enabling/disabling NESRGB board via controller when J1 is shorted.
- Tried shorting J3 to use NES voltage regulator, issue does not resolve.
- Verified C8 capacitor was replaced with 220nF and also tried with different 220nF, issue does not resolve.
- I performed the steps from the viletim in this post (cut pin 22, isolate with electrical tape, verify isolation, install 1k resistor between pins 40&22, verify continuity) and issue did not resolve
- As others in the post suggested, I installed a 100pF capacitor between pins 13 and 20. This resulted in LED0 remaining solid, but LED7 no longer blinks. Stock composite out displays no image, but output is grey suggesting NESRGB board is doing something?
- After removing the 100nF capacitor, LED7 still no longer blinks but LED0 remains solid. Stock composite goes back to normal. 

I've verified wiring is correct. This is the 2nd time I've installed a NESRGB4 in an NTSC front loader with this exact configuration. In my first installation, I had the bug requiring the pin22 fix which resolved the issue. Both 22.38 boards. 

It sounds like a reset timing issue but I'm not sure what other combination of capacitors are needed to get the NESRGB board enabled.

Update that was posted in the main NESRGB thread:
I have good news and bad news.

The good news (for everyone): I can confirm the latest batch of NESRGB4 22.38 boards with this issue is fixed with both the 22pin fix and MCU 2.1 update. My NES is outputting YPbPr perfectly and is able to palette switch and reset via controller. I haven't tested RGB yet as I haven't connected my Multi-out, but presumably it works too.

The bad news (just for me): the NESRGB4 22.38 that I originally had this problem on appears to be toast.

It was not able to receive the MCU 2.1 update. I made sure to use the 1k resistor from GND to the update pin. I tried two different PCs, two different TTL USB sticks, and powering the board via 5V pin and through the NES. I could not get this one to accept a firmware update at all (2.0 or 2.1), but I was able to update a 2nd (now working) NESRGB4 22.38 board to MCU 2.1. They both performed identically with the same problem initially.

I have a 3rd board that has not been installed yet, but I was able to update to MCU 2.1. We'll see if it also works correctly.