NESRGB v4 on Sharp Twin Famicom - LED 0 = S

[djanice1980]

Here's an interesting issue I’m experiencing with my Twin Famicom.

I seem to be running into the same type of “reset bug” that others have reported, where the NESRGB sometimes doesn’t initialize properly. In these cases, audio works fine but the screen stays blank. On my system when this happens, the LED indicator lights up in the 0 position, with no other lights showing.

If I manually select a palette, everything works and the screen comes up normally.

A few extra details:

This problem only happens in cartridge mode — it never occurs when using the disk mode (which is an odd quirk).

I’ve read on various forums that people fix similar issues on front loaders by replacing capacitor C8. Obviously, this is not a front loader, but I’m wondering if I should try replacing the 0.47 µF capacitor near the reset switch.

The reason I think it "might" help is because of this blurb from Tim:

"The design of NESRGB version 4, which uses a RAM based FPGA and a helper microcontroller to read the controls, requires a bit of extra time to start up when the console is switched on. The power on reset delay of the front loading NES is too short so its timing capacitor must be changed to accommodate this. Start up delay on the Famicom consoles is normally fine as it is, but a replacement timing capacitor is included with the kit just in case it has failed. The NESRGB can detect if the timing delay is incorrect and will blink LED 7 at power up if this is the case. A fast blink means the timing capacitor must be replaced. A slow blink means it is marginal."

https://etim.net.au/nesrgb/NESRGB40.html

My kit for the Twin Famicom did not contain a capacitor.


Another potential fix I’ve seen mentioned is cutting the reset pin on the NESRGB board assembly. As seen here:

viewtopic.p ... 4&start=60



My questions:

What can I do to fix this? Is this issue related to the reset timing? Should I just wire the palette to an old school reliable toggle switch?

Any advice would be appreciated! Thanks in advance.