Weird interference with 2600 games and LHE mod

[ApolloBoy]

I already posted this over on the Hardware board, but I would really like feedback on this so I figured I'd post about it here so it'll (hopefully) get more attention. Anyway, I've been encountering a strange interference problem when I play 2600 games on my modded 7800, which has the LHE board. It's mainly noticeable on dark-colored backgrounds (especially blue) and nothing I've tried has gotten rid of it. I've used shielded wire, shortened my wires (which on a side note, totally eliminated the need for the TIA9 switch) and even tried disconnecting the MARIA chroma, all for nothing.

 

This problem has been here ever since I modded my 7800; here's some pictures of the interference, featuring level 1-3 of Princess Rescue:

 

Edited October 8, 2013 by ApolloBoy

[ApolloBoy]

Anyone?

[ApolloBoy]

Alright, I just tried replacing the 100 uF cap on the mod board, the main filter cap on the system and I even added a 0.1 uF cap across 5V and ground on the 4050 on the mod board, and so far nothing. I'm still not sure what the issue is here...

[+iesposta]

My 7800 LHE mod in S-Video has just the faintest hint of that dark in the blue on Princess Rescue.

Sorry, I can't offer any help, but just to report that mine has a faint similarity.

I have the switch in also for cleaner 7800 by switching TIA, of course when in 2600 it just give a black & white picture.

The mod was in the last run serial number X 7800, but when I found out it would not play certain homebrew games like beef drop and scramble, I got an older serial number A1 model and switched it there, modding the X to composite with a transistor and 3 resistors.

If it is not a problem with the LHe board, it may just be because there are more than 6 revisions of the 7800. Just guessing.

[ApolloBoy]

I'm beginning to think that this is caused by the newer TIA that the 7800 uses, as I tried this on my composite modded 2600 Jr. and I could vaguely make out the same interference pattern.

[ApolloBoy]

Bringing back this thread as I recently bought a 1984 7800 and I'm thinking of transferring my LHE mod over to that system. For anyone that has an expansion port model (or heck, even one of the later Taiwan models) with an LHE mod, do you get this kind of interference?

Edited November 26, 2016 by ApolloBoy