Problem with RGB modded PC Engine IFU

[dougal]

Hi guys, I've recently got an RGB modded IFU (Interface Unit) for my PC Engine and its been giving me a little hassle.

First stereo sound was only working from one speaker but I fixed that myself as the LEFT channel wire was soldered to the left audio ground instead of the actual audio point. That was an easy fix.

The issue is to do with the actual picture. The problem only presents itself in certain games, most are fine. I will give two examples.

Ninja Ryukendu - Parts of the graphics flashing bright/dim/bright/dim etc..
Tatsujin - Part of graphics flashing bright/dim/bright/dim etc..

If I plug into the the other SCART socket on the TV (Sony Trinitron flat tube 29 inch) the display is extremely DIM and hardy visible despite that I know that BOTH RGB SCART sockets on the TV are fine as I use other consoles with RGB on both those sockets.

If I plug RCA cables from the IFU original composite ports into the composite of the TV (but remain using the RGB) then the problem goes away and it works perfectly (RGB) on one of the SCART sockets (not the other) with the games in question which leads me to believe it must be a grounding or sync issue with the RGB mod but i'm not sure.

I tried an LCD TV with RGB SCART and there was no issues. I also tried my Philips CM8833-II monitor using an RGB to SCART adapter and there were no issues either.

I have eliminated the PC Engine itself (not the IFU) as being the problem as I tried another PC Engine in the IFU and same problem. I also tried an RGB modded PC Engine (not IFU) and no problem either.

Here are some videos I took:

https://www.youtube.com/watch?v=PojRPfKrYs8

https://www.youtube.com/watch?v=TNqxr--b0tA

2nd Video look at the red parts of the building flashing after I unplug the RCA cable from the yellow socket on the IFU

 

[roy_bates]

have you looked at the blanking and switching signals?...a monitor doesnt use those that would explain why it isnt dark on a monitor

but,normally if those are wrong its permantly dark.
but the video is so short i cant really tell what you mean,or its a sync issue

 

[dougal]

Its not dark per-say, as you can see from the videos, certain games flicker either certain parts or the whole screen to slightly darker back to bright etc etc... I noticed this in 3 games.

I tried connecting it to the TV differently. TV SCART --> SCART switcher --->Another SCART switcher ---> IFU/PC Engine and 99% of the issues have disappeared. I have no idea why.

In the meantime Otakus (the french PC Engine store who make the mod and also mod them) said I could try de-soldering the yellow wire (inside the IFU) and wiring it up to the Yellow RCA plug.

have you looked at the blanking and switching signals?...a monitor doesnt use those that would explain why it isnt dark on a monitor

but,normally if those are wrong its permantly dark.
but the video is so short i cant really tell what you mean,or its a sync issue

 

[dougal]

I did as Otakus said. I disconnected the yellow wire (Sync?) which leads from the RGB DIN socket to the IFU main board from the board side and instead soldered it to the Yellow Composite output solder point and now it works perfectly.