PCE GT - Help diagnosing problem

[MasterofBiscuits]

I recapped a GT today that was totally dead. Did all the caps, cleaned it up and gave it a test and it was all working great, good picture and loud sound. Then I decided to wire up the RGB outputs to the HUC6260 and do the jailbar caps in preparation for a screen mod tomorrow. After doing this and testing again I got a blank screen and no sound. I checked my work again and I noticed I'd put one of the caps in with the wrong polarity - CC504. I replaced it but still no joy. I then checked all the RGB wiring and it was fine but I removed it anyway and still nothing.

The backlight is definitely working as I can still see a stuck pixel on the screen, this is a lack of video & sound. I'm beginning to think the reversed cap may have fried one of the ICs, and will probably try swapping them tomorrow - anyone have any other ideas on what this could be? I've tested for shorts all around that side of the board and haven't found any.

[bdoi]

Do you have any pics of your board?

[MasterofBiscuits]

Sure, see here: https://imgur.com/a/mVuxw83

I've tried a different screen and also tried running the RGB output direct to the screen on another RGB-modded GT I have and there's no picture, and no sound, so it definitely isn't running the game. I've cleaned the cart slot and tried several carts. Voltages I've measured around the board seem correct.

Edit: replaced most of the caps today with ceramic/ tantalum just because it's quick and still same issue. I'm pretty stumped at the moment, leaning towards it being a logic problem.

[MasterofBiscuits]

Slight progress; I swapped the HUC6280 in the GT with a white PC Engine I have lying around here, and it works fine in that console. The GT is still showing the same symptoms, but at least I've ruled that out.

[Keith Courage]

Might be random but did you check if any of the pins are bent in the card slot?

[MasterofBiscuits]

Might be random but did you check if any of the pins are bent in the card slot?

Yes I gave the slot a good check, cleaned, examined with my scope and tested the pins, it all looked good.

Not sure if it's worth swapping out the 6260, I'm not sure if that would cause the game not to run at all? What do you think Keith?

[MasterofBiscuits]

HUC6260 also swapped over, worked fine in the white PCE, no change to the GT.

[Keith Courage]

Honestly I can't provide more help since I've been stumped at times with white screen boot up systems as well. In most cases it's been a bad HU6280 but not always.

[Keith Courage]

Does the screen show white or is it black/very dark green?

[MasterofBiscuits]

It's black, and if I turn the brigthness wheel right up it will go white. There is a dead pixel on the right of the screen that is clearly visible, so I'm certain the backlight is working.

It's got me stumped but unfortunately I've had covid for the past week or so and not had the energy to look at it.