Konami Gradius II/Twin16 PCB video issue

[jepjepjep]

Hey guys,

I'm having an issue with a Konami Gradius II. There is a graphics issue that only seems to occur in the first stage, where the star field gets corrupted during gameplay. It happens pretty often, but the strange thing is that it seems to correct itself if I die and the stage gets reset.

Here is a video of the graphics corruption:

And here is a video showing the corruption getting corrected after a death:

Any idea what would cause this behavior, or any suggestions on how to fix it?

 

[xodaraP]

I'd be verifying ROMs to start with, it's possibly a RAM issue since it corrects when the playfield is reset (you die and restart)

Since it's only happening in the first stage that suggests a fault in the ROMs as if it was logic or RAM it would likely occur in other levels.

I can't be 100% sure, but that's where I'd start

 

[caius]

Hardware is pretty complex : two 68000s CPU on top board and a lot of customs on VIDEO board.I've repaired several of them.For first, if you can, try to swap a good boardset in order to narrow the fault but judging from it I'd say it should be located on bottom VIDEO board.I guess the board is full of Fuitsu TTL.Does you boardset come with the GFX 4Mbit MASK ROMs on video board or a daughter board that replace them?Anyway, it's fixable for sure.

P.S:
Is it a genuine or conversion board?

 

[Apocalypse]

I guess the board is full of Fuitsu TTL.Does you boardset come with the GFX 4Mbit MASK ROMs on video board or a daughter board that replace them?Anyway, it's fixable for sure.

P.S:
Is it a genuine or conversion board?

This (Fujitsu TTL, only Twin 16 I've seen were almost 100% Fujitsu populated regarding TTL).
Is it my former Devil World board?
If so then it has 4Mbit mask ROMs and it's been converted.

 

[xodaraP]

Surely if it's logic based you're going to see the fault on other levels or other places?

I guess since it's minor it could be getting missed

 

[caius]

Surely if it's logic based you're going to see the fault on other levels or other places?

Probably issue will pop up again in later levels.Board is fixable though with some time and patience.

 

[jepjepjep]

Yes, it’s a conversion from Dark Adventure but I don’t think this pcb was yours Apocalypse, I’ve had it for many years. It’s a two layer pcb, with EPROMs for graphics on the bottom layer.

There appear to be over 50 Fujitsu ttl chips on the bottom board.

 

[Apocalypse]

Yes, it’s a conversion from Dark Adventure but I don’t think this pcb was yours Apocalypse, I’ve had it for many years. It’s a two layer pcb, with EPROMs for graphics on the bottom layer.

There appear to be over 50 Fujitsu ttl chips on the bottom board.

Interesting, I thought you were trying to fix it for Derick2k who has a similar issue (my board was fully working before shipping so I tend to think those evil Fujitsu TTL are the culprits as it happened many times to me before, they just die of internal corrosion even if board isn't used/powered).