I've been Coleco'd

[stephen_usher]

If the games use sprites then the RAM issue cold become a problem as the VDP will be using the video RAM contents for collision detection. Also, some systems use the VDP RAM for input stuff in round-about ways. Less likely on a console though.

Probably best just swap it all out.

[HigashiJun]

@rubber_jonnie

Almost there !

:cheer:

[rubber_jonnie]

If the games use sprites then the RAM issue cold become a problem as the VDP will be using the video RAM contents for collision detection. Also, some systems use the VDP RAM for input stuff in round-about ways. Less likely on a console though.

Probably best just swap it all out.

Yes, I can't see it all lasting.

I left it running for a few hours yesterday evening and when I got back to it having left it running just fine, there was bad graphics corruption again. I've not tried it yet today, but I expect it'll be in a similar state with another dead RAM chip or two.

At least all the RAM is socketed now so it's a quick job.

[rubber_jonnie]

@rubber_jonnie

Almost there !

:cheer:

Yes, tantalisingly close :)

[rubber_jonnie]

Well Hmmm :pullhair:

I replaced all the RAM and I still get on screen corruption, so I'm going to leave it for a while and see if it clears up like yesterday.

There was another dead 4116 in the picture, so they are slowly failing but I'm wondering if the TMS9928B is failing.

However, I have now found the schematics, and it's told me two things.

1. The RAM is used only by the VDP, there is no other logic involved as the program RAM is elsewhere. The carts are running fine but not displaying properly.
2. Point 1 means that the problem is either the VDP or the RAM.

So what's next? More head scratching an a look around for a VDP I think. I will likely order some more 4164s as I'm using some hacked 41256's and I've had issues with using them before and it could just be that.

[HigashiJun]

Ah, damn !

That was so close...

[rubber_jonnie]

Ah, damn !

That was so close...

You're not wrong...

At least the current problems are fairly clearly limited to the RAM and VDP.

[rubber_jonnie]

OK, so I found some more 4164s and whilst I still have a couple of 4116's at play, everything else is a hacked 4164.

I have tried moving the RAM around in the bank and nothing changes, and it looks like it is the sprites that are corrupt, so I'm thinking it's more likely to be the VDP :(

I have tried reflowing it and no change, and on the basis I don't have a spare FDP to hand I've decided that in the meantime I'll recap whilst I check what VDP is installed.

Unfortunately it has a heatsink glued to the top, so that may prove difficult. I'm assuming it is a PAL version which I think has a B suffix, so a TMS9928B rather than the TMS9928A but I'll see if I can get the heatsink off without doing any damage.

[rubber_jonnie]

OK, so the heatsink came off easier than expecting, and it's a TMS9929A. Time to have a look and see what I can find.


EDIT: I ordered some but ended up going via Ali Epress as all the ones on eBay were about £10 a piece and coming from China, so I decided to risk £10 on 5 from Ali Express...

I've got 8 4164's coming from Retroleum too, you can never have too many 4164's. The re-cap is also done too.

[stephen_usher]

What does the corruption look like? You(/we) may be able to determine which bit is being affected.