Snow bros bootleg graphics fix

[Lurch666]

So I got a faulty snow bros bootleg from philmurr that worked with sound but....

At first the screen was flickering as well like there was a sync problem.

After checking the sync and getting nowhere I decided to try with the video probe.

What I found was some of the missing graphics data appearing at the two LS374s circled in this picture.

So I checked them with the slice and found a faulty one which I replaced.

This didn't fix the graphics but it did stop the flickering so i got a steady picture.

Guessing I was on the correct track I managed to follow the trace for one of the pins with the missing data on it to this LS158 near the CPU.

Again slice told me it was faulty and replacing this one fixed the graphics completely.

Now the game is fully working.

It's a very specific problem but since there's no schematics for this board hopefully it can help someone with the same problem.

 

[Flinnster]

Ah I didn't realise there were no schematics for this pcb. I have one that boots to either ROM ERROR or RAM ERROR wording. Not had a chance to look at it much.

 

[jonhughes]

Great fix for a great game. I’m just doing the HS save mod on one of mine.

 

[Vamino]

Pretty sure I've got a boot of this in one of my boxes.

That slice gizmo sounds useful. Do you find yourself using more often that your other stuff?

 

[Lurch666]

Slice is just another tool in your arsenal since you need to know where a fault might be.

The star of this show was my video probe since there are no schematics to follow it helped me to find where the data for the graphics were being lost.

But once you find where the fault might be you can test a 74LS in circuit with the slice that you think might be bad to see if it needs replacing.

I'm not yet using the slice fully as it takes some time for someone like me to fully utilise the information it's giving me but that's true of a lot of the things I use to help me fix PCBs but it's proving useful saving me replacing ICs that don't need replacing.

Lurch6662020-11-03 22:04:20

 

[Purity]

The board looks like it has bad corrosion?

 

[Lurch666]

It's just the patina that you sometimes get on old PCBs.

The tracks are good as far as I can see.