Sega Model 1 Virtua Racing Tilemap error

[Tailsnic Retroworks]

Hi. I have tried today to repair a graphic board of a Virtua Racing game. The graphic error I have only affect the tilemaps, and the 3D section is perfect.

In the attached photos you can see the test screen and the error. The screen tells me IC69, IC70, IC71 and IC72 are bad (those ICs fully correspond to tilemap section in graphic board, not TGP board). Fully inspected the tilemap section: rams, PALs, ICs and even exchanged the 315-5292 custom.

I don't know where to look because I don't know this system. Any help would be welcome.

 

[Mrhide]

test screen shows 'em all good?

 

[Tailsnic Retroworks]

test screen shows 'em all good?

No. If you see, those 4 ICs are BAD in the test

EDIT: wrong photo, that's from other test when discarding the graphic board. Changed to the correct photo.

 

[Mrhide]

ah ! ... now you changed the image

ok if they are showing as bad, you said "Fully inspected the tilemap section: rams, PALs, ICs and even exchanged the 315-5292 custom"
Does that mean you changed these ic or confirmed them as good? IC69, IC70, IC71 and IC72?

 

[Tailsnic Retroworks]

ah ! ... now you changed the image

ok if they are showing as bad, you said "Fully inspected the tilemap section: rams, PALs, ICs and even exchanged the 315-5292 custom"
Does that mean you changed these ic or confirmed them as good? IC69, IC70, IC71 and IC72?

Yeah, with another Virtua Racing graphic board I have with 3D section completely gone. Those rams are very difficult to test, but if you have another board, you can socket them and test them. Tilemap section is good in that board

 

[andynumbers]

What chip do you have at IC5? 315-5422 or 315-5422A? If you don't have the A revision take your video board and throw it in the trash. The original 315-5422 is a ticking time bomb and there are no replacement chips available. This information comes from Ken@irepairsega. Steal a video board from a Virtua Fighter. These are almost always running the A revision.

 

[Tailsnic Retroworks]

What chip do you have at IC5? 315-5422 or 315-5422A? If you don't have the A revision take your video board and throw it in the trash. The original 315-5422 is a ticking time bomb and there are no replacement chips available. This information comes from Ken@irepairsega. Steal a video board from a Virtua Fighter. These are almost always running the A revision.

It has the 315-5422A custom

 

[andynumbers]

So it's worth repairing then. According to a thread on KLOV from Ken: the vertical lines usually means bad ram. So replace those chips with known good ones.

 

[Tailsnic Retroworks]

So it's worth repairing then. According to a thread on KLOV from Ken: the vertical lines usually means bad ram. So replace those chips with known good ones.

They are replaced and are good. All of the components of that marked section has been tested with another board, and the problem persists.

 

[andynumbers]

No idea then. Send it to Ken.

 

[Tailsnic Retroworks]

No idea then. Send it to Ken.

I don't know how to contact Ken. Can you help me about that?

EDIT: answered myself. He is in California and I'm from Spain. It's not worth it the costs for sending it. I'll search for more in Spain

 

[waiji]

If 315-5292 is also replaced and the tile map-related RAM is replaced correctly, but the same situation repeats,
test whether there is a short circuit in the pcb pattern connected to the RAM.
If there is a problem with the wiring connecting the 315-5292 and the RAM, such a screen is usually displayed.

 

[Tailsnic Retroworks]

If 315-5292 is also replaced and the tile map-related RAM is replaced correctly, but the same situation repeats,
test whether there is a short circuit in the pcb pattern connected to the RAM.
If there is a problem with the wiring connecting the 315-5292 and the RAM, such a screen is usually displayed.

Thanks. I'll give it a try. There must be a short circuit somewhere then.

The board has a repair for one pin of the PAL 315-5483 to one of the 3 x 74F273N. Those 74F273N also fully tested.

 

[Tailsnic Retroworks]

I have news. I have tested different combinations of connected rams:

- IC69 + IC70 only
- IC72 only
.....

Only I have archieved to make a GOOD test puttin a ram on IC70 alone.
Putting rams alone in other sockets results in BAD.

I think there's some problem in another zone of the board. There must be some components in charge for the tilemap section far away the section. I'm beggining to suspect for the PAL 315-5483, in charge of the graphic priorities.

The PAL is good because I have exchanged it with another board.

I want to add that putting only rams at IC69-IC70 and lefting IC71-IC72 empty, the game works as always.
Puttin rams at IC71-IC72 and lefting IC69-IC70 empty, practically nothing 2D is seen.
In the attached photos you can see the 2 main pair combinations. The IC71-IC72 banks aren't loaded

 

[Tailsnic Retroworks]

I have solved the situation by other way.

I have another 837-7894-01 graphic board, which has clipping on polygons, and has 315-5422 custom.
I have changed the custom for the working 315-5422A on the graphic board with tilemap error. Now I have one fully working Virtua Racing board at least.