Model 1 VDP2 issue

[griffin22]

Hi guys, new to the Saturn and have had a model 2 for a few months. Always liked the look of the model 1 and read the model 1 suffers less of the wobble my model 2 shows so thought I would get a faulty one to fix up. I got it with a known image issue where it puts a lot of garbled noise on the screen, but some 2d elements look fine. The 3d models in Sega rally are OK on the car selection screen but the actually gameplay is just garbled mess apart from the speedo and time. That led me towards VDP2 and on inspection of the chip pin 115 shows a blackened mark on the top so I think that chip has failed. I'll be recapping the whole board next week anyway, but was wondering if it was possible to get a replacement VDP2 chip from anywhere?

Cheers,

Alex

[griffin22]

Hi guys,

Just a quick update on my model 1 with a suspect VDP2 chip. I managed to complete the full board recap (and that was much harder than I had anticipated I will be honest) and fired the board up. Unfortunately it still shows the exact same mess on screen as before, but the game still seems to run OK fro what I can see of it. So it looks like the chip is fried. I'll try reflowong the memory and VDP chips as a last ditch effort, but I was wondering if anyone knew if replacement VDP2 chips could be found at all or if the board is now scrap.

Cheers,

Alex

[griffin22]

Hi guys,

Another update on my model 1 with graphics issues. I finally managed to procure a faulty board to use as a donor for VDP2. Having swapped VDP2 I had the same graphical issues (vertical stripes on the menu screen and 2d parts of games as a garbled mess).i then swapped the VDP2 ram as well just in case it was that causing the issue, and still the same. I played robot pit on it and it's pretty much perfect, but Sega rally is a complete unplayable mess so I am a bit confused as I was sure it would be caused by VDP2. I am planning to whip the chips back off and check all the traces are in good order (should have done that first really) but before I do if anyone has any ideas of what else it might possibly be that I could check first that would really help. It might be the replacement chips I used are also faulty, but given its exactly the same issue I think that's less likely.
Any help would be very much appreciated as this one has got me stumped.

Cheers,

Alex

[griffin22]

Sorry, that was meant to say robopit

[zyrobs]

some pictures would be helpful.

[griffin22]

Hi,

I have reassembled the Saturn fully now and tested all my games to see what does what. It was actually quite surprising how it behaved and I have got a large selection of pictures detailing it all, but in summary it looks to be the following:
All fmvs play perfectly, but with a strange and glitchy boarder
Black screens tend to have a pinkish hue to them
Vertical striping is a very common them across all games, but some have additional graphical errors
Robopit looks near perfect in gameplay
Daytona just has blue vertical lines
Discworld was surprisingly clean with just vertical lines
Virtua fighter 2 also just has brown vertical lines
Virtua fighter 1 and Sega rally are completely unplayable due to the amount of noise on the screen
Wing arms is pretty OK but with black striping
The Sega logo and text is always messed up
The text in the action replay menu is also jumbled up.


Below is the link to the folder I created for all the pictures, there are quite a few:

photos.app.goo.gl/p6xPW4WrZjWcUQ728

If you can't access it I can grab a select few and try to get them directly in this chat.

I am guessing it is a memory issue now having seen how it responds with all my games, but I jist need to figure out what is used more by VF1 and Sega Rally and not VF2 and the other games. Its rather odd and very interesting.

[zyrobs]

I meant pictures of the board, haha.
But yeah, that does look like the VDP2 can't read part of the VRAM right. Have you tried doing a continuity test between the VRAM pins and the VDP2? Since you mentioned pin 115, I'd focus on IC15 first. You said you completely changed all the relevant VDP2 components (the VDP2 and both VRAM chips), so I'd guess there's a continuity problem on the motherboard.

[griffin22]

Sorry, it was mostly back together after testing last night so I just finished buttoning it up and tested all my games this morning.
I have checked a few of them, pin 115 was checked first, a handful of address and data lines on both ram chips, but it's not easy to do so I think my next step is to take all 3 chips back off and test the traces without anything on. That should be a lot easier, and now there isn't any glue on the ram chips they will be a heck of a lot easier to remove.
When I get it stripped back down I will get some more pictures pre and post removal.
Thanks for the help and I will keep you posted with what I find. I'll probably be back with more questions soon

[griffin22]

I got around to removing the VDP2 again, and figured I'd have a quick poke around before taking the RAM back off. Completely forgot to get a picture beforehand but I think I might have just found the problem. It would appear that pin 124 is not making a connection to the via. I can't quite tell exactly where the break is but I am guessing it is near the pad, and since it is address line 3 for IC15 I think it makes sense. How it happened I don't know, and also how I repair it is currently a bit of a mystery to me. But I am very happy to have found a likely candidate. I have only checked about 70% of the pins so far so there might still be more, but I'm hoping not.

I tried to get a few pictures and put them in the album linked above, but my camera doesn't like close up stuff much so they aren't great.

[zyrobs]

Yeah that definitely looks like the problem. You can even see a bit of scorching on the trace going to pin 124, like it dissolved somehow. And the video problems you are getting would match the issue as well.

I'd try to solder some tin on the trace. There might be enough copper there that you can "reinforce" the trace this way, and get a stable continuity.
Failing that, I'd put some thin single strand wire through the via and soldered in place, something like 28AWG or thinner, that could bend 90 degrees and fit under the VDP2. Make it long enough to reach out under the corner of the chip, then loop it back and connect it to the pin/pad after you put the chip back.

That looks like an excellent desolder job by the way.

[griffin22]

Thank you for the compliment on my desoldering, it's certainly improving thanks to this board!

I will buzz out the rest of the pins and hope that this is the only issue, hopefully there isn't any issue under the ram too.

I had a go at thinning it up after gently scraping the solder mask with a scalpel tip, but the gap in the trace was actually from the pad to the first bend so it was too far to bridge. Looks like it's a wire repair. I have ordered some thinner wire as my usual mod wire is too thick to go under the VDP2, so in a few days I'll get back to it.

Keeps your fingers crossed I can bring her back to life, I'll keep you posted and thanks for all the help guys!

[griffin22]

Hi guys,

I finally got around to attempting this repair. Having finished buzzing out all the other VDP2 pins it was only the 1 bad trace that seemed to be the fault. I ran my 0.1mm wire from the via and out the side of the chip and after a little bit of fiddly soldering and a slightly less than desirable routing of the wire to the pad I managed to get something I was halfway happy with. And......

It works! I honestly can't believe it. I'm so happy. I threw a few new pics into the link above to show the fix and the result. Only tested with Sega rally so far, but given how unplayable that was originally and now it is perfect I think I can call it a success.

Thank you guys for all the help with this. I'm looking forward to so wobble free gaming very soon.

[zyrobs]

Glad you got it sorted out!

[davyk]

Splendid!!!

Another Saturn kept alive.