Dreamcast Slow w/ Distorted Graphics

I recently purchased a broken Japanese VA0 Dreamcast that when powered on, will boot extremely slow and outputs distorted graphics (see video below). The Dreamcast does seem to work otherwise and will boot games. I've narrowed down the issue to the motherboard by swapping out the power supply, GD-ROM, and controller board with known working parts. I'm not sure where to start in troubleshooting the motherboard though. I've searched online and found a few people that had similar problems but none really provided a solution. One mentioned replacing some caps fixed the issue but they didn't specify which ones. Any ideas would be appreciated!



Update: I tested all the caps on the motherboard with a multimeter and 9v battery (connected in series). They all seemed fine except for the one labeled "CE301" which is a few caps to the left of the A/V port. It doesn't charge to the full 9v (only about 6-7v) and decreases from there. I checked a couple other motherboards and this cap should keep a steady 9v. This could be the culprit. Does anyone know what the proper replacement for this would be? I tried a 10uf 50v ceramic but that didn't seem to work.

 

If you are connecting a 9v battery to the caps while they are on the circuit board, you will probably damage the other components on the circuit board. You also can't properly test caps like that anyway

 

Hmmm good to know. I just found that method on some old forum post. It doesn't seem to have caused any damage. It still boots up exactly the same. Regardless, I still think that cap is at fault. There's obviously something wrong with it since it has different readings than in the other motherboards I have. I just need to know what the proper replacement for it would be since the ceramic I tried didn't seem to work.

 

this is just speculation, but i've seen a video where somebody progressively destroys the bios code and the result looks similar to your video. could be corrupt bios

graphics cards also behave similarly when they're about to kick the bucket. maybe GPU or CPU need a reballing

but again i'm just speculating

 

I just tried swapping out the BIOS chip but no luck. Displays the same symptoms as before. :-(

 

This problem has popped up before but a solution was never found.

The cap u referred to is related to the sound processing according to the known schematics, it may be different for your revision. It is a 10uF 6.3V electrolytic cap but it probably isn't the cause of your symptoms.

The symptoms are more likely related to the PLL chip (IC305) which handles the clock frequencies which would explain the slow cpu and graphics glitches. I would first look at your psu and make sure the voltages are clean. U will need an oscilloscope, a DMM won't give u a complete picture. If the psu is good then I would look at the PLL chip or caps related to it (CE307 22uF 10V).

 

I've already swapped out the PSU with a known working one and it didn't make any difference so that's ruled out.

Interesting. I should be able to swap out that chip with one from another mobo. I'll give that a try tomorrow. Thanks!

 

I had a similar issue where all the menus were green squares and the Dreamcast logo didn't display and neither did the games at all. I tried to swap over capacitors from a different dead board out of boredom but it didn't fix anything and I threw it away. Probably due to the GPU dying, looking at yours it doesn't seem too much like the same issue so I can't say if that'll help or not. But there are issues like this happening nowadays in general.

 

I have a PAL VA1 board with pretty much exactly the same issue, so it's not a one-off problem.
Unfortunately I didn't put any time into it myself because I needed all the other parts for a different Dreamcast, but best of luck for finding a solution!

 

Well I was going to swap out the IC305 with one from another motherboard but I don't have another VA0 (not one that I'm willing to salvage parts from anyway) and it looks like they changed that chip with the VA1 and VA2. It's not even the same size (it's 1mm wider). Unless anyone has another idea, I guess this repair will have to wait.

Edit: I decided to take a risk and use the chip from a VA2 motherboard. The pins still line up even though the VA2 chip is a bit smaller. The good news is that it works. The bad news is that it still has the same symptoms as before. Looks like the IC305 isn't the issue.

 

It might be worth recapping all the electrolytic caps on the motherboard. I read another thread where this fixed that person's slow boot problem but it didn't specify which cap was the culprit. Good luck.

 

Yeah I'll probably try that at some point. I don't think I have all the caps I need right now. Does it matter if I replace them with ceramic caps? As far as I'm aware, they should work fine as long as the values are the same (or higher in the case of the voltage).

 

Here is my thread (which you have probably already seen), showing my Dreamcast VA1 board with similar issues.
https://assemblergames.com/threads/slow-dreamcast.69090/
I swapped over the clock chip and crystals for known working ones but it made no difference, I didn't replace any of the capacitors though.