Sega ST-V -- stone dead

roothorick

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So my ST-V board arrived... and it's stone dead. The LED on the board comes on, but I get nothing onscreen and no audio. The onboard battery was low (1.5v) so I swapped it with one out of a computer that I tested first (3.03v)... no change.

The first run, I unknowingly had the voltages pretty high. +5V was over 6, -5V was about -5.98, +12V was above 14 I think. The other two boards I have (Gunbird and Lucky n Wild) didn't seem to mind the raised voltages at all -- in fact since Gunbird was working I kinda assumed.... I really wish I had checked now. I don't know for sure if that's what killed it, but... lesson learned.

My instincts say I should verify the BIOS ROM, but I have no idea how to do that. Even if I had a reader/burner, it has a hacked universal BIOS, so I don't have a ROM to compare it against.

I thought tomorrow I'd borrow the logic probe from work and check for signs of life around the board. I'm not sure what else to try.
 
Progress! After reading some things online I tried turning it on while holding SW1 on the board. I got this:

IMG_20110804_185013.jpg


That's incredible news. It means, at a minimum, master CPU, at least one VDP, video output, and at least part of the BIOS EEPROM is good. Which begs the question, why do I get a black screen on a normal boot?

It's running the continuous test now. We'll see what happens.
 
It boots!.... but there's sprite problems. And it periodically crashes. I think one (or both) of the VDPs got toasted from the overvoltage :(

It's almost always different sprites/textures that are goofing up, but they all goof up in the same way (warped off to the left of the screen), which tells me 99% chance the cart is perfectly fine. I'm not sure if I'd rather have a bad board or a bad cart...

You know, I'm gonna go through ALL the tests. Who knows. Also, I have a lead on a second ST-V board, so even if it's a blown custom IC and I can't find a Saturn to cannibalise, hope is not lost.

-E- I forgot to mention... sound is there, but EXTREMELY quiet. Like, barely audible in a quiet room, quiet, and there's a staticy buzz over the top of it. Oh, and it sometimes fails to boot (black screen) and makes loud static noises.

This is gonna take a while :( I'm just gonna pick up that second STV.

-E2- All sound tests utterly fail. Both "SOUND RAM" and "MIDI COMMUNICATION" come back "BAD". I should also mention, I'm getting no sound at all.

-E3- Damnit, I need a KG for reference. Wow, what a way to begin my soak box.
 
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Putting my thoughts down so I remember when I procure the new ST-V board.

I'm fairly certain at this point I'm looking at multiple failures, probably caused by my miscalibrated power supply. Current hypotheses:
  • Master CPU reset goes high before it's supposed to, causing intermittent booting
  • VDP2 VRAM issue causing sprite corruption, this may also be the cause of the freezing. It's worth noting there are NO glitches on 3D objects.
  • YMF292 is basically dead. Audio amp probably OK.

Of course, I can't confirm any of this just yet. Once I have a logic probe and a known good board, I'll start really cracking down.
 
Man, nobody is giving you any love on this thread - some serious troubleshooting happening here..Good work. :)
 
Run the Dual CPU test.

The biggest problem with ST-V boards is that people flex them and pop the solder joints on those 2 CPU chips with the hair thin legs.

You most likely need both of them resoldered.

RJ
 
Run the Dual CPU test.

The biggest problem with ST-V boards is that people flex them and pop the solder joints on those 2 CPU chips with the hair thin legs.

You most likely need both of them resoldered.

RJ

I read about that -- I tried the test, it consistently comes back good, if the machine doesn't freeze first. It would line up with the freezing if just one pin -- reset -- was making intermittent contact. That cannot explain the cataclysmic sound failure though.

Tomorrow I'll play with flexing the board and pushing on the CPUs, and see if I can get it to freeze or reset just by flexing it a certain way. Who knows. I'm half-tempted to just bake the whole board in an oven.
 
With the legs OFF of the board, push down on each CPU (so you aren't flexing the board)... OR if you have the legs on, pinch each CPU and board between your fingers when you run those tests.

I'm thinking the lockups are the main CPU needing reflowing. It could explain the sound issues too, if the address lines needed aren't making good connections.
 
For the people with their own problematic ST-V boards, who are smacking the search button: The board will boot, somewhat, without a cart. A healthy board missing a cart will give an "ERROR ON CARTRIDGE" message you can bypass by pressing SW2 or Service, whereupon it'll cycle through the copyright notice / patents / "SYSTEM CHECKING" and finally come up with a fancy ST-V logo screen complete with audio. So, you CAN test these boards without a cart. I'm certainly gonna leave my one and only very expensive cartridge sitting in the box until I have a ST-V board that at least passes that much test.
 
I have some st-v pcbs I pulled out of a print club. They won't work with usa carts, but I think thats beacuse they need the terminator pcb. They have a s-video interface board plugged into it.

It could be that they don't work becasue they want japanese carts. I can test the terminator theory as I have a working stv pcb. If its correct, youhave all the parts you need to make my board work with your cart..
 
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