[SOLVED] Sega ST-V Bright/Intermittent Display and more.

[SpoonyBard]

I recently picked up a Sega ST-V board. I've got Die Hard Arcade and Shienryu for it, and both are displaying very bright and the picture drops out in certain spots on each game (and it happens quite frequently). I bought the games from different sellers and from what I can tell, they don't appear to be boots.

I have it hooked up through my supergun which uses a Neobitz S-Video encoder and an arcade power supply (+5v 15a, +12v 2a, 110w). It's done this through S-Video and Composite on four different TVs (three CRT, one HDTV).

If any audio is hooked up, I also get interference to the point where the screen is entirely distorted. Audio is set to the absolute lowest it can go on the board, in the game and on the TV. This problem goes away if I unplug the audio cable from the TV, so this isn't a big issue for me.


I know that the ST-V has a problem with the +5v, so I raised it a bit and couldn't remedy these problems on any voltage I tried. The Supergun displays my MVS and other Jamma boards just fine. The sound interference is present on my MVS board, but it's very negligible. It's not at all present on the other boards i've tried.

Any ideas? There doesn't seem to be a whole lot of information out there on this board.


TLDR: My ST-V is displaying a very bright picture that shuts off intermittently. I've tried raising the +5v with no success. All equipment but the board and carts are known to be working.

Solution: Wired in 1k Ohm trim potentiometers on each of the Red, Green and Blue lines before they reached the encoder. Brought them up until the color appeared as it should and that solved the intermittent display issue.

Connected RCA jacks to CN24 (stereo/line-out. Pinout: L+,L-,R-,R+) and used those instead of the audio off the jamma edge. This stopped the audio from distorting the video and allowed both to play simultaneously without problems.

[Hobie-wan]

Ground problem perhaps?

[SpoonyBard]

I'm going to bring my test equipment home tonight and see if I can find a bad ground then. Thanks for the reply! I'll post some results tonight.

[Hobie-wan]

I don't know, that was just a suggestion since maybe it is using a common ground and once the audio is connecting to the ground things go to hell. Maybe someone else will have a better idea.

[SpoonyBard]

I'm all for suggestions. There's next to nothing out there on this board and the service manual offers no help for these problems.


Thinking back, I actually moved the audio ground to its own pin on the harness with the same result. I also added 11k ohms resistance to the output to bring it down to line level at the same time.

[mjmjr25]

That it's playing before dropping out should rule out any issues w/region or any bios upgrades.

There are 2 switches on the motherboard right next to the expansion slot - the first switch is your test mode, the second switch goes through the options. You should be able to run tests on the mobo and determine if it's mobo or cart related. If neither of those, then it's the TV (unlikely if running at 15khz) or supergun.

Problems with these boards are almost always from home repairs and bios mods. Most commonly the SH-2 processor chips. Give those a good looksee to confirm no wonky soldering...

[SpoonyBard]

I should have mentioned that I did run tests on the motherboard and carts. The only fail was on the motherboard battery. It's a US Bios and an unmodified board (at least to my knowledge, there's no visible repairs/alterations).

I've had the same problem with multiple TV's. The board and my main TV are both 15khz. Maybe it just doesn't like the encoder.

I'll check out that processor tonight as well.

[SpoonyBard]

Both SH2 chips seemed to check out. Tried pressing on them while running the game and no change. Pressed each chip and nothing on those. Ran self tests again with no change.

I did notice an added 100ohm resistor from IC18 (dual differential line driver?) to CN18 (serial communication connector) though. Pressing on that caused the picture to go blank. No change in brightness. How I didn't notice this the first time, I have no idea.

There was also a glob of solder bridging pins 7 & 8 on IC19 (digital multiplexer). It was on the component side of the board, so i'm assuming it was either a repair or the aftermath of a bad repair.

Removed the resistor from IC18 to CN18, removed the solder bridge between pins 7&8 on IC19, cleaned the cartridge connector once again and replaced the CR2032 battery. Once I get home i'll fire it up and see if i've made any progress or set myself further behind.

[SpoonyBard]

No change... Self tests still check out fine.


Does anyone have an ST-V that they can maybe take some board pics of? Seems every one I find is incredibly small, and i've yet to find a picture of the solder side.

[SpoonyBard]

Set up some 1k trim pots on the red, green and blue lines before it hit the video encoder. Adjusting them allowed me to dial in the right amount of color and after testing Die Hard Arcade, that also seemed to fix the screen dropping out. (Adjusting the color on the TV did not work)

After doing some reading, this appears to be a compatibility problem with the Neobitz S-Video encoder. Allegedly the Jrok encoder (or possibly the Neobitz component encoder) is better for this board, but with a few dollars worth of parts and a quick solder job, it can work just fine.

Audio still cannot be hooked up to the TV. Instead of distorting the picture it now drops the signal entirely. I'm not sure if that change came from removing the resistor a few days ago or from fixing the picture. I'm going to try and hook it up to an external source tomorrow and see if that works. Maybe i'll just add a speaker to the supergun.

*Edit: I'm just going to keep editing this with things i've tried until I actually come up with something significant.*

9/26 - Audio still doesn't work. When connected to the TV, it drops the video signal and you can only hear the audio coming through. If the audio cable is disconnected from either the television or the supergun, this problem stops. Setting the volume pot to 0 on the board does not though.

Tried connecting the audio straight to a receiver and outputting through a pair of home stereo speakers only to have the same thing happen. Noticed slight distortion to the screen (otherwise showing no signal) during peaks in audio and decided to raise the volume level on the board. When increased, picture slowly returned to the screen, albeit slowly; still distorted; and never completely returned. All of that even though audio wasn't even connected to the same device.

Since reducing the volume to 0 on the board (and leaving it at 1 in the BIOS and as low as possible on the receiver) didn't stop the problem, i'm assuming that adding no amount of resistance to the line would help. So i'm going to go back in and check the grounds. Maybe remove the video ground from the harness altogether?