How To Get Williams PCBs To Work With LCD Monitor

RetroCJT

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Hi all. I built a rudimentary test bench at work to test/fix boards at work while I have downtime. Unfortunately all I have available (and all I have space for) are VGA LCD monitors here at work to use for testing. I have tested a few boards and they have all displayed a stable picture and worked fine. That is until I tried my Stargate. It is 1-3-1 erroring, so I want to take a look at the rug pattern, but even with the positive sync trace cut, it still will not sync to the monitor. I am using a Gonbes GBS-8200 for video conversion, and it looks like it is trying hard to get a picture to display (cutting in and out and trying different refresh rates or something) but it will not display a stable picture. I can see the rug pattern occasionally for a brief moment, but it is not synced and then it just goes black with "NO SIGNAL" displayed. Anyone have any luck with using LCDs in Williams games? If so I could really use some help! Thanks!
 
I announced my retirement the other day. on a serious note I didn't have issues with running them on an arcade grade LCD. maybe it's a problem with the positive sync?
Hooray! He lives. Thanks man didn't mean to pester ya. Hmm, very interesting. I have had no trouble testing Williams boards on a CRT. This is the first time I've ever tried it on LCD. The GBS-8200 has only a single sync wire. I know before with Williams games I have used the two separate wires in the cabinet, but on the test bench with a CRT the single one generally works ok. Who knows. Maybe the move is test it on the CRT to determine if it's a problem with the GBS?
 
I announced my retirement the other day. on a serious note I didn't have issues with running them on an arcade grade LCD. maybe it's a problem with the positive sync?
Now I will say this is just a 4:3 VGA monitor, idk what qualifies arcade grade.
 
i'm no expert, please report back

from what i understand, you can take a csync signal from a pcb to a monitors hsync and vsync inputs, but combining the two separate outputs to create a csync signal is different and needs some circuitry

please correct me if i'm wrong
 
i'm no expert, please report back

from what i understand, you can take a csync signal from a pcb to a monitors hsync and vsync inputs, but combining the two separate outputs to create a csync signal is different and needs some circuitry

please correct me if i'm wrong
I will test it tomorrow morning and let your know. Thanks very much!
 
i'm no expert, please report back

from what i understand, you can take a csync signal from a pcb to a monitors hsync and vsync inputs, but combining the two separate outputs to create a csync signal is different and needs some circuitry

please correct me if i'm wrong
I see people suggesting combining H+V and I don't think it works that way

try pin 7 = csync
also by that point when I turned my Williams harnesses into a JAMMA adapter I started using the secret positive composite sync pin lol

Now I will say this is just a 4:3 VGA monitor, idk what qualifies arcade grade.
like Wells-Gardner, Happ, or Makvision. not a computer or TV LCD
 
Interesting. It is labeled as no connection on the Stargate drawing set. I had no idea. Thanks!
It's labeled in the schematics:

Leave W1 -- cut and lift pin 5 on 4A and jumper it to +5V.

Then you have positive separate sync for the original harness and negative composite on pin 7 for JAMMA.

1757678170800.png
 
It's labeled in the schematics:

Leave W1 -- cut and lift pin 5 on 4A and jumper it to +5V.

Then you have positive separate sync for the original harness and negative composite on pin 7 for JAMMA.

View attachment 846295
that's still positive sync. there is a jumper you can change to make it negative sync though I've never done it, because I wasn't going to change it on a bunch of boards. I just added the inversion into my JAMMA adapter.
 
It's labeled in the schematics:

Leave W1 -- cut and lift pin 5 on 4A and jumper it to +5V.

Then you have positive separate sync for the original harness and negative composite on pin 7 for JAMMA.

View attachment 846295
I see people suggesting combining H+V and I don't think it works that way


also by that point when I turned my Williams harnesses into a JAMMA adapter I started using the secret positive composite sync pin lol


like Wells-Gardner, Happ, or Makvision. not a computer or TV LCD
Okay so I tried everything with no dice. I finally brought my logic analyzer up to work and stuck the logic clip on the 7486 sync chip. I think it is toast. I brought another MPU up to work, cleaned it up, cut W1 and tried it, and immediately, beautiful rug pattern with no sync issue. Oddly enough, the game booted just fine with this MPU (which I had actually brought for parts to fix the other one lol) after some RAM swapping. So evidently, it is the MPU. I don't believe a bad 7486 would cause a 1-3-1 but i have checked the multiplexers and some other troublemakers and the logic all seems to check out on those. Thanks for all the help guys. I have got a working Stargate board set for now which is what I was after. I do still want to fix the other MPU so any ideas on where to start with it are always appreciated. Thanks!

To summarize, there is nothing wrong with the monitor or GBS-8200. It is a board issue, but I have yet to find out what is the cause.
 
with the working board was it wired with pin 7 or combining h&v as you originally had it? i don't think the latter would work but always like to learn
 
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