K4901 on Joust

andyrew

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Hi, all.
Still having trouble with a joust machine. It's got a k4901 in it that has been recapped and it's having rolling issues and picture skew/twist. I can't figure out what is causing it and i haven't been able to find any threads with similar issues.

The game looks like it was converted to a composite sync at some point as the sync wires from the game board are twisted together in a weird combination, and the sync wires are jumped at the chassis.

When I power it up, it rolls for a bit and will eventually stop, but usually I have to give the hold a little jiggle first. Once that stops the picture will be centered correctly at the bottom but it slants as it goes up until about 6" are off the screen to one side or another.

Would this be a sync issue still or could it be another problem? I have worn myself out trying to figure out this issue. Attached is a picture of the 'tilt'.

Again, the board was recapped, the solder joints all look good and the polarity all looks right.
 

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Actually, its hard to say with hacked up wiring, I'd fix up the wiring however it should be originally. I'd test it on a known good monitor then.
 
you can't simply twist the sync wires together and make it composite. if that were the case people would've done that a long time ago instead of tapping unused pins (pin 7, where the key is) and creating signal inverters to work with JAMMA.

from the video header on the MPU, the wires should be as follows with the original wire colors:
pin/function/wire color
1. red: violet-red
2. green: violet-green
3. blue: violet-blue
4. video ground: black
5. positive vertical sync: violet
6. positive horizontal sync: violet-white

separate the sync wires and connect them properly to the monitor on the positive sync pins (the block of 6 pins, not the separate 3 pins)
 
Sorry, I should have added that the machine was working fine before the power supply rebuild/recap monitor. The chassis was already converted to a composite sync and worked correctly. The wires were disconnected and I tried many combinations until I got the picture to look like it does. So I believe it's either a sync problem or something in my recap job. I just don't know where/how to check which.
Is there a specific area on the chassis that I can double check that would be causing this problem? Is it possible i still have the sync wires in the wrong combination that will get this close but not perfect?
 
you say it's modified for composite sync, but then you said that the horizontal and vertical sync wires were connected together. that's not composite sync, that's horizontal and vertical sync combined together. barring whatever this mod is that you're referring to, it's completely unnecessary. it's not like if you connect an H+V game like Stargate with a composite sync signal that it's going to be high definition.

I implied in my last post that you should simply undo that wiring arrangement and just run it as H+V, as the game was designed and intended.

a rolling or skewed picture is symptomatic of vertical sync not connected where it needs to be, as you have stated. that's because your video signal isn't feeding the vertical sync information to the monitor at the position where it needs that information. which makes me wonder what your composite sync mod is.

if you insist that the game worked right before you capped the monitor then I would venture you probably either installed a cap wrong (backwards, wrong rating, etc.) or you set a solder bridge between 2 points that shouldn't be connected. pull the chassis back out and thoroughly look it over to verify this.

I'm curious as to how you rebuilt the power supply as well. there's about 57 ways it can be done and what people call "rebuilding", and only one of them is right.
 
I've tried that before and it doesn't work. I've also tried it on another chassis and it doesn't work. So the chassis I'm working with has been modified somehow to take a composite sync.

I looked again and the purple/wh to the chassis is jumped with the purple so both sync lines are taking the same signal. When i powered it on today it wouldn't stop rolling so i guess i didn't have the syncs tied in together the way i thought. I think i had it so the bl/pw from the game went to the bl of the chassis, and the p from game when the pw of chassis.

Are there jumpers or something else on the chassis that tells it to accept a composite signal? if i can find what it is i will try to undo it to see if i can get straight signals to work again. but as of now i can't get this game back up and running again.
 
do you know why it's rolling?

it's because you don't have vertical sync connected. I outlined exactly what was needed to be done. I even provided the exact pinout of the video signal.

because Joust is not a composite sync game, it's H+V, it has separate sync signals for horizontal and vertical syncs. I already outlined that you can't just splice wires together and feed them to a single pin. if your video harness is just missing the violet vertical sync wire entirely, I will make you a new one.
 
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