K4951 with bizarre colors (Gyruss)

DrCharles

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I powered up my Gyruss the other day and the monitor isn't right... the black background is yellow. The "GYRUSS" text isn't visible, and the "Please deposit coin..." is replaced by a green bar. :oops2: Among other weirdness. The game plays normally except for the bright yellow background.

First thing was to determine if it's the monitor or the board itself... I hooked up the 5" Samsung color monitor on my test rig to the game video output, and it looks perfectly normal. That was a relief.

But now I have to fix the have already ordered a recap kit since I don't think it's ever been done. What can cause yellow instead of black?K4951. I have already ordered a recap kit since I don't think it's ever been done. What can cause the black areas to appear yellow instead?? I have plenty of experience with electronics, especially digital and microprocessor, but haven't been inside very many CRT monitors... Thanks for any tips.
 
I recapped the chassis, put it back in and the picture was back to normal :)

So I unplugged the game, moved it (partway) back towards the corner in case I had to tweak some adjustments, turned it back on... and the color problem is there again!! :poop:

Here is a snapshot during attract mode. Could a problem with the degaussing circuit affect the colors this much? Any ideas please?
 

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Yes, but it's not a board problem. Please see my original post - when the video outputs are hooked up to a portable monitor, the display is perfect. So the problem has to be in the game monitor!

I've thought about it some more, and I think the trouble may be in the black level/blanking circuitry, which is fairly simple. When the game is playing, I can see red, green and blue colors of the ships, projectiles, asteroids and so on, and when the 500, 1000, etc. scores flash on the screen, they are white as intended. But I'm still not sure why the background is not gray or white instead of yellowish though.
 
the monitor, no matter how broken it is, will not generate solid colored boxes where the text is. when you're mucking with connecting it to your portable monitor you're probably moving a chip on the board enough to make the graphics cut in and out. my advice is to take the boards out of the cage and the quick and easy and maybe you get lucky solution is to press the chips back into the sockets with your thumbs and try it again. beyond that it could be bent chip legs making poor connection with the socket pins, maybe the socket pins are broken off and only making intermittent contact, or there's a component with a broken off leg or something. I'm not there, I can't say for certain, but hopefully this inspires you to find the answer.
 
Start by cleaning/reseating the graphics EPROMs. Check for corrosion issues with the sockets. As mecha said, you likely have an intermittent issue.
Check your edge connector as well, and measure the voltage at the board when it is running.
 
Do you have another pcb or test pattern generator that you could hook up the monitor with to see if the problem follows?
 
the monitor, no matter how broken it is, will not generate solid colored boxes where the text is. when you're mucking with connecting it to your portable monitor you're probably moving a chip on the board enough to make the graphics cut in and out. my advice is to take the boards out of the cage and the quick and easy and maybe you get lucky solution is to press the chips back into the sockets with your thumbs and try it again. beyond that it could be bent chip legs making poor connection with the socket pins, maybe the socket pins are broken off and only making intermittent contact, or there's a component with a broken off leg or something. I'm not there, I can't say for certain, but hopefully this inspires you to find the answer.
Thanks, you make a good point. Sure, I'll try reseating chips... but note that the "mucking" consists only of inserting Molex pins into a harness connector a couple of feet away from the monitor - and moving that connector around has no effect on the picture. I will also hook up the portable monitor again and poke/wiggle various parts & connectors - if I can recreate the problem on the portable then I agree that the problem is the board

On the other hand, moving the game physically could have dislodged an intermittent contact too, and I misinterpreted the return of the picture problem as something that blew on the second power-up...
 
Thanks, you make a good point. Sure, I'll try reseating chips... but note that the "mucking" consists only of inserting Molex pins into a harness connector a couple of feet away from the monitor - and moving that connector around has no effect on the picture. I will also hook up the portable monitor again and poke/wiggle various parts & connectors - if I can recreate the problem on the portable then I agree that the problem is the board

On the other hand, moving the game physically could have dislodged an intermittent contact too, and I misinterpreted the return of the picture problem as something that blew on the second power-up...
I think Gyruss may have the single wipe sockets that make contact on the outside of the chip legs. those require a bit of finesse to get chip connections right.
 
While we're on the subject of crappy sockets, what do you think of DeOxit D5 spray + removing/reinserting?

Anyway... I'm embarrassed, the problem was not the monitor after all, but at least it's now recapped!
I hooked up the portable monitor and sure enough, now the attract display looked just as bad there. :stop:

So I started tracing backwards from the monitor harness and first found the edge connector was partially burned at the +5 & ground end. Not unusual in many games of the era. Anyway I cleaned that up (someday I should replace it entirely, or at least route the 5 volts through an external connector that can handle the current). Display still strange.

Then I started following the video outputs... something caught my eye in that area - two 330 pf capacitors in the same area were bent over and their hot leads were just barely touching. I straightened that out and what do you know, the display returned to normal! I tweaked a few monitor adjustments and they are close enough :top:

Not the first time in my 60+ years I led myself down the wrong path... oh well, never too old to learn! Thanks again.
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While we're on the subject of crappy sockets, what do you think of DeOxit D5 spray + removing/reinserting?

Anyway... I'm embarrassed, the problem was not the monitor after all, but at least it's now recapped!
I hooked up the portable monitor and sure enough, now the attract display looked just as bad there. :stop:

So I started tracing backwards from the monitor harness and first found the edge connector was partially burned at the +5 & ground end. Not unusual in many games of the era. Anyway I cleaned that up (someday I should replace it entirely, or at least route the 5 volts through an external connector that can handle the current). Display still strange.

Then I started following the video outputs... something caught my eye in that area - two 330 pf capacitors in the same area were bent over and their hot leads were just barely touching. I straightened that out and what do you know, the display returned to normal! I tweaked a few monitor adjustments and they are close enough :top:

Not the first time in my 60+ years I led myself down the wrong path... oh well, never too old to learn! Thanks again.
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these use single wires from the power supply, the sound and CPU boards are interconnected with 2 pin plugs. it's just not enough to get through. that's why it happens. lol I add my own 18 gauge wires soldered into the +5V and ground traces on both boards going back to the power supply. I had to do it on Gyruss at work a few weeks back because the game started locking up.

I was working on Donkey Kong yesterday and I think I figured out how you're supposed to adjust the chip legs for the outer single wipe sockets.
 
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