k4900 Yellow Screen Then Vertical Collapse

ThunderBunny

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I just got an old Joust cab with Shinobi in it(i'll be gutting it and returning it back to Joust) and my first issue was a yellow screen. I could see some of the game playing in the background. So, grabbed a cap kit and replaced those. But, before that I was monkeying around with the pots and touched a yellow wire that was dangling on the chassis to something and the screen collapsed. Any ideas what I might have blown? Here are a couple pics.
 

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**bump**

So after going through 90 pages in the monitor forum I still haven't found an answer. I'm new, so when the IC3 is referred to, is that IC 301? Haven't found anything on the yellow screen either. I'm assuming I still have that problem still since the line across my screen is bright yellow. Anybody?
 
turn down the screen pot on the fly it is over powering the game image.

you may have blown one or both of the transistors Q302/303 check them and see if hey are bad. you will probably have to pull them to be sure.

on the yellow wire/s

there is a set of 3 posts by the fly that should say.


rite center left on all models
HOR CENT

the yellow wire will go to one of them

and/or another set of 3 posts by the edge of the chassis and another yellow wire that says. not on all models. pending which revision you have.

VERT SHIFT the other yellow wire will go here.
U C D

they control the horizontal and vertical position of the image. one model has a pot instead of a jumper and one model just has the 2 jumper setups.

Peace
Buffett
 
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Do I check it with black lead on center and red on the outer? If I do that I read about .500 on one leg and it doesn't move on the other.
 
red lead on the left leg/base

black on the center/collector.

black on the rite/emitter.

.540ish is what i measure in circuit.

some times they will give false readings in circuit.

Peace
Buffett
 
OK they look good.

check C306 its a little orange/brown drop looking cap see if its open.
check R313 220 310 315 311 221 218 219 216 215 214 314 309 any one of theses may be open.

and check D301 302 303. i have had then short as well. and seen it cause vertical colapse.

then if all that fails look for broken traces on the board and re-flow every thing within an inch radius around both those two transistors. it could be a cold solder joint.

and see this thread that's what i had to do to a 4900 chassis that drove me nuts. worst case senreio tho. for you probably not so much.

http://forums.arcade-museum.com/showthread.php?t=209526

Peace
Buffett
 
Ok, I will give those all a check tonight. Thanks for the pointers. I read through that post, looked like a nightmare.
 
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Still collapsed after changing three resistors out... Should I be getting a number on my meter with D301, 302, 303? 301 just looks like a wire so I assumed it would read 0, 303 is reading 0 also.
 
ok silly question did you put the jumper back on one of the 3 posts labeled
U C D.

now serious question have you checked. R375, 384, 372.
and caps 301, 306.

after that i would sub out IC301 you may have blown it.

also have you verified all the traces to make sure one did not burn open.

Peace
Buffett
 
Haha, yes. That moved my vertical line up and down. I have checked all the ones you mentioned earlier. I'll check the ones you just told me about tonight. When I first pulled it out I got bits of what looked like a ceramic disk capacitor. Are there any of those that would affect the vertical? I need to fix this because my wife said no new machines until I get one of my monitors working. lol
 
Ok, so for giggles I just replaced every resistor and still nothing. It looks like IC301 may be out. None of my voltages match the manual. I'm assuming that would mean its out?
 
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