K4900 Weird Screen

TwiSTed216

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Hello. I have a ghosts and goblins game in a Robotron cab with K 4900 monitor. After playing the game for about 15 minutes Blackwood start creeping in on the lower right portion of the screen. It never consume the whole screen but about an eighth of it. There was also a horizontal line in the middle of the game that's graphics for the store did a little bit. I replaced all the capacitors and found that eight of the 17 were bad and one of the other capacitors was rated at a 3.3 microfarad when the schematics of 2.2. The capacitor was see 308. I booted up the game and the screen is very dim with some horizontal stationary zig-zagging lines that seem to scrunch up more towards the bottom of the screen. See photos. The screen is also very dim.
 

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turn down the screen pot on the flyback.

use my video to help you color and white balance your monitor.

start at the 18:00 min mark.



Peace
Buffett
 
So I watched the video and I'm assuming your advice is to check the boards 4 bad joints checking it particularly the transistors and potentiometers? Is my screen with skin
 
the 4900 suffers badly from cold solder joints.
a re-flow of the chassis and neck board is needed.

did you turn down the screen pot on the flyback?

Peace
Buffett
 
after a cap kit you have to readjust everything normally, so going through buffett's video will cover most everything for the proper color balance.
 
Yes I adjusted the flyback and that's how I was able to get a picture. But it didn't get any brighter then what's in the picture and it has the white stationary zigzagging lines going through it. I just pulled the turkey out and I'm going to resolder all the joints. I would think I would need to readjust the monitor since almost 50% of the cats were bad in the picture didn't look too bad
 
It's looks great! Thanks! I resold red the neck board and all pots and transistors and pins. Boom! If you look at the pic, it looks great. The only thing it seems like the picture can be bigger on the monitor. It doesn't seem like it's using the full monitor. Any advice?
 

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It's looks great! Thanks! I resold red the neck board and all pots and transistors and pins. Boom! If you look at the pic, it looks great. The only thing it seems like the picture can be bigger on the monitor. It doesn't seem like it's using the full monitor. Any advice?
 
There is a "vertical size" pot on the chassis. With it in the game, it is on the left side, with 3 more pots right next to it.

It's either the 3rd or 4th one from the left, can't remember.

You adjust this with the game on. Watch your fingers. Use a friend holding a mirror to help guide you, or just check back after each little twist and wing it. A lot goes a long way, so go slow.
 
you have to adjust your Horizontal width coil.

it is the black tower in the center of the chassis with a copper coil wound around it.

you HAVE to use a PLASTIC allen wrench or you WILL break the ferrite core inside the tower.

also if you use a metal allen you will burn the S^%T out of your fingers.

many times on the 4900 chassis you should NOT adjust this coil as they are fragile and will break VERY easy!!

plus they can be stuck from heat and warping of the coil housing so they will not turn any way

does your monitor bezel cover any of it?

your image looks fine as it is widthwise.

in G&G you need to see what is coming at you at all times, it is hard enough without having a hidden enemy you would normally see coming.

if it really bothers you you can try and change the width cap.
there is no set value cap that will fix the width, you will just have to try different combinations of caps till your happy.

but personally, i think it looks fine.
i have many games adjusted to look like that and enjoy seeing the entire game on screen.

if you need width caps i stock them and can build you a nice kit.

Peace
Buffett
 
So far you guys have been right on and have made this very simple and I think you greatly!! 2 final issues I hope someone can give some guidance on to help me out. I'm at a loss right now. ='(

k4900 monitor the right border of the image is scrunched up instead of being stretched out. I can take a picture of it later but the screen looks great until you get to the last quarter inch has the picture scruntched up. The edge of the picture needs to be stretch out. Any ideas?

Also, the K4900 is loosing the green color. It goes on and off. My 20EZ on my Donkey kong does the same thing but with the red channel. The Ghost and Goblins game had all the colors working fulltime until I did the cap kit. I dont think it has to do with the new caps but might have aggravated something else? Clueless as to where to start and what to test.
 
So far you guys have been right on and have made this very simple and I think you greatly!! 2 final issues I hope someone can give some guidance on to help me out. I'm at a loss right now. ='(

k4900 monitor the right border of the image is scrunched up instead of being stretched out. I can take a picture of it later but the screen looks great until you get to the last quarter inch has the picture scruntched up. The edge of the picture needs to be stretch out. Any ideas?

Also, the K4900 is loosing the green color. It goes on and off. My 20EZ on my Donkey kong does the same thing but with the red channel. The Ghost and Goblins game had all the colors working fulltime until I did the cap kit. I dont think it has to do with the new caps but might have aggravated something else? Clueless as to where to start and what to test.

your color going in and out could be the tube or chassis. its best to test and verify which it is by swapping another chassis if you have it. if its the tube you may be able to fix it with a rejuvenator. the chassis is my first guess and that could be a cold solder joint on the input header pins, or the transistors or the transistor going out under load and if you swap the green transistor with the red or blue and the problem follows the transistor you know its bad. slim chance but the signal from the game pcb may not be getting to the monitor which i would rule all the other things out first since they are more likely the problem.


BTW: the scrunching on the side could be a deflection issue and may have a cold solder joint or a failing transistor.
 
Thanks for the guidance. I have plenty of things to check when i get home. I am guessing it is with the tube or chassis too since it wasnt doing it until i replaced the caps. I am hoping to find the issue since the picture looks great when all the colors are there! I will keep you all posted as to what I find.
 
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