Moon Patrol - K4900 - TOO RED!

blkdog7

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I am not sure what else to do to this monitor. A few months ago my Moon Patrol's monitor started turning all red as it was on. So, I pulled it, capped it, and replaced the transistor that drives Red on the neck board. I also reflowed the solder on the neckboard and in most places.

Now, a few weeks later, it's doing it again! I know there are some red transistors on the main PCB of the monitor. Is it those? Or, could this be something else?

It looks like this:

8129293290_794a0fb59d_b.jpg
 
It could be pretty much anything (resistor, cap, transistor) in the red circuit on the main board or neckboard, and it could be the tube (not likely though, yours doesn't look like a tube problem, usually it'd have retrace lines).... or it could be the gameboard itself.

I'd focus on testing the stuff on the neckboard. You'll see that there's three sets of everything, one for each color... so check the resistors against each other and see if any of them are messed up.
 
If the monitor was slowly going red. you might want to get some freeze spray and just shoot the red transistor and see if you can isolate the problem.

It could be a dirty pot.

You might want to check q02 or q07. If you swap the red transistor with the blue or green and the screen changes to an over driven blue or green. you will know that it the red transistor on the board that need to be replaced.
 
i have a 4900 in my MR DO! and it did the same thing.

i rebuilt the chassis and it still did it. swapped out the chassis with a known good chassis and it did it with the second chassis as well.

rejuve the tube. that was my issue and ever since i rejuved the tube it has not done it since.


Peace
Buffett
 
I'll rejuve the tube and see what happens.

BTW - what usually happens with this game is that when I turn it on the picture is usually perfect. Deep black background. The longer the game is on, it starts flickering from the black background to the red color you see. I'll see horizontal red lines too as it's flickering. Eventually it just goes completely red like the photo.
 
I'll rejuve the tube and see what happens.

BTW - what usually happens with this game is that when I turn it on the picture is usually perfect. Deep black background. The longer the game is on, it starts flickering from the black background to the red color you see. I'll see horizontal red lines too as it's flickering. Eventually it just goes completely red like the photo.
that sounds like a classic tube shorting the red. rejuv and you shound be good. you can also pull the red drive transistor off the neck board and try it again to verify its your tube.
 
I am still trying to fix this damn thing.

I have replaced all of the color transistors. Three on the neck board and the six on the main PCB. It's still turning red after 30 minutes or so. The picture on this monitor is AMAZING when it's working. It's just that after the game warms up or heats up the monitor turns all red. Ugh!

Also, I verified that this is not a PCB issue but it is a monitor issue for sure. If I disconnect the video signal from the PCB when the monitor is red it stays red with no video signal.

I also hooked up my Sencore 7000 to the tube and it passed all tests. I did do a slight restore on it but it didn't do anything to help this issue.

I just got done going back through the chassis and reflowing everything I could and also testing components in the areas where the color circuits are. Haven't found anything bad yet.
 
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that sounds like a classic tube shorting the red. rejuv and you shound be good. you can also pull the red drive transistor off the neck board and try it again to verify its your tube.

Ok, done relflowing and I decided to pull the red transistor off the neck board before I stuck it back in and the game is running now. Let's see if it turns red again. Good idea, thanks!
 
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Did you resolder the joints on the neck board?

Yes, I did. I went over ever single one.

I just ran the game for an hour without the red transistor. And, it never turned red. So, the tube is good, I'd say.

Now, I never tested the game with the red transistor and after my reflow session this morning. Gonna put the red transistor back in and see if maybe I did fix it when I reflowed like a mad man. Putting it back in now, wish me luck...
 
Swapped neckboards with a junker 4900 chassis I had in the garage. NO CHANGE! So, it's on the chassis somewhere!
 
Just for the hell of it I put my Sencore CR7000 back on the tube. The tube tests great, no shorts, etc. It passes all tests.
 
Just for the hell of it I put my Sencore CR7000 back on the tube. The tube tests great, no shorts, etc. It passes all tests.

There's not a heck of a lot in the color circuits for 4900's.

Check Q203, Q206, and D207 on the chassis. Those are for the red.

If you want to swap them around with other colors to see if/where the problem follows.

R: Q203, Q206, D207
G: Q204, Q207, D208
B: Q205, Q208, D209

So, if you swap Q203 and Q204... and the screen goes green instead of red... there ya' go. It's a little tedious... but since it's not acting up all the time, you might not be able to just take a meter to the transistors and diodes and be sure that they're good.

I'd check the latter ones first (Q206, Q207, Q208).
 
There's not a heck of a lot in the color circuits for 4900's.

Check Q203, Q206, and D207 on the chassis. Those are for the red.

If you want to swap them around with other colors to see if/where the problem follows.

R: Q203, Q206, D207
G: Q204, Q207, D208
B: Q205, Q208, D209

So, if you swap Q203 and Q204... and the screen goes green instead of red... there ya' go. It's a little tedious... but since it's not acting up all the time, you might not be able to just take a meter to the transistors and diodes and be sure that they're good.

I'd check the latter ones first (Q206, Q207, Q208).

Thanks for the info. I already replaced Q203, Q206, and Q401 already. I also replaced the Green and blue equivalents of these.

I'll check D207!
 
I think I fixed it. I replaced D207 and have let the game run for 45 minutes now. NO RED!! WOOT!

THANKS FOR THE HELP!!!

8243173802_2a0bf1f5a9_b.jpg
 
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