Troubleshooting no-red display on MVS-4-25

[TerryMathews]

I've got an MVS-4-25 cab that is displaying no (or very, very little) red. Before I jump whole-hog into fixing the monitor, I want to make sure that the Neo board is actually supplying a proper red signal to the monitor.

I didn't know until today that the Neo boards can have resistors fail that impair color output. Basically, what I want to do is connect something that I know is good to the cab's monitor and verify that no red is present in the picture.

Any specific ideas for test equipment? I'd like to avoid making permenant modifications to any of my equipment if I can. I don't have access to a known-good Neo motherboard, so it's got to be something else.

Basically, what can I connect to an arcade monitor?

 

[barakka]

Basically, what can I connect to an arcade monitor?

Another game PCB?
You can connect anything that has a RGB+synch output, so a game console or a dvd player with RGB output will do.
You can try to short the red cable with one of the other 2 colors and see if there some difference on the screen, if you get white in someplaces then the monitor is ok.

 

[TerryMathews]

Another game PCB?
You can connect anything that has a RGB+synch output, so a game console or a dvd player with RGB output will do.
You can try to short the red cable with one of the other 2 colors and see if there some difference on the screen, if you get white in someplaces then the monitor is ok.

Ugh x 2. I do get white... On the test screen, I get faint red, green is there but a little out of whack, blue is fine, and white is fine.

Monitor or PCB?

 

[Lime2K]

yeah, if you've got a molex connector between your JAMMA harness and the monitor (which you should, and if not can add fairly easily), pull the red pin out and fire it up again + see what happens. You may want to try pulling blue+green and see if the red changes at all.

BTW, you may want to try cleaning the JAMMA edge connector with QTips and rubbing alcohol and see if that helps the problem -- the harness may be faulty as well. You really shold get another PCB and check that - it could rule out the cabinet completely.

 

[barakka]

Ugh x 2. I do get white... On the test screen, I get faint red, green is there but a little out of whack, blue is fine, and white is fine.

That's strange, because to get white you have to have all the 3 colors, so it couldn't be that one is missing.
I would do what Lime2K suggested.

 

[TerryMathews]

Connecting the red signal from the motherboard to the green line on the monitor does make it appear that the Neo board is outputting red signal, just that the monitor is not displaying it correctly.

I really don't know where to go from here. Should I adjust the tabs on the neck of the monitor?

 

[Tacitus]

GENTLY wiggle your neck board... and I mean GENTLY and VERY SLIGHTLY. If not, you're going to snap it.. There should be a TINY bit of play in it... so try that to see if it works.

It's most likely a bad lead or broken/dirty/loose contact. Trace it back to your neckboard. The POT might also be bad on your red adjust, so wiggle that knob and connector around a bit.

 

[TerryMathews]

I fooled around with the neckboard yesterday, up to and including replacing the transistor that drives red with a new one. No luck though.

This may be extremely silly, as I don't know much about CRTs, but is it possible that the red gun in the CRT itself is dead or jammed? Is there a way for me to wire up like say the green signal to the red gun and see if it fires or not?