Author Topic: Chungwa CRT monitor not displaying red (Read 5005 times)

Justin · « **on:** July 26, 2018, 02:49:06 PM »

As I have posted in a previous thread, I have a cal omega amusment poker machine. I have finally found a monitor for it and it was a drop-in replacement for the original. At first the monitor worked fine, then after bringing it from my basement to my living room (may not be relevant but decided to put this in in case it was) the red is now black. I have the 922 revision board from Cal Omega and a Chungwa brand CRT that I got from dormi here on NLG. Please Help

rokgpsman · « **Reply #1 on:** July 26, 2018, 08:04:17 PM »

Flaky or intermittent connection on one of the cables or connectors perhaps? Sometimes when a working machine gets moved and jostled around a problem occurs due to this. Can try disconnecting and reconnecting connectors, cables, etc that have to do with video signal, including the connection at small end of crt (the cathode/gun end).

Justin · « **Reply #2 on:** July 26, 2018, 08:05:41 PM »

I have reseated about every connector on the machine.

rokgpsman · « **Reply #3 on:** July 26, 2018, 08:06:36 PM »

ok, that wasn't mentioned so I didn't know you had done it.

Justin · « **Reply #4 on:** July 26, 2018, 08:12:57 PM »

Sorry, have been emailing with dormi alot about it stopped replying around the 8th of this month so I decided I would post. Any idea is SolidSilver is still around.

Justin · « **Reply #5 on:** July 26, 2018, 08:15:25 PM »

I heard he was great with the machines. Do you want a picture of the issue?

rokgpsman · « **Reply #6 on:** July 26, 2018, 08:38:08 PM »

Quote from: Justin on July 26, 2018, 08:12:57 PM

Sorry, have been emailing with dormi alot about it stopped replying around the 8th of this month so I decided I would post. Any idea is SolidSilver is still around.

I don't think SolidSilver is coming onto NLG anymore but I could be wrong. I think he had some health issues and had to give up a lot of his hobbies. I miss him and he was knowledgeable on the CEI stuff. Send a pm to shortrackskater to see if he knows anything about SolidSilver still being on NLG, he'll know.

Sure, post a photo showing the screen and its problem. It might trigger an idea or suggestion from anyone, photos sometimes help to spark something.

I moved your WTB for the CEI stuff over to the Classified Ads area, good luck!

Justin · « **Reply #7 on:** July 26, 2018, 08:50:17 PM »

Thank you for moving the subject. Here are the picture(s)

https://imgur.com/CK4HOmJ

Justin · « **Reply #8 on:** July 26, 2018, 08:54:47 PM »

Just fixed it uploaded wrong image sorry.

rokgpsman · « **Reply #9 on:** July 26, 2018, 08:56:42 PM »

Quote from: Justin on July 26, 2018, 08:54:47 PM

Just fixed it uploaded wrong image sorry.

ok. (I was wondering about that other image you posted at first - at least it wasn't one that would get us censored!)

Justin · « **Reply #10 on:** July 27, 2018, 09:09:32 PM »

Update: tested the output signal with a converter board and the red was also not there turns out the issue is with the game board. I think I am going to try to replace the Red Potentiometer. Is that a viable idea?

rokgpsman · « **Reply #11 on:** July 27, 2018, 09:27:26 PM »

The pots sometimes get intermittent, the wiper (movable) arm can get tarnished or be touching a worn spot on the resistive portion of the pot. You might try turning it back and forth a few times to see if that does anything for the red signal to come back. If you do this it is a good idea to mark or notice where the pot is now, so that you can get it back to where it is supposed to be. But if you think it is bad and can get another one soldered in there that's also fine.

You can also try bridging the pot with a resistor to connect the red drive signal around the pot, to see if that restores red signal. The resistor size can be something in size of about half the value of the pot. One end of the pot may be connected to ground, so you'd install the temporary bridging resistor across the other 2 terminals on the pot. If you have the schematic you can follow how the red drive signal comes to the pot, then flows thru it and then it goes on to the next stage in the circuit.

Justin · « **Reply #12 on:** July 27, 2018, 09:35:59 PM »

I have twisted it a couple of time, no improvement. Also what does the star mean next to your name where it says online?

rokgpsman · « **Reply #13 on:** July 27, 2018, 09:39:52 PM »

The star means that person is a deputy sheriff here on this wild west Arizona frontier!

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I don't know, maybe it indicates we are NLG buddies.

<but that's just a guess, could be something else>
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Ok, I looked it up, the star means you are under 18 and it's past your bedtime.

Justin · « **Reply #14 on:** July 27, 2018, 09:47:41 PM »

... summer

rokgpsman · « **Reply #15 on:** July 27, 2018, 09:54:27 PM »

oh yeah. 4 more weeks, maybe 6.

Does the red, green and blue drive signal from the mpu board go to the crt monitor board on separate wires, or part of a cable?

Justin · « **Reply #16 on:** July 27, 2018, 09:59:38 PM »

The connector has broken out Red, Green, Blue, Ground, Horizontal Sync, Vertical Sync. in that order. Looking at the cal omega mame page those pots just control the background color. I will still attempt to replace them.

rokgpsman · « **Reply #17 on:** July 27, 2018, 10:04:16 PM »

Are you thinking that the mpu board has a problem with the red drive signal, or that the crt monitor is bad?

Justin · « **Reply #18 on:** July 27, 2018, 10:06:24 PM »

Since I connected the MPU board's video output through a converter board and the Red was also black on that I have deduced that the MPU board has an issue. Both the arcade monitor and the converter board have no red. I believe that this is more than a coincidence.

rokgpsman · « **Reply #19 on:** July 27, 2018, 10:18:11 PM »

I see what you are saying. And it was working fine recently, until the machine was moved to a different location?

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Author Topic: Chungwa CRT monitor not displaying red (Read 5005 times)