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craigkeller

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Hey guys, I'm a bit of a noob. Long story short my arcade machine was out of commission for an unrelated issue for the past 4 years. Just got it running again. When I powered on for the first time the screen was kind of dark and a little red. Adjusted the settings and thought I was in business. Well today is day 3 of being back online and I noticed a shadow on the left side of the screen this morning and about 15 minutes later everything black is bright green. Is this thing dying? What could be the issue? The monitor was replaced in 2007 per the service records.
 
Black is bright green, can you still see blue and red? What game is running?

The bright green overwhelms every color but I can still make out blues and reds.

Here's some photos of the issue and the board.

https://photos.app.goo.gl/MMm2wViQQjNsWbyJu6

I'm noticing I don't have a green gain knob and I also see I have a green wire that is just taped off and not hooked into anything. I think that is probably a ground but not sure where it should go if anywhere. The machine doesn't have its original power cable, so I'm worried about connecting it and blowing stuff up if that was done purposely by the previous owners technician.

Edited again: found this post from a guy having a similar issue on arcade controls. I have no idea what any of it means though because I'm so new to this.

Is that three pin molex power for the rGB? IF SO, are the disconnected green wire and the missing green gain knob connected to my issue?
 
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Ok so after researching some more it's either the Lm1203 or the color transistors which are BF871S. I bought the LM, but I can't find the bf871s anywhere. Could someone shoot me a link or a suitable alternative?
 
Maybe first cut the green gain jumper and see if the green colour is removed from the screen - easiest thing to check and reverse. For some odd reason your Green is jumpered or is it actually a broken pot?.. so it means that the green gain is on full blast and that could explain why you have green overwhelming your screen. Going by Occam's razor.


You might then want to add the missing variable resistor pot on the chassis, dial it down and check.
 
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Thanks! I'm looking and all the schematics and other examples of this monitor don't have a green pot. Not saying you're wrong, just wondering if there's another way.
 
I just checked about the specific monitor schematics, I was definitely wrong. It doesn't have a green gain pot.
 
Also of note: I've moved twice since this thing was powered on last.

Ok, so I played with the contrast brightness and screen settings today. If I max out contrast and bring brightness into somewhere in the middle and mess with the screen dial in the back (turning it down) I can get the green to not be as absurd but it also still doesn't look right. The grays are still green in this scenario but blue and red are at least not being completely overwhelmed. I guess the scientific discovery here is that I still have blue and red. Green is just blowing everything out.

Thanks for the suggestions so far!
 
Lowered the green cut off tonight. Very very marginal improvement. I'm gonna replace the LM1203N and check the transistors and see if that does it
 
Where can I find replacement transistors for this thing? They're BF871S. Can't find anything suitable that has the same pinout.
 
just swap the green and red/blue transistors and see if the fault changes
This is a superb suggestion, and I don't see if this was done?

Also, check to see if the green cut-off pot is good (and the right value).
 
just swap the green and red/blue transistors and see if the fault changes
This is a superb suggestion, and I don't see if this was done?
Also, check to see if the green cut-off pot is good (and the right value).
In the process of doing this I found what appears to be a hairline crack between the resistor (R25) and the green transistor (T4). See the latest updates in the album above. Should I run a jumper? Or still swap the red and green to see if it's an issue at all?
 
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Run a jumper and see what happens is my vote. Only take a couple seconds.

If that doesn't change it try swapping the red and green.
 
Ok. Jumpered the R25 and T4. Do I need to jumper the smaller resistor R33 to T4 as well?
They're not labeled on the underside, so I can't quite tell, but taking an educated guess: yes.

It's hard to tell if that crack is actually a crack, or a scratch in the solder mask. You can test for continuity between bits and see if the thing is cracked or not.
 
Taking a break for the day. Really appreciate everyone's help and patience with me. I'm definitely not qualified to be doing this, but I have nobody around to take it to or help directly. Watching a lot of YouTube and frustrating all of you guys haha. trying!

I think the green transistor might be shot. It's a BF859 where red and blue are BF871S, leading me to believe that they've been replaced and green hasn't. I'm also not getting the same resistance readings on green as I do on red & blue. Gonna pick up some BF871S from the UK (UGGHHH) on eBay just in case and revisit this thing tomorrow. If I can't get it working I will have to wait until these transistors arrive in late November.
 
Replacing the green color transistor fixed it! It's not perfect but now I'll swap the green and reds too. I think it needs a cap kit anyways! Thanks everyone!
 
Ok guys, finally all set! Replacing the BF871S transistors fixed the green screen, but when I hooked it back up I had a bunch of other issues.

Ended up doing a cap kit which came with some under-voltage capacitors. Didn't know wtf I was doing so I replaced them anyways and turned the system on which caused a vertical sync/jailbar issue, and my dark left/bright right side of the screen issue persisted.

Just got done replacing all of the under-voltage caps with some I got on mouser along with new small color transistors, a new LM1203N, and IC104. Everything is way better. Still have some minor stuff going on, I can't fix that uneven brightness issue. Nothing I've done has fixed it, but my bias tells me it's less severe now. Could be that all the rest of the colors are back and make it less noticeable.

Overall the monitor feels way more solid. Colors balanced out real well this time using the pots, which wasn't the case before. Really owe you guys a ton of thanks. This was really helpful. In the coming weeks I'm going to check some resistors that looked cracked, the snap in capacitor on the PSU side, degauss to get rid of some uneven color spots, and maybe do the flyback/HOT just because.

I also have this issue where there's gray bars that go across the screen, not sure how to describe them any other way. It's especially visible on the white NAOMI and CAPCOM screens but they are there on every screen. Thought the cap kit would fix but it didn't. Anyone have a similar issue and know a fix?

Here's a link that shows what I mean:
https://photos.app.goo.gl/Yktg898SpDapzVT28
 
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