Fully rebuilt chassis, blue flashing bars issue

DuffCon

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I has this chassis rebuilt by Buffett about 2 years ago. I recently noticed an issue Sometimes there will be a random flash of a blue horizontal bar, Just a solid bar or a flash of a blue screen. No other video issues.

At first I thought it was an issue with a new Neo Geo board I just installed, so I began to t/s from that. Today it occurred to me to just try another JAMMA board and sure enough, the issue still happens. I managed to capture some videos of the issue here. The first 2 are my MVS, the 3rd is a Pandoras box I have laying around.

Watch the second hit by Earthquake, looks like a bar
https://youtu.be/QhKPf2o5E2Q

Here on a unibios crash screen, looks like a blue wipe
https://www.youtube.com/watch?v=mUjcvQTLs9U

and here on the menu screen of a pandoras box:
https://www.youtube.com/watch?v=Njby64HdsQs

Given I've tried two PCBs it's got to be monitor related. Does anyone have any ideas where to start?
 
So I'm not ready to call this fixed, but out of desperation, I swapped out the power supply with a spare. The old one was from 1990 and was rather loud. After the change, I ran it for at least 30 mins and have not seen the same issue. Before it would usually show up within a couple of minutes.

****edit****

Issue still happens, though it seems much less frequent and intense. Wondering if the cheap Chinese power supply still doesn't cut it?

I took apart the old PS and can see there are some caps and resistors they have seen some better days:

5ae9375f524d0884fb39b61c3ad47419.jpg


R49 is melted:

e21a465333182b3f770efcd97817251b.jpg


Backside:

e717cbcd87dfd4a35c8ec63c1d5b64a8.jpg
 
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you definitely have bulging, cold solder joints and leakage which are all very bad signs and they need to be replaced or replace with a quality P/S.
 
New update. I decided to vet everything power-wise and found a bad ground on my ac cable. Replaced that, and now have everything grounded correctly. Still no Help.

Also discovered a one of the 4-5v lines is not run off my Jamma harness which is not good so I'll get that fixed tonight. Also ordered a Happ power supply as I really don't trust the $13 Chinese PS.
 
Another update. Per Buffet, I measured the voltage on the 74xx chips on the board, I got the same voltage as the edge (5.2v)

These were the chips:

SN74AS04N
74HC04A

Also repaired the unterminated +5v line, still happens



Any other ideas?
 
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I don't think you have a power supply issue especially since the different game boards are working and you are getting 5.2 volts.


My guess is that you have a short in the tube. If you have a rejuvenator, you can verify it. Sometimes you may be able to see a small flash in the neck of the tube when the blue flashes appear on the screen.
 
I don't think you have a power supply issue especially since the different game boards are working and you are getting 5.2 volts.


My guess is that you have a short in the tube. If you have a rejuvenator, you can verify it. Sometimes you may be able to see a small flash in the neck of the tube when the blue flashes appear on the screen.

Yeah, i'm running out of things to try. It's so odd because from what I understand tube shorts tend to look like off/weak/no colors or focus issues. This is intermittent. Otherwise, the picture is beautiful.

I'm going to swap chassis with my other K7000 25" and see if the issue moves. If it doesn't then i'm out of things to swap. I'm really hoping it's not the tube, it's a bit intimidating to source and swap it.
 
Yeah, i'm running out of things to try. It's so odd because from what I understand tube shorts tend to look like off/weak/no colors or focus issues. This is intermittent. Otherwise, the picture is beautiful.

I believe it's a little different. Do you have access to a rejuventor to check for a short with the blue gun?
 
Could just be poor solder on the respective neckboard transistor.

Anything is possible, but I don't think so in this situation. If the transistor for the blue was bad or cold solder, he would lose the blue color on the screen.
 
I believe it's a little different. Do you have access to a rejuventor to check for a short with the blue gun?

I don't have one or know of someone in the area with one. I know there are a lot of Bay Area Forum members, so maybe someone will throw me a bone in exchange for beer.
 
So I swapped the chassis with another k7000 to test. When I pulled out the chassis in question, the first thing I noticed was the linearity coil was broken. Because the chassis is oriented downward in this cab, the coil seemed to be leaning forward and possibly having intermittent shorting with the 3rd pin. In this pic I already had bent it back:

e7c6f82a727de4e693f7ecc6261033bd.jpg


So after bending it back and completing the swap I ran both cabs for about 30 minutes and neither had any issues.

I wrapped the 3rd pin with some shrink tube and used some RTV silicon to glue the coil in place and replaced both chassis to,their original cabs. So far I haven't seen any issues.

Oh, and count me among the people bit by a supposedly discharged tube! [emoji37]
 
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Sorry to say that the issue is still here. This is really staring to get me down. It seems less frequent, but I'm officially out of ideas.

:(
 
Sorry to say that the issue is still here. This is really staring to get me down. It seems less frequent, but I'm officially out of ideas.

:(
So your saying the issue happened to one tube with 2 different chassis's? So then the issue is isolated to the tube? If so thats much better than the issue being the chassis. K7000 25 inch monitors are about the easiest to do a tube swap on. Find a 25 inch TV, most are a direct swap. You can usually find them in thrift stores for about $5. This is a very easy fix.
 
Actually not sure. When I swapped the issue did not move to my other cab. I should have done more extensive testing. When I find the coil issue I jumped to the wrong conclusion. I guess the least thing to do is swap again m, but run it for a lot longer time period.
 
Actually not sure. When I swapped the issue did not move to my other cab. I should have done more extensive testing. When I find the coil issue I jumped to the wrong conclusion. I guess the least thing to do is swap again m, but run it for a lot longer time period.

Yeah, I would do the swap again and run for a LOT longer.

Make sure you are "QA" testing the monitor by playing the game while it is on. You have to change as many pixels around as you can. ;)
 
Swapped chassis again, issue stayed. Right now it seems like the issue is a lot less frequent, so I left as is. Will test some more.
 
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