Wells Gardner 25K74xx with jumpy picture

smalltownguy2

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Just finished recapping a 7400 from a Killer Instinct cab. The chassis was pulled because the entire image would 'jump' a half an inch or so randomly, leaving blank space on the left side of the screen.

I've gone over this pcb checking for cold solder joints, and recapped it, but the problem persists. What else could cause this image shifting?

A video could be provided if needed....
 
try it with another game board. I've seen some video issues with KI's that were caused by the game board, not the monitor. Might as well make sure this isn't one of those things...
 
I burn tested the monitor all day today on my Double Dragon board. The image is still jumping to the right.

When I got home from work today, the focus had drifted up a bit, I needed to back it off. The image had shifted a bit more to the right, and I needed to turn the horizontal adjustment pot all the way to get the image near center, but it's still not quite centered.
 
if the focus changes on its own, then that's a sign of a failing flyback.

additionally, the adjustment knobs on all these Wells monitors of the U5000/K7x00 era generally turn to shit real quick too. I can't tell you how many U5000s and K7500s I've had to change adjustment pots on the last couple years.

you could try reflowing solder on the remote board, the headers on both the remote board itself and the other end on the chassis where it plugs in to see if there's any change. if you turn the knobs and there's no change, they're broken. I'm guessing you're talking about horizontal position... is that one dead or does it move, or does it move, but not smoothly?

there's some other hardware on the chassis that controls width, it's the 3rd transistor in line on the big black heatsink in the middle. make sure everything's reflowed and solid in that area just for fun. I've never seen that kind of cold solder on these before, but I wouldn't rule it out.
 
i am trying to fix this chassis.

i have changed several caps and replaced the IC U701 with a new one and replaced the H-Hold pot and re-flowed allot of the chassis.

but the problem still has not gone away.

i have flexed the chassis wile it is running but cannot replicate the problem it still does it at random.

what else do i need to look for.

i am not real familiar with these chassis yet and need some expert help.

Peace
Buffett
 
yeah....with the focus changing on its own, the flyback sounds like it is on it's last leg and needs to be addressed. I've seen cold solder on the neck board cause problems but can't remember if it was a shifting issue. There is a transistor that sits over by the verticle IC (I can give you a exact part number after I look at a chassis tomorrow) that I've had to resolder on a couple different chassis's that didn't look like a poor connection but the solder pad was not connected electrically that have given me issues in the past, believe me, even with a magnifying lighted lamp was I able to visually find it.
If you have a spare satellite board and harness, I would exchange it to see if that is the cause. A jumping condition is usually a dirty pot, bad connection, etc.
 
no i don't have another cable and remote board for a 7400:( but i did re-flow the header pins on it. and did change the H-Hold pot on the chassis.

i have not noticed the focus drift that was talked about but i have not left it on for more than 10:00 minutes or so.

also it does not jitter like a bad pot. it shifts the entire image left and right anywhere form an 1/8th to 1-1/2" inches at random.

i have re-flowed allot of the chassis and looked for broke traces but have not found any yet.

so please point out what transistor you are talking about and i will test it and see what i find.

Peace
Buffett
 
FYI - that chassis WAS tested with a replacement remote board and cable (thanks nuterpacman) - no change in behavior.
 
Seen this or similar problem pop up a few times, not sure if a specific solution has been found for each individual case though.
The one I had was definitely in the power supply section, but I never finished doinkin' with it.
You could watch the B+ fluctuate up and down.

One tip that was given to me was to check R108 (.33 ohm 2w) and possibly change it to a (.22 ohm 2w) as a replacement. And to check all associated circuitry in that neighborhood.

But you say it "shifts" left and right?
Maybe I'm thinking of something else....like one that is on the verge of shutdown/ collapsing, so this may not apply to your case.
 
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here is a video of what its doing.
my camera sucks.

http://www.youtube.com/watch?v=BkOUE4FvYB4

from 1:30 to the end is where it does it the most.

i am not shaking the camera that is what the image does. from only a little to allot of shifting.

i did more re-flow and changed out another cap that had not been changed i think that is all of them now and it had no affect on it.

Peace
Buffett
 
Buffett, dust off that haunted chassis, we're gonna send it to the desert to get looked at.

More info to follow....I'll send you a PM.

:D
 
does it move more if the picture is a bright white screen? Put a meter on the b+ test point and see if it is changing. If it is steady, I'd think about trying a different flyback if it seems to move with a change in brightness. Do you have a different tube and yoke you can try it in?
 
Okay, thinking out loud here and haven't noticed what all parts were tried. I saw U701 was swapped, but what about U702? That handles sync processing and you may be getting some weird hiccup in the composite/Horiz sync processing. D702 and Q700 also handle this signal, and have been known to cause problems with picture instability...
 
Thanks for chiming in, Mod, I appreciate it. I'll document these issues for the next guy who digs in to it, as this chassis is in transit to another member for repair. I doubt Buffett wants to play with it any more LOL

:D
 
And this chassis rears it's ugly head again.

I sent it down to P.A.R. in Arizona to have his techs take a look at it.

Here was Tim's response:

Brad,

After replacing some small ceramics that were possible our repair is non successful. Never had one we couldn't do short of a hole in the board. I guess there is a first for everything. Sorry it took a while but we have been really really busy with the regular work picking up and opening the showroom etc.


If you can shoot me your address again I can get it shipped back to you.


I am sorry we couldnt get it going.


Also too to elaborate a bit more. I looked at it personally first, then Paul. Paul is a Master Electronic Engineer so I can be confident (and so can you) a fix is 90% out of the cards. I guess with time invested its probably best to buy another chassis!


Use it for parts.


Thanks

Tim


Anyone else think they can handle this chassis? At this point it's been declared "haunted" and "90% un-repairable" and "a mystery" by at least 3 trusted repair techs.

WTF?

(fast forward to 2:28 in this video)

 
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