K4800 No Picture After Weird Symptoms

parkway

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So the other night, my wife is in the basement playing Phraze Craze. Has a K4800 monitor with a pretty decent picture on it. All of a sudden, the brightness goes up, picture gets blurry, and colors start bleeding; I'm next to her watching this happen. Not quite sure what's going on, I switch the game off. I wait five minutes, and turn it back on. Game is now playing blind. I have neck glow and the high voltage is obviously there as I get the usual CRT static sound when I turn it on. But no picture. Not even a faint image. I ordered a cap kit as from the looks of it, no one has touched this monitor in over 30 years, but this seems like more than caps. Anyone seen this before? The symptoms prior to it not working have me concerned that the tube took a shit. Thanks.
 
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i would check the B+ first and see what you have. make sure your putting in good quality cap kits and if you need them in the future i have them nichicon 105c 100% and in stock.
 
Where is the best place to get a B+ reading on one of these?

Wells gardner 4900 - 130vdc check with meter black lead on chassis ground and red lead on the blue wire R503 (large ceramic resistor mounted on frame) or red to TP91 in the back center of the board.
 
Got it. Thank you. I'll check it out and report back.

I should also add that I've checked the connection from the pcb to chassis and tried a different PCB with the same result; definitely the monitor.
 
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Getting around 165v. I'm guessing that's a problem.

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check the 130v circuit J33 jumper wires and others in the center back area of the pcb.
 
Ok thanks guys. Pulled the monitor out of the cabinet before work to make it easier to pull the chassis. I'll start monkeying with it tonight and see what I can see.
 
Ok well my assumption that no one had been in this monitor its entire life was dead wrong. Looks like someone cracked the chassis in half at some point and jumpered all the traces across the crack. Lovely, but it was working fine for a while, so I guess they did ok.

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I guess another question would be since the thing was badly damaged at some point, should I just cut my losses and find a "new" 4800 chassis and drop it in and save this one for parts? Is a chassis like this just more headaches waiting down the road?
 
check the traces and see if a another trace along the break may have finally broke after all these years working.
 
Tested the voltage regulator (STR381) per Buffet's instructions in his excellent video:

https://youtu.be/XhwuHF-ffpE

I get .619 on one outside leg to the case and .567 on the other outside leg to the case. However, I do NOT have a dead short between the two outside legs themselves. I'm guessing this means my voltage regulator is bad as was previously thought. If so, generally speaking, is this the cause of the problem or could it be a symptom of a larger problem?
 
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I guess another question would be since the thing was badly damaged at some point, should I just cut my losses and find a "new" 4800 chassis and drop it in and save this one for parts? Is a chassis like this just more headaches waiting down the road?

my opinion if it was mine is i would replace the chassis with that much damage. if you have a couple cracks thats one thing but dozens that require that many jumpers means it can be a night mare down the road and usually anytime you have to handle it you run the risk of causing more. (if it was a rare chassis then i would consider keeping and fixing but k4800 are pretty common).
 
my opinion if it was mine is i would replace the chassis with that much damage. if you have a couple cracks thats one thing but dozens that require that many jumpers means it can be a night mare down the road and usually anytime you have to handle it you run the risk of causing more. (if it was a rare chassis then i would consider keeping and fixing but k4800 are pretty common).



Gotcha. Makes sense. I'll keep my eye out for one for sale. In the meantime, I'll throw a new voltage regulator in this one and hope it fixes it. If not, I'll stick another monitor in Phraze Craze. From what I described above with the regulator, you would agree that it's bad?
 
that chassis is fine, once repaired it will last just as long.

i have repaired many chassis like that and they are still running strong.
i did a 4900 with 19 jumpers on the chassis and 17-19 on the neck board.
http://forums.arcade-museum.com/showthread.php?t=209526

bad caps and cold solder joints on that chassis will keep it in HV shutdown.
until it gets caps and a re-flow you will not have a good starting point.

the 4800 is not an impossible chassis to find, but you will be waiting a wile or paying for another that still needs the same work as yours.

if you don't want to mess with it, send it on in.
i will take care of it.

Peace
Buffett
 
that chassis is fine, once repaired it will last just as long.



i have repaired many chassis like that and they are still running strong.

i did a 4900 with 19 jumpers on the chassis and 17-19 on the neck board.

http://forums.arcade-museum.com/showthread.php?t=209526



bad caps and cold solder joints on that chassis will keep it in HV shutdown.

until it gets caps and a re-flow you will not have a good starting point.



the 4800 is not an impossible chassis to find, but you will be waiting a wile or paying for another that still needs the same work as yours.



if you don't want to mess with it, send it on in.

i will take care of it.



Peace

Buffett



Thanks, Buffet. I'll give it a whirl and if it still doesn't work, you can expect a chassis in the mail. :)
 
Awesome!!

good luck on the adventure!!

hope all goes smooth.

keep us updated.

i will be there if it does not want to cooperate.

Peace
Buffett
 
FWIW if the votage regulator is not properly loaded down you may get a high result like that.

I agree with buffett, thats fixable and probably has more cracked traces and cold solder.
 
Looks like we're back in business. Changed the STR381 and reflowed the 130v rail, the resistors, headers, and anything else that looked like it might need it. Capped the chassis. Buzzed out the jumpers (a bunch of which I had to disturb during the cap kit) and all looked good. When I get my TPG, which should be soon, I'll dial it in better. Letting it run for an hour before bed to test it.

A few of those caps were toast. One in particular had a green tint to the top and was generally almost mushy.

Thanks very much guys. As always, I appreciate the help and learned something along the way.

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https://youtu.be/GJvyjMJTzLo
 
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