k4900 monitor problem - bright yellow screen and nothing else

jehuie

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k4900 monitor problem - bright yellow screen and nothing else

So I've got this monitor that I've been trying to troubleshoot with no luck. It comes on with the entire screen bright yellow. Then it slowly fades to a less bright shade for a second or two. And then it suddenly gets bright yellow again. Can't see anything else. Turning the brightness and focus knobs all the way either direction makes no difference.

Fise F501 is good.

Voltage at R503 is +150 volts so that looks good.

Any tips on what this might be? Thanks!
 
And to clarify....there is no image at all. Does that sound like a flyback issue?

I had something very similar recently, caused by a cracked trace on the neck board (!)
The video B+ was getting to the neckboard, connector was fine, but testing the voltages at the R412 revealed the problem, crack right across the trace before R412.

- James
 
150vdc is way to high for your B+ it should be 130vdc.

check it again on the leg of the resister closest to the fuse.

Peace
Buffett
 
have you capped it and measured all the big resisters to see if they are all good and in tolerance.

sounds like it is a failing resister and or caps to me.

Peace
Buffett
 
have you capped it and measured all the big resisters to see if they are all good and in tolerance.

sounds like it is a failing resister and or caps to me.

Peace
Buffett

I have not yet capped it. I'll order a cap kit for it and I can measure the resistors in the meantime. Someone else told me it sounded like the tube is likely shorting out inside though. I'm thinking this sounds right, especially since the brightness control seems to have absolutely no effect on it and the entire screen is glowing yellow.
 
that is a possibility.

i have had several tubes do that kinda thing but i always had a pic on the screen of some sort.

wile you are waiting on the cap kit i would try and get the tube checked.
or hook a known working chassis up to it and see what happens.

Peace
Buffett
 
Don't have a spare chassis unfortunately. I need to find a plug for my rejuvinator that will work with arcade game monitors. I bought a B&K a long time ago but have never had a chance to even try it since I don't have any of the more popular adapters for it. :(

that is a possibility.

i have had several tubes do that kinda thing but i always had a pic on the screen of some sort.

wile you are waiting on the cap kit i would try and get the tube checked.
or hook a known working chassis up to it and see what happens.

Peace
Buffett
 
I had something very similar recently, caused by a cracked trace on the neck board (!)
The video B+ was getting to the neckboard, connector was fine, but testing the voltages at the R412 revealed the problem, crack right across the trace before R412.

- James

YES! Jrok nailed it. There was a crack on the neckboard. Jumpered wires across the cracked section and presto....fully working Robotron!

Thanks guys! I couldn't do this stuff without you!
 
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