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Screen issues


kiwimex

Question

Hi all,

 

Im just starting out on a rebuild with limited knowledge.

 

 

I have a couple of issues with the screen, firstly the whole image sits about 1" off to the right hand side. Im assuming the V-POSI adjustment In my attached photo is for adjusting this, Just missing the plastic cap (can i pull one off the other adjusters and use it on the V-POSI)

 

The image in general is lacking brightness and has slight changes in colour on the edges.

 

 

Would it be best to have a tech look at this or are these issue quite easily fixed? with a bit of research.

 

Are there any CRT techs located north side of Brisbane who are recommended to solve these issues.

 

 

 

Thanks in advance

Steve

 

 

[ATTACH=CONFIG]114533[/ATTACH]IMG_6096.jpg

IMG_6088.jpg

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You can certainly swap knobs over for the V-pos, but if you just use a screwdriver and don't touch the bare metal you'll be fine.

 

Discolouration probably just needs degaussing. There's a momentary button on the distribution block of old LAI cabs, wired to the degaussing coil around the edges of the screen inside the cab. Or it can be wired up to fire when the cab is turned on. The circuit might have gone though, and you can get a degaussing wand pretty cheap. Look up how to use it on youtube. It's a required bit of kit anyway, but if it doesn't solve the immediate problem then the purity is probably off.

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All 60-1 boards do that so its not your monitor which mostly be the board causing the issue.;)

 

It wont degauss if the degauss coil is missing. Don't assume it's actually there. I have seen chassis with the ability, but no coil around the crt.

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The image in general is lacking brightness...

 

In terms of brightness it could be a couple of things...(People with more experience: If I've got anything factually incorrect here please correct me)

 

I've seen issues where a board has had trouble driving an input causing brightness problems. But in that case it was one of those 15k to vga out converter boards where they had the input impedance at 75ohm. Arcade monitors usually have a much higher impedance (1k-10k or something?).

 

Anyway the result in that case was the RGB lines weren't going all the way to ground, causing a sort of offset. Even though in theory this would have gotten rid of detail when colours where at low intensity it displayed like a brightness problem. You could try put a meter on the RGB lines and get a reading when you've got a completely black screen and see if you've got any significant offset.

 

Given its an arcade monitor (i assume) thats less likely to be the problem. I'm not familiar with the outputs of the 60 in 1 boards on the jamma connector, but i guess its possible they have simply used the same levels as the vga out signals. If thats the case they might be a bit too low to drive the monitor properly. If there is some way to find a completely white screen you might be able to get at least a ballpark with a multimeter of full intensity signal level (it will only be approximate as it will probably go back to black level during the h and v syncs). If it is a bit low, you could use a high slew rate op amp to bring the levels up a little.

 

I've had some blank pcbs printed that will take an SOP-14 op amp that you could wire into the jamma harness. If you need one I can send you couple.

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