Issues with 19v1001 B/W Raster Monitor - Space Invaders

LyonsArcade

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Issues with 19v1001 B/W Raster Monitor - Space Invaders

Hi guys;
I've got an old Black and White Wells monitor in a space invaders, and it's got two annoying issues. I've recapped it, but the problems persisted after the capkit.

1. The linearity isn't quite right, vertically... the left side of the screen is a little wider than the right, you can't adjust it out, although the two linearity pots DO affect it and make it better, it just never gets all the way done.

2. The screen rolls when you first power it up, for about 5 minutes, then it locks in. You can adjust the hold and make it stop, but then it'll start rolling after it warms up.


So after the capkit, I went back and checked all the resistors in the vertical circuit. All of them checked out as in spec. Then, I replaced all the Mylar caps in that circuit. STILL the same problems. All of the transistors check out.

Any ideas? Could this be something not in the vertical circuit, or could one of those transistors have drifted slightly or something? You can get a manual online that has a nice diagram of the vertical circuit.... also there are two ceramic caps that I didn't change, but since the mylars didn't affect it I figured what's the point.

Any ideas? Anybody ever worked on one of these? It's hard to find info on this monitor.
 
I went and bought freeze spray, and sprayed all the transistors in that section. 3 of them made it start scrolling again. Yay! So I ordered them from Newark, there were a couple strange ones but I got cross referenced parts so I should be o.k. If this fixes the scrolling, or helps the linearity I'll reply back in case anybody searches this in the future.
 
I replaced 4 transistors, Q210, 213, 217, and 212. Now it works perfect. If anybody has these problems, try freeze spray.

One interesting thing about Q217... on the original monitor, it's an MPU131, and it's installed backwards! There's a little silkscreened diagram on each transistor, but the mpu131 was installed backwards. That's because they messed up when they silked it, however the anode/kathode/gate lines up correctly.

It's hard to find that part, so I ordered a NTE6402. It's a replacement;... but if you check the datasheet, it has the anode/kathode/gate backwards from the mpu131.... which means, you have to install the replacement the RIGHT way, which is really the backwards way. When you're done, it matches the silkscreen (after all these years!) and works great.

Couldn't believe it actually worked, lol. It also fixed the linearity problem, now the monitor looks perfect.
 
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am following your thread , very usefull info here.

i got a taito missile x and the black and white monitor isnt displaying properly.

she is contantly rolling and picture is going all weird like zig zagged a bit.

am going to pull her out tomorrow for a closer look.
 
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