I had great difficulty finding resources describing how to adjust the width of my Playchoice monitor. I found the following article very helpful. Because it is no longer online, I thought I'd reproduce it here to help out others. See my notes after the article.
Adjusting Monitor Widths
By Randy Fromm
Adjusting the width on a monitor can be a frustrating experience. Sometimes the width adjustment doesn't seem to have enough of a range to adjust the monitor the way you want it. the picture may be shrunken in the horizontal direction or stretched out beyond the edges of the picture tube despite your best effort at adjusting it.
Most of the adjustments on a monitor are preformed with potentiometers. A simple manipulation with a screwdriver or finger is all it takes to adjust the brightness, color height (vertical size), and just about everything else. However the width adjustment is made by moving a "slug" into our out of a hollow coil of wire (kind of like a miniature pinball coil). The slug is made from a material called "ferrite," an iron-based compound that interacts well with the magnetic field that surrounds the width coil. When the slug is screwed deeply into the center of the coil, the "inductance" of the coil is increased. That is to say, the position of the ferrite slug deep within the magnetic field makes the coil act as if it is "bigger" (which, electrically speaking, it is). When the slug is fully inside the width coil, the picture size is at its narrowest.
Withdrawing the slug has the opposite effect. As the slug is screwed back out from the middle of the width coil, the inductance of the coil decreases and the picture widens out.
Adjusting the position of the slug requires a hex alignment tool. Don't let the name scare you. It's basically just a plastic allen key. The alignment tools are usually sold in sets of assorted sizes. Sometimes sold as "Color TV Alignment Tools," a set costs around $5 at most electronic parts houses.
Do not use a metal Allen key to make this adjustment! The reason for this warning has nothing to do with getting a shock from the metal wrench touching something it shouldn't. Rather, the electromagnetic radiation from the coil is absorbed by the metal tool and it gets hot as hell if you leave it inserted into the coil for even a minute with the power turned on. When you grab the tool to turn it or pull it out, you burn the heck out of your finger and thumb. (ask me how I know!)
The problem with using a coil for the width adjustment is that the amount of change that can be produced by the full insertion of the slug isn't very much. The range of adjustment is very small. If the width adjustment is not sufficient, the horizontal size of he picture can be changed by a quick modification of the monitor.
In virtually all monitors, there is a capacitor that provides the AC return path for the horizontal deflection coil in the yoke. It's usually easy to spot on the schematic because one side will be connected to the width coil and the other lead of the capacitor will be grounded. The value of the capacitor will generally be in the range of .33 to .53 microfarads at 200 to 400 volts. The width of the picture can be altered by changing the value of the capacitor.
A higher value will make the picture wider. A smaller capacitor will cause the width to shrink. Make sure that the replacement capacitor has a voltage rating that is at least as high as the original. Changing the value +/-20% should do the job.
This modification is especially useful when the new logic in a conversion kit produces a picture that is much larger or smaller than the original. Here is a list of some common video game monitors and the capacitor for each one.
- Electrohome G07 C515 .53 microfarad, 400 volt
- Wells-Gardner 4600 series C615 .39 microfarad, 200 volt
- Wells-Gardner 4900 series C365 .33 microfarad, 200 volt
- Wells-Gardner 7000 series C38 .39 microfarad, 200 volt
- Hantarex MTC900 C69 .47 microfarad, 400 volt
- RGB 1401 C153 .33 microfarad, 400 volt
I wasn't able to find a plastic allen wrench so I used a metal one. Like Randy says, it got blistering hot, so I wore heavy gloves and was fine. If you're adjusting the width by yourself, I suggest positioning a mirror in front of the cabinet so you can see the results while you're tuning.
I didn't need to know or use any of that last stuff about changing capacitors. I only included it because it was a part of the original article. Good luck.