Super Video 2.1XL
From the pen of AC's "occasional columnist" Ben Poehland comes the final, gutwrenching word on cleaning up video problems in all the XL-series computers, as The Alchemist brutally reveals the scandalous acts of the Sunnyvale Butchers. Clean video at last for the 600XL, 800XL and the 1200XL owners!
S-V 2.1 for the 800XL
If you have a RAMBO or other memory upgrade card installed, unplug it and keep it out of the way. Refer to Fig. 5 for the following steps:
Step 1. Locate 820uH inductor L5, usually a green-colored component that looks like a resistor with gray-red-brown-silver bands, directly in front of the 4050 chip U20. De-solder or snip out this part, then clear the vacated board holes with a solder sucker. Select a 2.2-ohm resistor (red-red-gold-gold), solder it in place of L5, and snip off the excess lead length. (This improves current flow to the entire video circuit.)
Step 2. Locate electrolytic capacitor C50 (10uF/10V): it's adjacent to the L5 inductor you just replaced. De-solder this capacitor and clear the vacated holes of solder. Replace C50 with another electrolytic capacitor of at least 100uF/10V rating. Radio Shack parts vary considerably in their physical dimensions, so when you're shopping be sure to examine all the parts packages in the range of 100uf or 220uF of radial-lead electrolytics on the shelf in the store. Select whichever gives the largest UF value in the smallest physical size. I was able to squeeze in a 220uF unit and still didn't have trouble reinstalling my RAMBO hoard. (Restores AC filtration lost by removal of L5.)
Step 3. Locate 2K resistor R52 (red-black-red-gold) directly to the left of Q3 on the motherboard. Remove this resistor and replace it with a 2.7K resistor (red-violet-red-gold). (Improves color saturation slightly.)
Step 4. Solder a 1K resistor (brown-black-red-gold) from the right side of 100pF capacitor C55 to the bottom end of 6.2K resistor R58 (blue-red-red-gold). This resistor has to traverse about 1.5" of board space, so don't trim the leads. Mount it about 1/4" above the board on the component side, bending the leads down at the specified contact points. This resistor provides negative feedback around the color amplifier Q2-Q4-Q5. The effect is subtle, but it improves saturation a little and reduces color shadows somewhat.
This completes Super Video 2.1 for the 800XL. You'll probably find it necessary to reduce your display brightness controls when you perform your checkout, as the video signal is now stronger than it was with S-V 2.0. Check out the improvement on a color monitor if available before you close up the case. Use the luma-chroma interface to check proper operation of your chroma circuit wiring. For my color check-out I just stuck my Pole Position cart in the slot and booted up the bare board. Pole Position is nice because it's very colorful and self-starting. The display was wonderfully sharp and brilliant on a Commodore 1084 using the luma-chroma interface with composite video disabled. The Alchemist succumbed to several hours of game-playing after reassembling the computer. Unfortunately the crisp display didn't improve my driving, and those fiery crashes were all the more annoying for their clarity. Hrrrumph!
Copyright © 1993
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