Test Patterns-hc™ is a
short program that provides an acceptable substitute for a color bar/dot generator. It is written for the C-64 but is easily con verted to the VIC-20. 10 PRINT CHRS(147);:POKE
53280,0:POKE63281,0:FOR1 = 1 TO 24
20 PRINT"{CTRL»}{CTRL3} {7 spaces} {CTRL 7} {7 spaces}
{CTRL 8} {7 spaces} {CTRL 6}
{7 8paces}{CTRL 2}{1 spaces} {CTRL0}":NEXT 30 GOSUB200
40 P0RI-1 TO24:PRINT
"{40 periods} ";:NEXT
50 GOSUB200
GO F0KU1 TO24:PRINT
"{40SHFT+}";:NEXT 70 GOSUB200 80 GOTO 10
200 GET A$:IF AS =
HIEN 201)
210 PRINT CHR$(147);:RETURN
To change screens, hit any key. For the VIC-20, change line 10 to read: 10 PRINT CHR$(147);:
POKE36879,8:FOR I = 1 TO 22
Instead of seven spaces in line 20, use four spaces. Change lines 40 and 00 to read 22 in stead of 40 in the Print statement.
Terrill S. Barkley Columbus, NE
Color Video
colors coming from your com puter are very good, but the control settings on your TV or monitor can make a big differ
ence in their appearance. To set your display correctly, follow the procedure below. • Use the Test Patterns trick to get the vertical color bars on your screen.
• Turn the brightness control all the way up, then turn it down until the background is totally black. • Adjust the color control until the bars have a good color intensity. • Use the tint control to set the bars to the correct colors. On
the C-64, a more sensitive test can be had by changing the test program so the color bars are purple, orange, brown and light
red. (See p. 57 of your user's guide.) • Go to the Crosshatch pattern and set the contrast to a pleas ing level.
126 • RUN Special Issue 1985
• Repeat all steps until you have optimized your display. Gene Casanova Wauwatosa, WI
Color Convergence Test-
To maximize the definition in a color display, the electron beams coming from the red, blue and green guns must be properly aligned. The adjust ments that align the beams are called static and dynamic con vergence, and they should be made only by a qualified technician. To evaluate the convergence of your own color display, you can use the Test Patterns pro gram trick. Put the Crosshatch pattern on the screen and turn the color control all the way down. If you see a Crosshatch
keeps the outer screen columns inside the edge of the picture.
But monitors made for text displays do not overscan. In fact, they underscan, to make sure that no character is ever lost. When you put a Commo dore signal into such a monitor, you get more borders than you bargained for—Commodore's overscan-protective border, plus the CRT's undcrscanned outer edges. Correcting the problem is sim ple in many cases. Some highquality monitors are designed for TV and data use, with a size switch on the back panel; just set it properly, and the problem will go away.
Most other monitors have a
vertical size control on the back panel and a horizontal size con
pattern is also useful for making
trol inside the cabinet. Often, these can be adjusted so the useful screen area fills the CRT. Adjusting them is simple and straightforward for anyone qualified in electronics, but dangerous for everyone else. The vertical size, or height,
vertical height and linearity ad
control is usually a screwdriver-
justments. These are usually
adjustable potentiometer; just turn it until the top and bottom
composed of white lines, your
convergence is all right. If, however, the lines are not all white, the beams are missing their targets, and your monitor needs its convergence adjusted. By the way, the Crosshatch
found on back panel controls, and they can adjust the shape
of the black border move out
of the squares in your cross-
ward off the screen.
hatch pattern.
Usually, horizontal size, or width, is controlled by an iron slug in a coil near the high-volt age flyback transformer; it may or may not be labeled. If it isn't, your monitor's schematic dia gram should help you identify
Burt Fisher Forestdale, MA
Adjusting Picture SizeWhen Commodore computers are used with certain video monitors, you see the Commo dore screen area, surrounded by
the Commodore border, sur rounded by yet another (black) border. As a result, the usable screen display covers only a fraction of the CRT area, and the characters are much smaller than they might otherwise be. Here are the reasons for the problem, along with a sug gested cure. Displays for TV viewing are adjusted so the outer edges of
it. Unscrewing the slug will usually expand the picture; don't touch it unless you've worked inside a TV before— there are dangerous voltages
very close by. On my Taxan monitor, I re moved the slug entirely, which brought the Commodore border just to the edge of the screen. Replacing the iron slug with a brass one moved it even farther outward.
If your monitor dealer has a repair department, they should
the picture slightly overlap the edge of the CRT. This is called overscanning, and it's done to gain certain technical benefits; losing part of the picture is the price you pay to gain them. Since losing your screen data to
be willing to make both adjust ments for you, and to guarantee their work. If you make them yourself, you do so at your own risk, but your actions are un likely to harm your equipment.
overscan would be unaccept
Pat Bilker
able, Commodore's border
McKeesport, PA