Zenith SM-ZVM-122 Service Manual page 22

Page 6-2
SYMPTOM
Only top or bottom of vertical deflection present.
Horizontal scans right to left instead of left to right.
Vertical scans bottom to top instead of top to bottom.
No horizontal or vertical sync.
No characters on screen.
(High and low voltage OK)
ADJUSTMENTS
Video adjustments are located behind the front
panel access door and on the rear panel. The B
+
Voltage adjustment is located on the main board.
Refer to Figures 6-1, 6-2, and 6-3.
To adjust the Video controls, use the Display/Key-
board Test, or the ZBASIC Program to fill the screen.
DISPLAY/KEYBOARD TEST
If your Z-100 Computer has the diagnostic ROM (HE
444-87-5)
at location U190, you may use the Display/
Keyboard Test to fill the screen.
• When the prompt appears, type
T.
• Select the Keyboard Test.
• Type any character and it will fill the screen.
.• Press the DELETE key to exit.
AREA TO CHECK
•
0601, 0602, 0603, 0604, 0606.
•
Yoke, TX202A, open.
•
Yellow and black wires on yoke interchanged.
•
Red and blue wires on yoke interchanged.
•
0801,0802.
•
C8010pen
•
0806,0805.
•
Wiring between boards.
ZBASIC PROGRAM
•
•
Boot up ZBASIC.
Enter the following program:
KEY ON
10 FOR Z= 1 TO 2000
20 PRINT "Z";
30 NEXT Z
40 GOTO 40
• TYPE RUN and press the RETURN key. The
screen will be filled with Z's.
BLACK LEVEL CONTROL
The Black Level control is located behind the front
access panel. Refer to Figure 6-1. Adjust this control
counterclockwise until the raster is visible. Then
back
it
down until the raster just disappears. This
adjustment works best in a darkened room.