Focus Adjustment; Power Supply Adjustment Procedures - IBM 3278 Series Maintenance Information

6. For Model 5 only:
a. Set the display to 132-character-width mode_
For this test the Normal/Test must be in
the Normal position and the 3278 must be
connected to a properly customized 3274.
See step 21 of Test Mode 3 in paragraph
3.3.1.3; use normal cursor.
b. Adjust the height and width potentiometers
(Figure 4-6) to screen size as shown on the
alignment mask.
7. With the intensity control fully clockwise (and
released) and the raster blanking potentiometer
fully counterclockwise, is the background
raster visible? If so adjust the raster blanking
potentiometer clockwise to just blank out the
raster lines_ With the intensity control fully
counterclockwise, no display should be visible.
Set the intensity control for readability. With
the contrast control fully clockwise, the con-
trast between the high-intensity and normal-
intensity fields is maximum. The normal-
intensity fields may not display if intensity is
set at a low level. Set the contrast control for
readability.
5.3 Focus Adjustment
The focus potentiometer is located on the high-
voltage power supply (see Figure 5-1). Adjust the
focus potentiometer for the best overall definition
of the screen image characters at the center and
those at the edge of the display area.
5.4 +44 V Power Supply Adjustment Procedures
To adjust the +44 V power supply to the correct
operating range (+44 to +48 V), perform the
following steps.
A. Preparation
1. Switch off the 3278.
2. Connect the jumper to pin J6 on the low-
voltage power supply. (See Figure 4-11.)
3. Switch on the 3278.
B. First Measurement
1. Measure the voltage at fuse 5 (+) to dc return
(-J.
2. If the voltage is between +44 and +48 V the
adjustment is completed. Skip the following steps.
5-4
SY27-2510-6