Table of Contents
Advertisement
The A3A3 Line Generator Assembly converts the digital X and Y display positions from the
Digital Storage processor to analog values and draws lines between them. It positions the
characters with respect to the graticule and sets the size of the display and graticule.
A distorted CRT display involving both the horizontal and the vertical components is often
caused by malfunctions on this assembly. If only the video information is distorted, suspect
the A3A8 Analog Digital Converter. Drawing of the characters is controlled by the Character
Stroke Memory on the A3A4 Memory Assembly.
If both the X and Y channels are distorted, suspect the Expand Register @, Reference 0,
Long Line Switch Driver @ and/or the INTG or SMPL control signals, as these are common
to both channels.
If the positive amplitude at A3A3TPll is only $2 V, the gate of either Q5 or QlO has been
damaged.
The Long Line switches Q7 and QS can be tested as follows. Set A3A2R12 in the LL position
(full CW). A3A3TP6 is then a TTL low and the gates of Q7 and QS are approximately
-15 V. With A3A2R12 in the fully CCW position, A3A3TP6 is a TTL high and the gates of
Q7 and QS are approximately -1 V.
If it is determined that any of the Sample and Hold FETs Ql through Q4 or Q12 through
which FET is defective.
The Digital Storage Test Programs can be used to troubleshoot the analog functions on A3A3.
When using these programs, the LL/SL pot A3A2R12 should be set to the full CW position
(LL). The SL (full CCW) position should also be examined as it exercises the circuitry at the
highest speeds.
Digital Storage Test Program 5 and the CRT display are used to verify the input Registers
and the DACs. It is not necessary to remove A3Al when testing A3A3. The display in Figure
4 is the result of a Y DAC or Y Register malfunction. Notice that the malfunction causes
vertical jumps in the test waveform. A defective component in the X channel would cause
horizontal jumps.
6 A3A3
Advertisement
Table of Contents
