Texas Instruments 990 Manual page 136

Table 2-15. Fault Isolation Procedures for CRTMonitor
~
Step Symptom Probable Cause Troubleshooting Procedure Normal Indication If Abnormal
\0
+:-.
Any fault with
CRT, sweepboard,
Vt
+:-.
symbol form yoke, or flyback
N
+:-.
I
\0
• Video dim Sweepboard Check socket at base of tube Normal bright video in Replace defective
-..J
0
for tightness and intermittent contrast to raster eleme:nt (socket
-
connection. Isolate fault to assembly or sweep-
sweepboard by replacement. board! component).
CRT (tube) Check for internal arcing, or Rephtce defective
broken or missing pins on tube.
base.
• Poor geometry Linearity sleeve Adjust horizontal linearity No distortion Check yoke or sweep-
(raster shape) placement sleeve for optimum hofi.· board!.
t-..> zontal character linearity
w
(if applicable).
~
Linearity sleeve Move ground (copper foil) No distortion Readjust linearii:y
ground strap to another area on Aqua.dag. sleeve:.
placement
Yoke Look for missing pincushion No distortion Replace yoke or
magnets and attempt to glue in appropriate
correct with additional magnet(s).
magnets.
Fly back Isolate to flyback by No distortion Replace flyback.
0
replacement.
<9:
~
CRT
(J)
Isolate to CRT tube. No distortion Replalce tube.
"<
(I)
Symbols not
sam~:
Yoke assembly Adjust linearity sleeve Symbol size - 66 dots Replalce yoke
01
(i)
•
3
size across screen under yoke (if
applicable~).
per inch, ± 7 dots CRT tube.
(I)
0
<·
rn·
a·
~