Texas Instruments 990 Manual page 139

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Step Symptom
Table 2-15. Fault Isolation Procedures for CRT Monitor (Continued)
Probable Cause
Sweepboard
Sweepboard
Troubleshooting Procedure
Check vertical output
transistor.
Rotate master brightness
control.
Normal Indication
13 .5 V vertical transistor
collector
Control should allow the
raster brightness to be
varied.
If Abnormal
If zero with flyback
disconnected, check
for 15 V Picofuse
blown or short on
sweep board.
Replace defective
circuit element.