7.10. How can the monitor fail?
[Courtesy of Rob Stampfli:]
I have witnessed the loss of more than a few Unix-PC monitors
to a phenomenon where the right side of the screen becomes
increasingly compressed (nonlinear), at an exponentially increasing
rate, until the monitor fails completely. Usually, this occurs over a
period of months, and it usually is observed after the monitor has
been removed from service, stored, then placed back into service.
[Rob notes a particular case which was diagnosed by his
colleague, Harry Maddox, BEFORE the monitor failed completely. He
writes, "We believe that an actual failed monitor would take out an
associated transistor and the flyback transformer, unless the monitor
is fused, presenting a much more difficult problem to fix." The
A 4.7 uF 25V non-polarizing electrolytic capacitor (C411) is
bad. C411 develops a high internal resistance and gets quite hot,
which further causes it to deteriorate. It may explode -- use
caution. C411 is located between L402 and T401 inside the monitor
proper. The value and voltage rating of this capacitor is not
critical, "ESR" [equivalent series resistance] is however.
Replace C411 with a mylar capacitor, 4-6 uF @ 25V or more,
such as AT&T 535GA (4.22 uF @ 100V) or equivalent. Mount on end with
insulation on top lead. Dress away from adjacent parts.
Replace CAP ASAP before further damage is done. Replace fuse
if blown. Check TR402 for Collector to Base shorts if set was not
working. Also D403 for short.
1. Remove CRT Cover (2 screws in back).
2. Remove Speaker Assembly (2 screws).
3. Remove RF Tape from bottom cover (shield). One tape is
hidden at front of bottom shield.
4. Remove bottom shield.
5. A small part (I think a thermal sensor) is found on the
bottom of the PC board just under C411. It is covered with
black tape. Remove the tape and bend sensor out of the
6. Remove C411 and replace with Mylar capacitor, 4-6 uF, 100V.
7. Replace sensor and tape.
8. Reassemble monitor.
Note: the bottom shield is tricky to remove and replace if you
don't unmount the monitor from its swivel mount, but it can be done.
If monitor has failed completely, then check fuse (if present), TR402
(C-B short), and D403 for a short.
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