Fixing 3b1 monitor plug put in upside down

[Bill Mayhew]

The most likely result of plugging the monitor cable into the 3b1
motherboard upside down is blowing out the fuse in the monitor.  If
you are lucky, you may replace the fuse and be back in business.
If not, the monitor is hosed, and it is time to start poking around
at electronic flea markets....

There are several different 3b1 monitors.  Depending on what you
have, there is either a small tubular glass fuse or else a
soldered-in fuse.  The former type of fuse looks like an older
style automotive fuse.  The latter type fuse looks like a 1/8th
watt resistor with a thin plastic skin over it.

Before proceding, heed safety precautions.  Initiate a shutdown
procedure on the 3b1 and park the disk drive with the diagnostic
utility if required.  Good luck on this without the video monitor!
Barring that, treat the system very gently to avoid jarring the
winchester disk heads with subsequent damage to the magnetic
surfaces.

Next, power off the system and unplug it from the wall.  Allow the
system to rest for 20 minutes before attempting repair on the
monitor.  Time is required for any static electric charge on the
CRT to dissipate.  What the static charge may or may not cause a
lethal shock, you could be startled, cause damage to the CRT and
thus risk injury from imploding glass fragments.  Even if the
system has been turned off, you should treat eveything as if it
were still a live circuit, just in case.

There are two screws on the back of the monitor, which when
removed, will allow the back of the case to slide off.  Trace from
where the braided shielded power/signal cable from the motherboard
enters the monitor.  One of the two thickest traces should
eventually lead to the fuse.  Replace clip fuses with units of same
type and rating.  It is probably easiest to piggy-back a new
soldered-in type fuse (of same rating) on top of the old fuse
without removing the old fuse.  Refer work to a person wlith
competent soldering skills.  Check carefully for errant specks of
solder and remove after you finish.  Last, visually inspect the
monitor for dust, foreign objects, etc. before replacing the
cover.

There is apparently no fuse on the motherboard monitor power (12v
from J9), so the monitor itself is the place to look for truouble.
Good luck.


==Bill==
-- 
Bill Mayhew      NEOUCOM Computer Services Department
Rootstown, OH  44272-9995  USA    phone: 216-325-2511
wtm at uhura.neoucom.edu   ....!uunet!aablue!neoucom!wtm
via internet: (140.220.001.001)