Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!super!udel!rochester!cornell!mailrus!ames!lll-tis!lll-winken!scooter!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.sys.amiga
Subject: Re: 1084s goes poof. Film at 11.
Message-ID: <1378@neoucom.UUCP>
Date: 26 Oct 88 03:07:47 GMT
Article-I.D.: neoucom.1378
References: <8097@gryphon.CTS.COM>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 54


Although our two model 1080 monitors do not crackle, the problem
seems to be endemic for other owners.

Most of the failed monitors that I've run across have gone south to
to a nonpolar electrolyic capacitor drying out and shorting in the
horizontal output transistor's collector coupling to the horizontal
output transformer.

It seems that certain far eastern manufactuers scrimp on the
quality of said capacitors.  The capacitors' dielectric paste seems
to dry out (I'll bet its warmer inside the monitors than the parts
are spec'ed for).  When the past dries out, the capacitors short.
The shorted caps sometimes go fizzz-pow!; other times, they quietly
blow a fuse inside the monitor.

It comes to mind that the voltage being supplied to the monitor
might be too high.  Only experienced people should do go sticking
wires into wall sockets.  It might not be a bad idea to have the
voltage measured.  At one time my office was located near a large
air handler.  The air handler caused the voltage to sag on its
feed, while the voltage in my office being on the other phase rose.
I was getting 140 volts.  Light bulbs didn't last very long, but
everything else seemed to tolerate it.  A different office I was in
was aslo beset with poor power, and the ground lead was about 25
volts with respect to the frame of the building.  We found out when
a maintenance guy went to drill a hole and got a BIG spark when the
bit touched a metal beam in the wall.  At yet another place I
worked, there was an ethernet cable that went between buildings,
that was bonded to the frame of one building, but had about 40
volts AC on it with respect to the case of the server in the other
building.  Fortunately, the cable taps have ground isiolation.
Ground wires with voltages on them can be caused by a variety of
faults.  Sometimes some equipment will loose its neutral lead,
dumping current into the ground, this may cause a voltage drop
through the ground lead.  Also a delta-wye transformer without the
Y side bonded can let the ground float.

The point I was trying to get at is that just because power comes
from edison, it is not necessarily good power.  If your neighbor is
an energy pig, and you are supplied from the same distribution
transformer, it can mess up your voltage.

There are some spark-gap capacitors in most monitors that are
supposed to discharge to ground when conditions are out of bounds.
It seems plausible that if one's ground wire was not zero volts,
the spark gap capacitors might discharge more than they should.
I'd be tempted to test or have someone else test that the neutral
(white) wire to ground is approximately zero volts, while the hot
(black) wire to ground is not more than 120 volts.

If the voltage is OK, than it might just be a case of bad luck.


--Bill