Monitor failure when case is on...

[Doug Evans <DE%phoenix.sch.symbolics.com@RELAY.CS.NET>]

    Date: Tue, 23 May 89 14:57 EDT
    From: mkr@philabs.Philips.Com

    OK...I was hoping someone might have had the same problem and knew how to
    fix it...

    Problem:

    When my monitor (a Philips) is fully assembled, it won't work.  I turn on
    the power, I hear the electrons flow 8-), but the screen won't come up, and
    the red LEDs (that normally say FOO at startup) are black.  Every once in
    a while, I'll hear some kind of electrical "pop" (more like a click) and the
    monitor will brighten for half a second, and the red LED's will flash.  The
    sound is not unlike a sudden capacitor discharge, or a static shock.

The power supply is definitely being shorted out somehow and has
shutdown.  What you hear is the supply turning back on to see if the
short condition has been cleared.  Obviously, it hasn't and the supply
shuts down again.

    So, I take the top cover and right side of the monitor off (we just
    gave up our hardware contract, figures) and the thing works like a charm.
    Put the case back on, and the problem reappears.

    The problem is NOT related to temp.

    I tried turning off the light to see if there was some shorting going
    on, but I saw nothing.

You never will ... we use compact switching power supplies in almost all
cases.  These supplies shut down under a short circuit condition before
a spark can be seen.

    If anyone has had this happen to them, and remembers what the prob was,
    I'd be greatful for the info.

    I'm using Genera v7.2  8-)

1    READ THIS:  Do NOT mess with the inside of your monitor unless you are
    confident of your ability to handle LOTS OF VOLTAGE.  BE CAREFUL.

0This ought to be easy ... I assume that since you say it's not heat
related and the problem occurs when you put the covers on, that this is
a mechanical shorting problem.  I mean that if you put the covers on,
the problem occurs immediately, and when you take the covers off, the
problem goes away immediately ... is this correct??

If so, then the problem is that somehow the power supply or its cabling
is being shorted out, shutting down the console power supply.  This can
occur in two ways:

1. Installing the covers shorts a wire to chassis whose insulation might
   have become cut or abraded, baring the wire inside.

   With the console unplugged from walloutlet , carefully (as in
   painstakingly) inspect the console harnessing on the right side and
   around to the rear of the console for any cuts, scrapes or pinches on
   the wiring.

2. The power supply is not properly mounted in the right side of the
   console ... installing the cover allows heat sinks on the power
   supply (which have voltage on them) to come in contact with the cover
   ... shorting the supply out.

   Check the inside of the right cover for telltale scratches in the
   area where the power supply might touch the cover.