Thorny diagnostic issue for an Epson QX-10 - test-drb@ccmp.vtda.org

17 Apr 2013

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 Symptom: A QX-10 keeps shutting down, but at random and in an erratic way.
 By erratic it will sometimes shutdown--Start---Shutdown--start---within a
 1/2 second of each sequence.

 It sounds like there is a short somewhere or at least some component
 failing.  But where?   Its hard to diagnose because (1) It's intermittent
 and (2) I don't want to run the machine when it's flip flopping on and off.
  That's definitely not good for the components.

 I've determined that it's either the PSU or mainboard at fault.  Both are
 for sale on e-Bay.  However, I don't whant to buy both when only one is the
 problem.

 Any ideas how I might determine which?  The PSU doesn't not fire at all if
 there is no load on it.

I've never seen an Epson QX-10 - I don't even know what it is.

Whatever it is, one way to approach it is to make a dummy load for the PSU
which resembles the normal load on it as far as possible.  If the PSU continues
to malfunction when feeding only the dummy load, the problem is almost certain
to be in the PSU itself.  Dummy loads for low voltages can often be made from
bulbs for use in cars, including dual filament bulbs which had to be replaced
because one filament failed.

Another useful thing to do is to look for bad connections in the PSU.  If it is
constructed on a printed circuit board, while feeding the dummy load, try
examining the underside of the board in a darkened room while tapping the board
with something insulated.  You might see or hear tiny sparks indicating the
location of a bad solder joint.

Be aware that the PSU probably contains high voltages and that these may
remain for a considerable period of time after power has been removed,
particularly if the unit is faulty.

Regards,
Peter Coghlan.