"BperryB" wrote in message
ups.com...
A neighbor gave me a little Coleman 400 watt power inverter to try and
repair and I found 2 of the MOSFETS bad and one of the driver
transistors controlling the upper side of the bridge shorted. Replaced
the bad parts and got it working with a small 25 watt light as a load.

Unfortunately it failed again with same symtoms when installed in his
motor home and connected to a 13 inch TV set. As it failed, the fault
light and beeper came on indicating a fault and the input voltage was
only 10 volts. I assume the fault was due to too much drop in the long
wires. But it was too late to shut it off. The unit continued to
indicate a fault after the load was removed.

Is this one of the usual failure modes where the input is too low to
support the output? I would think the unit should be protected from
overloads and low voltage, but apperently it fails easily when the
battery voltage is too low? Also I don't know if a battery charger was
attached to the battery or what condition the battery was in. The
connection at the unit read 12.3 volts with no load and 10 volts after
it failed. i don't know how much current was being drawn after it
failed.

This thing is only worth about $40 and I see them on sale at Harbor
Freight for $19.99 so it's probably not worth spending too much time
on. If he buys another unit, what brand would you recommend for long
life and ruggedness? Something more expensive perhaps?

Do not waste any more time (unless you enjoy troubleshooting). Tell him to
replace it and select one with better specs (if the size and cost are not a
problem).