


July 1, 1986


Brian Lees
Modern Power Conversion Inc.
7100 Warden Ave. Unit 3
Markham, Ontario, Canada  L3R 2L6


Robert Briody
Integrated Solutions Inc.
1140 Ringwood Ct.
San Jose, CA  95131


Dear Mr. Lees;

The 500 watt power supply (MPC 301A-010-S157) ran for approximately 60 hours
on our dynamic load test fixture before failing. The output was pulsed between
51.7 amps and 98.9 amps at an 8 second repetition rate (4 seconds @ 52 amps and
4 seconds @ 99 amps). The sense lines comprised of a twisted pair of wires and
were terminated at the first 50 amp load. When we discovered the supply had
failed, the supply was unplugged from the AC line. The DC voltage was measured
across the 60 Hz AC bridge rectifier. The DC voltage measured 150 VDC after 
the supply had been unplugged for approx. 1 minute. This leads me to believe 
that either the PWM control IC failed or the MOSFETs failed. The supply had 
approx. 70 CFM of forced air cooling. The ambient room temperature was approx.
23 degrees Centigrade.

Enclosed you will find a schematic to our dynamic load test fixture. Also when
we received the supply, one of the large resevoir capacitors (C5 ?) was loose.
Please repair, if possible, as we wouldn't want the capacitor to vibrate loose
during shipment.

From our initial testing of the supply, we are very excited about having a
500 watt power supply in such a compact package. We will be glad to work with
MPC in evaluating and failure analysis of the 500 watt supply. We look forward
to using the supply in our V24 minicomputer system.






Sincerely,



Robert Briody
Design Engineer


