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HP Laserjet IIIP (similar to IIP) Printer Power supply problem


Tony Marsillo

Jan 1, 1970
This printer would power up fine than after 5 min would shut off by itself.
If I turned it off for a few min and turned it back on it would come on
again for a few min than turn off again. It would stay on for less and less
time, until now it will not turn on at all.

Problem seems to be in the power supply itself, switching type. Here is the
info off the supply:

Model#: DPS-85JB
Customer#: RH3-2105
AC Input: 100-120 VAC/4.8A, 45 - 65 HZ
Output: +5V/5A, +12V/0.7A, +24V/1.5A, 69.4 Watts
Date code: 1992-6 Rev A0
Delta Electronics

The HP part number is 33471-69017 which is a RG1-1782.

I checked the caps in the power supply with a Dick Smith ESR meter and found
one with a very high ESR, C6 (1uF/50V) and leaky. Changed it and C152
(1000uF/25V) and C302 (2200uF/35V). Also changed IC101 (TL494).

I am back to the original problem. The printer will come on for two min, and
then turn itself off. I have to turn it off for a few min before it will
turn on again. Never stays on for more than two min. It does not look like a
heat problem; I tried cold spray on various parts in the power supply with
no luck. I touched up any solder joints in the Power supply that did not
look good and checked all diodes and transistors and the FET, all check good
with no power on. Unless something is breaking down under load.

Any help would be appricated.