14 Apr
2008
14 Apr
'08
3:24 p.m.
Rik wrote:
Is that _always_ the case? I think I've seen a Tandon TM100 drive where
the logic board is identical in layout and circuitry to a standard one,
but is gold-plated (like most HP boards of the time), has an HP part
number in the etch and 1820-xxxx chips on it. I would be very suprised if
HP made that board themselves.
The PSU isn't build by HP but by RTE
POWER/MATE a firm with doesn't exist
any more.
That explains it. If HP bought the PSU as an assembly, there wouldn't
be HP part numbers for its components, as it would be considered a single
FRU. From Tony's schematic, I'd guess that
it's a semi-custom part. Motorola
probably binned one of their standard parts
to a higher spec for RTE.
Perhaps you can look at schematics for other switching PSUs
with similar ratings and determine what transistor they use. The
safety-critical parameters are breakdown voltage and maximum current.
Too low a current gain may mean the transistor operates in the linear
part of its chracteristic, and promptly overheats.
If the PSU is rated at less than 500W, I suspect you
could use a BU208A,
which costs less than $3 from Digikey, but don't take my word for it.
I am almost sure it's less than 500W. It's quite a small supply.
A BU208A is a good suggestion. As is a 2SC1942. And there are many
others. The problem is it gets expensive if one fials after another. And
you don't know if they're failing becuase they're unsuitable or because
the original fault, the one that caused the original transistor to fail,
is still there.
-tony