Unknown transistor repairing a TI990/5 power supply

Chuck Guzis cclist at sydex.com
Thu Apr 28 12:34:30 CDT 2016

On 04/28/2016 02:45 AM, Alberto Rubinelli - Fondazione Museo del
Computer wrote:
> I'm working at the power supply of a 990/5 minicomputer. The chassis
> is a 6 slot version, with 20A power supply. After a few minutes of
> working, the fuse blow and I found a transistor on the main power
> supply board with collector in short circuit with emitter. The
> transistor has TRW logo and is market with Texas part number
> 996070-003, in addiction with the date code.

I don't have a magic key to translate the house part number to something
real, but if I were to guess, based on the location of the transistor, I
suspect it's an NPN high frequency device.  A good guess would be that a
"universal" TV horizontal output transistor might be a good candidate.
I've done that myself to old PSUs and it's worked well.

Try, say, an NTE238 or 2SC1308K or similar.


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