HP9100 EHT oscillator transistor

From: Geoff Roberts <geoffrob_at_stmarks.pp.catholic.edu.au>
Date: Mon Dec 21 20:45:18 1998

-----Original Message-----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
Date: Tuesday, 22 December 1998 10:32
Subject: HP9100 EHT oscillator transistor

>I've got an HP9100 to repair, and the first fault is that the transistor
>on the EHT power supply board is short-circut all ways round.
>Alas the only number I have for it is the HP custom number, 1854-0322.
>Tests on the transistor in my (working) 9100 show it's an NPN transistor,
>but I don't want to do too many tests on it in case I damage the working
>I've tried a few modern replacements. Most of them oscillate OK, but the
>EHT won't regulate and sits at far too high a voltage (small, bright
>image on the CRT).

Certainly indicative of high eht.>

>A BF259 does seem to work, but it's hardly got sufficient ratings for
>this circuit. I don't know how long it will last.

What voltages are on the transistor in the working unit?
What sort of package is the transistor in?


Geoff Roberts
Computer Systems Manager
Saint Marks College
Port Pirie South Australia.
My ICQ# is 1970476
Ph. 61-411-623-978 (Mobile)
      61-8-8633-0619 (Home)
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Received on Mon Dec 21 1998 - 20:45:18 GMT

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