21 Dec
1998
21 Dec
'98
3:45 p.m.
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
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
transistor.
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?
Cheers
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)
61-8-8633-8834 (Work-Direct)
61-8-8633-0104 (Fax)