HP9100 EHT oscillator transistor

From: Joe <rigdonj_at_intellistar.net>
Date: Mon Dec 21 21:18:59 1998

Tony,

  I have a service manual and parts list for the 9100, I'll try to help.

At 10:53 PM 12/21/98 +0000, you wrote:
>I've got an HP9100 to repair, and the first fault is that the transistor
>on the EHT power supply board

 Do you mean the -3500 Volt power supply board (pn 09100-66522)? That's
the board with the large transformer on it and the focus and intensity
controls.

is short-circut all ways round.
>
>Alas the only number I have for it is the HP custom number, 1854-0322.

   HP says "Q1 -- 1854-0322 -- Quantity 1 --- TSTR: NPN, Si --- (Mfr) 86658
--- obd"

  The notes say that "obd" means "order by description". There's a list of
manufacturer's code in the manual but 86658 isn't listed. ??? I think
those are standard codes, you may be able to look it up elsewhere. I don't
see any other usage for that transitor anywhere else in the 9100 but from
the looks of the circuit, I doubt it's critical. There's a good theory of
operation description of this circuit in the manual. Let me know if you
need a copy.


  Joe


>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).
>
>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.
>
>Does anyone have any suggestions, or has been through this before?
>
>-tony
>
>
Received on Mon Dec 21 1998 - 21:18:59 GMT