Upon the date 03:07 PM 8/6/00 -0400, Kevin Schoedel said something like:
>On 2000/08/06 at 12:19pm -0400, Christian Fandt wrote:
>>However, during a production day, that old "A" developed a shorted
>>series-pass transistor in its switching PSU board which put ~+18 volts onto
>>the +5 V supply bus. Well, you know what happened next. I recall very well
>>the HP Service Manager down at the old Paramus, NJ Service Center grousing
>>that this happened occasionally and that those %$_at_*)! designers did not put
>>in a crowbar circuit or other protection to prevent smoking the whole
>>machine.
>
>Is there a straightforward fix for this? I'm not up to tracing out the
>supply and developing one myself, but I could follow instructions if
>someone else has done this already.
There is, believe it or not, a "service manual" for the 9825. I had the
company buy one back in the mid-80's. Heckuva poor excuse for a service
manual, but at least it has the PSU board schematics in it. No other
schems, just PSU. I wonder if this was because the PSU had proven to be a
fairly unreliable module?
I have basically zero spare time anymore it seems (I should be doing one of
several rather important things right now instead of typing this, however
I'm a bit loyal to the group), but probably the practical solution would be
to build a simple crowbar circuit out of an SCR and a few passive
components and hang it across the output of that pass transistor. I feel an
appropriate time delay fuse should be put inline between the rectifier and
pass transistor too. Reason for that is the PC board traces could be fried
before the main fuse blows. I could excavate my library for the manual
(well, it's _somewhere_ upstairs in that very full room :-), scan the
circuit and squirt it out to somebody who's got time to perfect this. Tony?
>
>>Regarding the comment by someone in this thread (at 8:08 AM, 3 Aug as shown
>>above), what makes the replacement kybd so horrible?
>
>The keys tend to bind unless they are pressed exactly in the center and
>exactly in line with the stroke, and they bottom out hard.
>
>>Could that have been
>>an early version of a replacement before the Cherry's were used?
>
>I don't think this one is a *replacement* keyboard -- the date stamped on
>the keyboard (22 Aug 1979) is earlier than the date on the bottom of the
>case (5 Feb 1980). There is no obvious sign that the keyboard was made by
>anyone other than HP; the PCB is marked on the top upper left corner with
> [(hp)] 88809F REV A 5021-1416
Interesting. You said this was an 'A' model? Maybe by the time I had to
replace the repaired chicklet keyboard on our old A, Cherrys came into use.
I do recall both the Paramus serv. manager and our local CE as exhibiting
pleasure at the replacement being a Cherry as if it being Cherry was the
tonic to end all ills.
Regards, Chris
-- --
Christian Fandt, Electronic/Electrical Historian
Jamestown, NY USA cfandt_at_netsync.net
Member of Antique Wireless Association
URL:
http://www.antiquewireless.org/
Received on Sun Aug 06 2000 - 20:45:09 BST