Upon the date 02:03 AM 8/7/00 +0100, Tony Duell said something like:
>Those 'chicklet' HP keyboards are a pain to dismantle. Not only because
>there are around 100 self-tapping screws on the back, but also because
>the keys _will_ fall out. Never take one apart, no matter how careful you
>think you are, without making a digram of the key positions. If that
>sounds like the voice of experience, you're right!.
>
>Put the keyboard face-down on a flat surface so that all the keycaps are
>supported and then take off the PCB.
I had all the manuals for the 9825's which include several closeups of the
complete keyboard. So, having that safety net, I was fearless in this
endeavor. Many of you don't have manuals so Tony's suggestion of spending
the extra time to map the keytop locations will pay well in the end. Just
take your sweet time and relax as you're dismantling and reassembling, all
the while focusing on the locations of the parts.
>
>
>> 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 9815 PSU (and I guess the 9825) has this as a failure mode :-(. It's
>not pleasant.
>
>Has anyone ever tried adding a crowbar to these supplies? It shouldn't be
>hard to add a fuse in series with the input to the switching regulator
>and the SCR/zener/resistor circuit from the +5V line to ground, but would
>it do any good?
As I recall the HP service manager's comment while we were chatting about
the problem: a crowbar can be better than what already exists.
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 Mon Aug 07 2000 - 19:23:01 BST