Since both units are now completely functional, it's time to rip 'em apart, rebuild the power supplies, clean, and paint...

But opening things this old up always reveals more work to be done that you didn't plan on. For example, the plastic socket at the neck of this CRT was (very) loose and starting to crack. We can't source a new socket, so liberal use of High Tech Adhesive™ will fix it in place permanently.

The underside of the main board has even more components on it. They all look OK.

Here are the (burned out) incandescent display stack label backlights. Decades of heat from these bulbs has warped the plastic film with the actual labels on it, and burned away or faded some of the black backing. This has been repaired and replacing these bulbs with LEDs will remove the heat issue. Care has been taken to preserve the original bulb sockets so that future collectors could replace the LEDs with bulbs again, although it's likely that even micro-incandescents like this will be illegal in our dystopian future.

The power supply has what appears to be a half-wave rectifier with capacitor-smoothed output. These two dinky diodes tested OK, but you know? They just look weeny and unsuitable for a Real Man's Calculator, which the 9100 definitely is. (And what? Couldn't HP afford two more diodes for full wave rectification? But so much of the 9100's operation seems to depend on electrical things we'd call "side effects" these days that it's probably unwise to functionally revise anything...)

There! Much better. To those who might complain that this was completely unnecessary, I simply retort that Art is always misunderstood by the hoi-polloi...

My motto: "if it ain't broke don't fix it"

So except for the fix of the register names backlight, I would just leave the rest alone.

Did you measure the Vf of the original diodes? For all we know you may have replaced low Vf grmanium diodes with higher Vf silicon parts. (OK, just pure speculation. But again, why replace something that works.)

Each to his own, hope it still works when you put it all back together

And... have fun :-)

Very nice!

By the way, the stock rectifier *is* full-wave. A half-wave rectifier uses only one diode. Two more would make for a bridge rectifier. Just an FYI.
-Adam

Great writeup, Dave! After seeing your old TI at HHC2011 and having the delightful experience of meeting you and your wife, your postings are appreciated even more.

"Our dystopian future" indeed!

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By the way, the stock rectifier *is* full-wave. A half-wave rectifier uses only one diode. Two more would make for a bridge rectifier. Just an FYI.

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Duh! Of course you're right. Just goes to show I should stick to programming rather than trying to explain what Atherton's doing to my machines...because I can solder largish parts I shouldn't think I'm a hardware guy!

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But again, why replace something that works.)

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Because it looks better.

Granted, nobody will ever see it. But still. Think of it as the bevelled and polished gears in an expensive mechanical watch that nobody but the watchmaker will ever see...

Thanks Jim...

Beautiful pics. Are you planning on making a website documenting the restoration?

Dave

My wife keeps telling me I should do a web site for my whole collection. That would take weeks. On the other hand she's probably right...and a section on the 9100 restoration would make for interesting reading...

Since I host and run my own servers it wouldn't be hard, just tedious.

Really very nice and clean work. They must be happy to have found a home like yours :-)

BTW and FYI, I know "the hoi-polloi" (a bit redundant, isn't it?) as ho-ochlos ;-)

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There! Much better. To those who might complain that this was completely unnecessary, I simply retort that Art is always misunderstood by the hoi-polloi...

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I suppose the rest of the world has eventually caught up with
the electronic manufacturing finesse of HP (and to be fair
perhaps others such as Tektronics, etc..). Yet it did take
several decades to close that gap.

I recall on the occasions I've needed to prod internals of HP
equipment in the mid 80s, I simply didn't want to close it back
up. It was by any measure manufacturing elevated to an art form
far more worthy for display as a wall hanging rather than
suffocating in ABS.

Looks like a fun project BTW. ;)

That's the only design flaw in the 9100: it should have had a transparent package.
Joel