HP 2100A Restoration

Bob Rosenbloom bobalan at sbcglobal.net
Tue Aug 2 00:11:17 CDT 2016

On 8/1/2016 6:29 PM, Hayden Kroepfl wrote:
> Hi,
> I recently acquired a pair of HP 2100A minicomputers locally for very
> cheap. Don't think I could get much more local that a guy literally at the
> end of my street. He bought them at an auction over ten years ago, never
> powered them on, and left them in his garage since. They've likely never
> been powered up since they were last in regular use. The units seem to be
> complete, apart from missing a few I/O cards that are written onto the top
> of the power supply. I don't plan to power them up until I've taken them
> apart, cleaned all the dirt and debris from them, and inspected the power
> supply.
> With regards to the power supply, I'm thinking my best bet would be to do a
> power on with no cards in the system. Though I'm not sure if all the power
> rails would even come up without a load on it, since it sounds like it may
> do some power sequencing from what I've read. I was wondering if anyone has
> some experience with testing a similar power supply that hasn't been run in
> at least 10 years?
> I'm not sure if using a variac to slowly warm up the supply and the caps
> would be wise on one of these power supplies. I'm not sure how the
> switching supplies would handle the low voltage at the start.
> The only I/O card that was installed in both machines, besides a terminator
> board in only one of them, is a serial interface made by some company with
> the logo CMC. It uses a COM2502 UART which I was surprised to find a
> datasheet for, however I haven't found any information on the card itself.
> I have a photo of the card in the album linked below if anyone has any
> information on it.
> I know this email is getting a bit long, but with regards to the memory
> both machines have a ID(16K) driver board, and two core modules. However
> one machine has both core modules marked 02100-60052 on the bridge, and the
> other has one marked 02100-60052 and the other 02100-60054. Is there any
> difference between these modules? I'd assume by the 16K driver in both,
> that all of the core modules are 8KW modules. Would that just be a later
> revision or is one a different size?
> I've taken some photos of the machines and put them here:
> https://goo.gl/photos/z2tGBbNvekwrxS5L9
> I'll be taking more after I make some space to start taking the units apart
> for cleaning and inspection. I've also included photos of the serial
> numbers and other badges on the backs if anyone knows of a resource to
> decode them.
> I'd very much appreciate any help or suggestions that people have. I really
> want to get at least one of these machines back into full working order to
> have some fun programming with.
> Thanks,
> Hayden K.

It's a low frequency, 800Hz IIRC, switcher so don't use a Variac and do 
have a load.

There's a separate manual for the power supply: 
(from bitsavers). It has everything you need.

There's a bunch of small electrolytic capacitors on the Inhibit Driver 
Load Card, A106, that needed to be reformed before my memory would work 
They reformed themselves in one of my units. I had memory errors for an 
hour or so then they went away. On other units, I reformed the caps 
(took the board
out and slowly brought it up on a bench supply), and had no memory 
errors at first power up of the system.


Vintage computers and electronics

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