HP9100A wake-up in 2021

[PaoloB]

Today I had enough spare time to test my HP9100A that was idle since about > 5 years.
I expected that a long storage time could result in a faulty unit so I was ready to bad news, indeed at power-on there was no display !

Anyway the registers indicator backlight was on so that at least the low voltage power supply was OK. I checked the three fuses first, all ok (the HV one was a bit suspect, like having some accrection along the thin wire but was ok on a ohm-check).
I was suspecting some oxidation of contacts so I gently moved up down the two HV boards around the CRT and the board protruding from the power supply case in the aim to break oxide layers if any.

After these manipulations the next power-on was OK, the three register 0's showed on the display after some 20 seconds: all ok with the CRT and related power supply then.

I went along with a few manual calculations, (sum, multiply, trigs) all ok.
I then input (manually) the 9100A test program (from the service manual), checked it line-by-line via the STEP-PRGM key editing a few mistakes and then run it: all OK, the three registers blinked their correct Z=1. ; Y=2.000 ; X=3. around three seconds.

I then recorded the test program onto a magnetic card.
I erased the RAM program using another magnetic card which fills the whole memory with STOP (code 41).
I used the newly recorded magnetic card to reload the test program and run it: all ok.

As a first conclusion I could say that all the basic functionalities are OK after the long storage, I took a log for these in view of a future re-check when it could happen.

In 2021 this machine is now over 50 years old, I was wondering that it is likely that this was the only HP9100A in function today in the whole world.

I add a few pictures as a record of the feat.