Troubleshooting HP 2116B

Christian Corti cc at
Mon Jul 30 10:33:28 CDT 2018

On Sat, 28 Jul 2018, GerardCJAT wrote:
> Christian,
> I absolutly agree with David s post.
> Back in the ' '70 when I was maintaining 3 x HP 2116 B running 24/24 7/7 
> FOR around 10 YEARS, the ONLY memory related problem that I got was 
> traced to a faulty transistor !!

Then I have a new fault ;-)
After swapping the transistors with those for bit 16 (parity, not used in 
this machine), the fault was still there. Swapping the IC did not help.
Finally, I found it: one of the two 1.65k resistors going to the 
outputs was bad (open). These are the collector resistors for the 
differential amplifier.
So if I had found that resistor earlier the board would look a bit nicer 
than now; it is not easy at all to desolder those little 8 pin metal cans.

There was a short electrolytic on one inhibit driver card, but that was 
fixed several days ago. This fault was obvious: the PSU was shutting off 
with the card in its slot.

Now to the flakey bit in the other memory half. Perhaps the corresponding 
resistor on the other card starts to go bad?


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