[vcf-midatlantic] Univac, our first real work!

Evan Koblentz evan at snarc.net
Mon Jun 13 16:01:59 EDT 2016

Hey everyone,

Our workshop this past weekend had the usual highlights -- we repaired 
all sorts of 8-bit stuff, monitors, did some programming, enjoyed plenty 
of nerdly shenanigans -- but by far the highlight was when Duane C. and 
Bill Drom. told me the Univac 1532 I/O console (paper tape + Model 35 
teletype) was ready for its first power up!

Background: We acquired a complete-ish Univac 1219-B mainframe about six 
years ago. One tape drive was on display for a few years in our old 
museum, and much of the full system was on display as one of the VCF 
East shows, but mostly the computer lived in our warehouse. That changed 
this spring when we opened the new museum: its double doorway enabled us 
to put the computer on permanent public display. We cleaned it on the 

Bill Drom. and Duane, who both used this model of Univac in their Navy 
days, jointly approached me ahead of this past workshop and asked if 
they could start technical work by modifying one of the console units 
for a modern power supply. They assured me it's safe and easily 
reversible to the original configuration, so I said yes.

A summary from Duane about what they actually did:

 >> The +/- 15 and -4.5 switching supplies fit in the space we removed 
the 400 Hz. transformer-diode assembly. The -28 volt supply wound up in 
the air channel at the bottom. We bypassed the 400 Hz. power on relay 
and have to turn on with a external switch. Does anyone have a feel of 
what 60 Hz. voltage would pick a 115 Volt 400 Hz. relay? if it is a 
straight inductance problem it would be 17.25 volts . We left that for a 
future visit when we have a variac to play with. We did not have time to 
trouble shoot all the problems the 1532 had. at first the logic was so 
crazy that we put in a logic drawer from another unit. turns out the 
display unit was missing cards. The rubber on the reader capstan had 
turned to a gooey mess and peeled off onto the tape we tried. If none of 
their consoles has a usable pinch roller they will have to send it off 
to a service that does that sort of thing. Maybe we could try some of 
the liquid rubber that is made to dip tool handles in. The punch is 
punching extra bits. The oil on the TTY was all dried up and at first 
the TTY would not do anything. It took about an hour of oiling and 
moving stuff by hand until it gradually came to life. The tape chute has 
the bracket that holds it up under the punch broken so the tape gets 
snarled coming out of the punch. It will be easier to swap out the tape 
drawer than to try to swap the chute. I put in a new one once and it 
took me about a hour to figure out how to get it in without bending it. <<

Saturday night, when only the power supply was installed, about a 
half-dozen of us went into the museum room and observed the first 
power-up. Here's the video... well actually it's take two; the first 
time I idiotically recorded it with my phone in portrait mode. :)


We have three more of these console units in storage, along with one 
extra CPU and one extra tape drive, which is all very helpful for 

This is an exciting milestone for us! I'm going to send a note to the 
nice people who gave us the system as well.

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