Univac panel and mystery TTL chips

Brent Hilpert hilpert at cs.ubc.ca
Thu Oct 6 16:12:45 CDT 2005


(One possibility would be to look on bitsavers for UNIVAC manual/schematics
from the same period, in the hopes it might list the part numbers you're
looking for.)

(And while it doesn't help much in this case with the ICs soldered in,
house-numbered ICs sometimes have the 'real' part number stamped on the
underside of the IC, sometimes with an apostrophe replacing the prefix, e.g. a
7404 might have on the underside:  '04 , along with some other gobbledy-gook letters.)

If you intend to reverse engineer it I would suggest proceeding to do so, even
without knowing what the unknown ICs are.
Leave the unknown ICs as black boxes in your schematic. There is a high
probabilty you can figure out the function of the unknowns with a little
analysis of the schematic. For the majority of circuits, inputs and outputs can
be identified with the application of a little logic such as:
   - if unknown-pin is connected only to input pins of known devices,
     then unknown-pin must be an output.
   - if unknown-pin is connected (perhaps with inputs on other devices)
     to an output pin of a known device,
     then unknown-pin must be an input.

(The general rule being that one-and-only-one output can drive one-or-more inputs.)

Once the inputs and outputs have been identified a little more observation of
the schematic and the functionality may well be discernable. Of course, keep a
TTL (in this case) reference manual at hand to help correlate pinouts. Some TI
manuals (e.g. TI TTL Data Book/2nd Ed./1981) tend to be good for this because they
have all the pinouts collected within a few pages.

Yes, there are always exceptions to the above such as open-collector or
tri-state circuits, paralleled buffers, some devices may not be 7400 series:
perhaps specialised IC or 75000 series interface IC, etc., but considering the
nature of what you are dealing with (a front panel, in which you already have a
lot of known inputs & outputs (switch & lamps), along with known ICs), I'd say
your chances of figuring everything out are good.

Sometimes one can be mislead when a connection to a pin is actually just a
'way' for the trace, but considering the fineness of the PCB traces, that may
be less likely to be an issue in this instance that it is on earlier boards.

It all makes for a rather fun puzzle actually, once you get past the tedium of
tracing traces.

(Qualification for making such a suggestion: Not to toot my own horn too much,
but just so you know I'm not blowing wind and suggesting 'Oh, it could in
principle be done like this', I have reverse engineered entire machines (mostly
early calculators) containing up to 250 SSI/MSI ICs, and in which all the
ICs were black-boxes (no info or cross-reference available), and managed to
produce the complete logic schematic, followed by successfully building a
logic-gate-level simulation of the machine, which, for the most part, 'proves'
the schematic.) (e.g. http://www.cs.ubc.ca/~hilpert/eec/ics/M5300.html)


"J. Peterson" wrote:
> 
> Hi,
> 
> I have a control panel from a Univac mainframe that I hope to re-animate
> someday.  Unfortunately I know very little about Univac mainframes.
> 
> First I'll go for broke: does anybody recognize this unit and have
> schematics for it?
> 
> http://www.saccade.com/writing/projects/UnivacPanel/UnivacPanel.html
> 
> No?  OK, time for plan B, reverse engineering it.  Most of the chips on the
> panel are straightforward 74xxx TTL, however, a number of them appear to
> have a seven digit part number instead of a regular 74xxx stamp. Is there a
> translation guide between this seven digit number and regular 74xxx
> numbers?  Most of the 74xxx parts on the board also have these seven digit
> numbers.
> 
> Any tips on how to guess the actual function would be most appreciated.
> 
> Thanks,
> John Peterson
> www.saccade.com



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