Univac panel and mystery TTL chips

Tony Duell ard at p850ug1.demon.co.uk
Thu Oct 6 14:14:52 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.)

HP were often particularly kind about this, their manuals, if they 
contained full parts lists, did give the equivalents. Alas most HP 
desktop computer and calculator manuals are boardswapper guides, but...

> 
> (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 all else fails, I've even been known to desolder the IC to firstly 
look at the underside, secondly to look at the PCB (I once found the 
normal uumber in the silk-screen under the IC -- this was in a device 
where all the IC numbers had been sanded off to keep me guessing for at 
least 5 minutes!), and thirdly to test the IC on a breadboard.

> 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

Even if like me, you've got the common TTL pinouts hard-wired into your 
brain :-)

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

Having done this to a fair few devices, I would agree with you.

> 
> (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

The most complicated calcualtor I ever did only contained 8 ICs. And 
those only had 8 pins each. What made it interesting were the several 
hundred transistors, the thousand-or-so diodes, core memory, 
core-on-a-rope ROM, and a PCB ROM. No, I haven't extracted the contents 
of the ROMs yet.... (HP9100B if you're wondering).

Fortunately, for the later HP desktops, I had the equivalents list, so 
most of the non-custom ICs were known. Figuring out details of the custom 
parts was one interesting bit. As, of course, was working out how the 
whole machine was supposed to work. 

-tony




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