Univac panel and mystery TTL chips

[Tony Duell]

> 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 

A number of manufacturers used house-coded ICs like this. HP are the 
best-known (the 1820-xxxx numbers), but ICL, Xerox and I believe IBM did 
it too. The main reason for this, apparently was that any IC with that 
house code would work in the circuit. So there might be one number for a 
generic 7493 and another for a specifically TI 7493 (I think that's the 
chip were the TI one has a slight difference to others). TO have the 
house code simplified manufacturing.


> 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.

Well, with ICs marked with both, you can start to make the equivalents 
list. If you are very lucky that will identify a few more ICs on the board.

> 
> Any tips on how to guess the actual function would be most appreciated.

Well, you can find the power connections, right? If you are lucky, there 
will be a few ICs with odd power connections (i.e. not the corner pins) 
which will be a start.

Then you might be abloe to identify some pins as definite inputs (driven 
from totem-pole outputs on known ICs), others as definite outputs (only 
go to known inputs). 

If all else fails you may have to desoler the IC, power it up on a 
breadboard, find outputs with a logic probe, try the inputs, and so on.

-tony