Identifying mystery TI ICs (Motorola MDP-1000 investigation continues...)

[Josh Dersch]

On Sun, Oct 4, 2020 at 10:26 AM Brent Hilpert via cctalk <
cctalk at classiccmp.org> wrote:

> On 2020-Oct-04, at 1:22 AM, Josh Dersch via cctalk wrote:
>
> > More mysteries while poking at the MDP-1000.  Spent some time this
> evening
> > working out the rest of the signals on the power harness (I suspect
> inputs
> > for an LTC circuit and a "power good" signal, as well as something
> > connected to a relay on the backplane, probably related to power
> control).
> >
> > There are a lot of unidentifiable ICs on the main CPU logic board and on
> > the backplane, mixed in with bog-standard 7400-series TTL.  Curious if
> > anyone has any ideas, as my searches and perusal of datasheets/databooks
> on
> > Bitsavers have turned up nothing.  These are all TI-manufactured ICs,
> 1969
> > manufacturing dates, with "SN48xx" and "SN63xx" part numbers (a few omit
> > the "SN" prefix.)  I'm wondering if these are just standard 7400 ICs with
> > special codes; for example there are several SN4816's near the edge
> > connector for the I/O bus, where a 7416 might (?) make sense, and from
> some
> > basic probing and following traces I think the pinouts make sense.
> > (Everything's conformal coated so it's a real bear to beep things out...)
> >
> > Any ideas?
>
> I have run across TI ICs from that era with odd/unknown series numbering,
> in particular the SN3900 and SN4500 DTL ICs.
> Notably:
>         - by pinout they match up with standard DTL series ICs,
>         - I have only found these in equipment from one manufacturer:
> calculators built by Canon.
>
> I received a solitary page of datasheet for some of them (by way of a
> Canon service center many years ago), but I have never seen them mentioned
> in TI databooks from the era, even in those sections where they list e.g.
> "other products from TI" and proceed to list little known series and part
> numbers.
>
> So an obvious guess is these were house numbering systems of standard
> parts done for the purchaser/equipment manufacturer but with TI's format
> scheme rather than a format specified by the manufacturer. Another guess
> would be standard parts tested and selected for purchaser-specified
> parameters, although that seems a little excessive for these cases.
>

Yeah, either of those options seems a likely possibility.  It definitely
seems like they were building this thing for bulletproof operation, so
maybe it really is the latter.


>
> The 54/7400 series originated with TI in 65, I'm not aware of them
> producing any other TTL series, other than perhaps second-sourcing some
> other manufacturer's.
> I guess that's another possibility - another manuf's TTL series, labeled
> differently.
>
> Odd that this Motorola CPU is filled with ICs manufactured by TI.
>

Yeah, the irony of this was not lost on me.  Other than the aforementioned
linear ICs in the core modules, every IC in this has a TI logo on it.


>
> It's conceivable, although it seems less probable, that they're DTL rather
> than TTL.
>
> On the whole, best guess would seem to be 7400-series inside.
>

Yeah, I'm guessing (hoping) 7400 as well, especially since there are actual
74xx-labeled ICs in here casually mixed with the 48xx and 63xx.

A thought occurred, that if I get desperate I could remove a few of the ICs
and attempt identification using the IC tester I have.  Not going to do
that unless I can't figure it out any other way.  The good news is there
aren't too many varieties.  I haven't done a full inventory but there's not
more than a dozen or so different types in here.


>
> --
>
> On another issue, did you trace the +/-15V lines to the core
> address/inhibit drivers?
> Could some of the remaining wires from the PS be other core supplies - 15V
> was a little low compared to most core systems I've seen.
>
>
I did manage to trace the +/-15V lines to the drivers on the core memory.
I don't believe any of the extra signals are other voltages -- three of
them go to the CPU board, one goes to the aforementioned mystery relay, one
goes to a tiny bit of logic on the mainboard (I suspect some manner of
LTC), and the last goes to a trace that just dead-ends and goes nowhere at
all.  The very little documentation I have on the CPU itself suggests that
the supply provided only +5 and +/-15.  There are two sets of power rails
for each; the first goes to the CPU, front panel, and two memory slots, the
second set goes to the other two memory slots.  I suspect that upgrading
past 8K of memory required a power supply upgrade.

- Josh