Re: TED based motherboard

From: Ethan Dicks (
Date: 2007-03-28 03:16:45

On 3/27/07, Anders Carlsson <> wrote:
> Bil Herd on behalf of Jeri Ellsworth wrote:
> > The two resistors on the chip mark it as a TED where the test mode pins
> > were higher impedance than predicted by the chip designers and a strong
> > electric field would freeze the counters.
> Oh, those are resistors? With my limited electronical knowledge, I really
> thought they were diodes too.

Those really look like two diodes to me - glass, orange with a black
band... diodes will act a bit like resistors in the sense that there
is a voltage drop across a diode junction, but they are not like
resistors in all cases - you'd have to look at the spec sheets and
know (or measure) the current in circuit to calculate how it will

> Bil writes that he added an 8-bit latch "8529 or something like that",

Lots of MOS parts are in the 85xx family.

> while I observe two chips named 8329, assumed to be RAM. Ethan suggested
> that U4 should hold a 82S100 or similar.

I would suggest that the RAM chips are from the 29th week of 1983, not
that they have a part number of 8329.  Given that the board is stamped
Aug, 1983, the dates on the RAM chips seems reasonable.  I would think
that the DRAMs are known as IMS 2629P-15, for "INMOS" and P for
plastic package, and 15 for 150ns.

The 2629 isn't an obvious part number, but Inmos has a 2620 and a 2630
in the right size range...  It's certainly not as
common a part as a TI4416, but there were plenty of by-4 DRAMs after

> I need to get access to an EPROM reader/burner to dump those chips
> safely. The 2764:s I could read off a C64 cartridge with EPROM slots,
> but I don't think I have anything to read the 27128.

If you have anything with a 27256 socket, the 27128 is like that with
one less address line.



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