vrs at msn.com
Tue May 13 02:46:05 CDT 2008
From: "Bob Armstrong" <bob at jfcl.com>
> >Vincent Slyngstad wrote:
>>Are you looking to repair a TD8E, specifically? Those look like simple
>> B/!A switches, activated by SDRD and SDRC instructions.
> Yep, I've got a real TD8E to fix that has two bad 8235s on it. Both
> have one output that's stuck low and right now I can't even plug the TD8E
> into the machine - it hangs the OMNIBUS when you do. The board looks nice
> and clean, though, so I'm hoping that's all that's wrong.
> I did a little research and the 74xx TTL family has many AND-OR-INVERT
> type gates (e.g. 7451, 74S64, etc) but even ignoring pinouts and output
> drive capability, none of them are equivalent to the DEC8235. The DEC
> has active low inputs (it's really an "INVERT-AND-OR-INVERT" gate) that
> nobody else seems to have, so replacing 'em with off the shelf parts would
> take at least another chip.
There are enough extra inverters in E01 that I believe you could replace
E05, E10, and E15 with two AS756, an AS757, and the H04 from E01, giving the
same chip count (but much different pinouts). I don't know a source for the
20 pin DIP versions of the AS75x chips offhand, though, and it would still
be a bit of a kludge.
> Does anybody know if the DEC8235 is the same as the National DM8235? I
> don't have a source for the DM8235 either, but at least that sounds easier
> to find. The chips on my board look like they have National logos on
> but they're house marked with the DEC part number. They're also stamped
> "7419", but that's almost certainly a date code - a real 7419 is an
> of some kind.
According to www.nteinc.com, the SN38235N, NE8235L, N8235, N8235N, N8235F,
ECG8235, and NTE8235 are all possibilities. From the datasheets, the
MCC8235, MCC7235, MC7235, and MC8235 are also possibilities. Sourcing any
of them will be challenging, though.
Mouser claims to be able to order NTE8235, but there's no order pending or
delivery date. ($9.09 each.)
I can't find any information on a DM8235.
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