On 27/05/2013 19:19, Brent Hilpert wrote:
  On 2013 May 26, at 4:38 PM, Josh Dersch wrote:
  I've started looking at what it's going
to take to get the memory in
 the Imlac running again. There are two core assemblies in this
 machineand they're both in pretty bad shape as they were exposed to
 moisture for a long enough period that they accumulated quite a bitof
 corrosion on the control logic.  (The cores themselves seem to be OK).
 I went over the better of the two assembliesand cleaned the legs of
 every socketed IC.  In the course of doing so I found maybe 10 chips
 with legs that were falling off. I took alook at a random sampling of
 chips from the worse of the two assemblies and every single one of
 them has legs that are corroded through.  So I'm going to be
 replacing a lot of chipsif I want to get these running again.
 Most of these are 7400-series logicand aren't hard to find. However,
 there a set of components that I'm not too familiar withand I'm not
 having much luck finding replacements. Now that I have the schematic
 I at least know what they are(had no luck looking them up based on
 the labels on the chips), they're described as "Transformer, 60uH",
 "Transformer, 6uH" and "Transformer, Square Loop" and have part
 numbers of 517A0024, 517A0023, and 517A0021.
 The chips themselves that are in my machine are labeled as follows
 (for the 60uH variant):
 14201
 NPIPA-2581
 <date code>
 These are in 16-pin DIP packages. I'm going to need to replace quite
 a few of them.
 Any ideas of a modern replacement? (Any idea where to source NOS or
 used ones?) I can provide pictures if that'll help. 
 I have a large scrap core memory driver/interface board with a
 quantity of 8 and 16 pin pulse transformers on it (dual and quad packs):
 2624-7486
 NPI
 NP-5163
 7912H
 and
 2624-7429
 NPI
 NP-3142
 7846H
 The 2624- numbers appear to be Burroughs house numbers as I think the
 board is from a Burroughs machine, the 79xx/78xx date codes.
 I wonder if NPI was the transformer manufacturer. I RE'd the board so
 I do have a schematic that shows how they are used but don't know
 anything about their specs beyond that. 
It looks like they are the Manufacturers.
http://www.trademarkia.com/npi-73366630.html
and some product here:-
http://www.electronicsurplus.com/Item/3274-1.jpg
but it looks like the company is long since dead.
 As I suggest in another message, another possibility might be to
 investigate ethernet-isolation transformers. 
Whats special about Core Memory Transformers that means generic pulse
transformers can't be substituted? Aren't they there to detect the sense
pulse...
Dave