TRS-80 Model 1 Expansion Interface question?

Win Heagy wheagy at
Mon Mar 20 19:46:31 CDT 2017

I have a clean, and somewhat functional expansion interface that I just
tested over the weekend.  Without the EI connected, the model 1 reports
~16K RAM and with the EI the model 1 reports ~48K, so the RAM seems OK.
But, the FD1771 IC, for some reason, was removed from an otherwise
apparently functional EI.

Is there any reason why this chip would be removed?  I see a number of them
on ebay for around $25.  The expansion interface hardware manual indicates
it is an FD1771B-01, but the service manual indicates a couple
possibilities....FD1771 A/B -01 -11.  Any considerations to look for here?



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