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Fingerburner tip. The 7254 uses no protection

A project log for Magnetic Bubble Memory Makes a Comeback

An Old Attraction to Magnetic Bubble Memory leads to a 1Mbit Board for the SBC-85, 8085 based single board computer

CraigCraig 04/10/2020 at 16:210 Comments

To learn more about the system and what errors it will detect and report, I am looking at waveforms and playing with the system under various configurations. 

Not completely unrelated, the simplified diagram for the Intel 7254 drive transistor bridges that run the X and Y coils in the 7110 bubble looks like this---

If you ever wondered to yourself "Does the 7254 have pull downs on the gates that keep the FETs from floating ON which would result in the chip shorting itself from +12V to ground and therefore burning itself up?"  Well, the answer is no. 

Note to self--- The 7254 has nothing to keep the gates from floating on.  Never run the 7254 without the pre-coil drive 7250 in place.  I don't know if this set still works, but I doubt they are still a matched pair as when new and now the tip of my finger smells like a combination of melting plastic and burnt flesh.  I am glad they were a recovered set and not my good chips.

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