scary warning about bubble memory loop mask, TI 763/765 maint manual

Eric Smith spacewar at
Sat Aug 5 20:29:00 CDT 2017

Al just put the TI Silent 700 Model 763/765 maintenance manual up on
Bitsavers. (Thanks Al!)

The 763 and 765 are the models using internal bubble memory for between
10,000 and 80,000 characters of local storage.  They use either one or two
"discrete memory boards", with one 92 Kbit bubble device each, or one to
four "dual memory boards", each with two 92 Kbit devices.

Bubble memory devices typically have many minor loops, not all of which are
usable.  TI printed mask data on the label of the bubble device,
identifying the defective loops.  When a bubble memory board is installed
or replaced in the terminal, it is necessary to put the terminal into
command mode and issue a test command to enter the mask.

The scary part is this warning in section


    Care should be exercised in the installation of the bubble memory
    mask. If an incorrect mask is entered, the bubble device will not work
    correctly even if the correct mask is entered at a later time. If an
    incorrect mask is entered, replacement memory board must be
    installed because the bubble device is no longer reliable.

Intel provided the necessary technical information and hardware to recover
corrupted bubble devices in the field.  As far as I can tell, TI did not.

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