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fusing links

Posted: 18 Feb 2020, 07:09
by Fonotec
The Display Processor board in the LS-76 has four DIL-16 PROM (programmable, read-only memory) chips made by Signetics, that are of the fuse-link variety, for conversion of the feed voltages, digitized-as-8-bits-per-word, binary, into base-ten Arabic numeral display from the 7-segment, red l.e.d. indicators for the control panel's LPI readout (as shown also in the thread in this forum titled, '2668-B PC').
400_LPI_detail.jpg (35.21 KiB) Viewed 270 times
The PROM chips originally shipped from Signetics, blank, having all outputs at logical LOW. L. J. Scully would have to program them by applying a high voltage to certain pins which would fuse a Ni-Cr (nickel-chromium) link internally that would convert the given output to a logical HIGH state. By using the DATA I/0 model 29B, I was able to clone the four unique PROMs from the Eva - Tone LS-76 (#660) (used as master devices) to four NOS N82S126 PROMs (target blank devices) so that the Display Processor board from the Nigerian LS-76 (#662) would have working PROMs and so that there would be inventory for #660 and #656 in the future.
PROM_COPY.jpg (336.94 KiB) Viewed 275 times
If you have an LS-76 and need PROMs, we can help. We have more blank PROMs and the fuse-link process with the vintage 29B is confirmed to be successful (as of 18-2-2020), when we tested its results in the Display Processor board of #660 (shown, below).

LS-76THELATHE660.jpg (861.38 KiB) Viewed 275 times