HP 9825 insane LED display chip (Patreon)

All the LED chips that make the beautiful 32 character display line in my HP 9825 are dead! They died from the 13V overvoltage. These chips, capable of displaying 4 characters, each a matrix of 5x7 dots, were specifically developed for the HP 9825. HP sold them later commercially, under the HDSP-2000 series.

They are amazing and probably insanely costly hybrids on ceramic, containing 28 bars of LEDs, stitch bonded to form 4 arrays, and 2 driver IC chips, under a cover of tinted glass.

The chip in the middle is a shift register, so you can load 28 bits for a row of all characters serially, then display that, then move to the next row. 

Ken Shirriff reversed engineered the driver chip already and explains how it works on twitter:

https://twitter.com/kenshirriff/status/1431752029106409473 

I'll be showing a short video of the bits dancing around the shift register as I test the chips in the next post. 

Marc