curiousmarc

Replacement Siemens LED Chip Arrives

Added 2021-09-12 23:33:29 +0000 UTC

At long last, my hard to find replacement LED chips for the HP 9825 display arrived from the UK, courtesy of her majesty the Queen and eBay UK. They are not the original HP military grade glass on ceramic construction, but HDSP-2000LP compatible chips made by Siemens, presumably under license. There is no tint in the Siemens one, so you can glance at the LED arrays right through the plastic window.

The Siemens devices use a plastic window, a plastic casing and epoxy encapsulation instead of glass and ceramic material, no doubt for cost control. Each LED dot on the matrix is an individual die, instead of the bars of five LEDs that HP used. Which sounds harder to manufacture to me, until you realize that they probably did not want to waste wafer area to make long bars with widely spaced LEDs. Because the plastic window has residual stress and is birefringent, the LEDs appear all colorful and rainbow-y under polarized light microscopy. The IC driver die is covered by a blob of black goop, so you can't really see it.

Compare with the original HP (dead) chip below, imaged right through the red tinted glass.

Both mosaic images were assembled by Ken Shirriff. Thanks Master Ken!

I checked the Siemens chips, they light up, so I should soon have a fully repaired keyboard-display assembly, and best of all, the KDP chip was not dead after all!

Marc