Dead EEPROM Dumped With Help Of Body Diodes [Hackaday]

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[Jason P], evidently an enjoyer of old reliable laser printing tech, spilled a drink (nitter) onto his Panasonic KX-P5400 SideWriter. After cleanup, everything worked fine — except that the PSU’s 5 V became 6.5 V during the accident, and the EEPROM with LocalTalk interface firmware died, connection between VCC and GND seemingly interrupted inside the chip. Understandably, [Jason] went on Twitter, admitted the error of his ways, and sheepishly asked around for EEPROM dumps.

Instead, [Manawyrm] wondered — would the chip have anti-ESD body diodes from GND to IO pins, by any chance? A diode mode multimeter check confirmed, yes! It was time for an outlandish attempt to recover the firmware. [Manawyrm] proposed that [Jason] connect all output pins but one to 5 V, powering the EEPROM through the internal VCC-connected body diodes – reading the flash one bit at a time and then, combining eight dumps into a single image.

After preparing a TL866 setup, one hour of work and some PHP scripting later, the operation was a success. Apparently, in certain kinds of cases, dead EEPROMs might still tell their tales! It’s not quite clear what happened here. The bond wires looked fine, so who knows where the connection got interrupted – but we can’t deny the success of the recovery operation! Need a primer on dumping EEPROMs that are not dead? Here you go.

Here’s a cool trick to recover data from a broken/defective EEPROM after an overvoltage or reverse-power event:

Misuse the internal ESD protection diodes to feed the chip with voltage through the data pins. Then take multiple dumps with different bits being powered. https://t.co/WHUiiaJdgf

— Manawyrm (@Manawyrm) August 26, 2022

We thank [Chaos] for sharing this with us!