Uploaded March 2024 | Updated September 2026, 2 weeks ago

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We repair a classic HP 3478A 5-½ digit voltmeter, and admire its ultra complicated A to D converter.

HP Multislope II ADC patent: patents.google.com/patent/US4357600A/en

Ian Scott Johnston video on HP 3457 backlight mod: youtu.be/oEu7nqOkKxo

Blacklight display mod: eevblog.com/forum/testgear/another-hp3478a-backlight-display-hack

LCD protocol reverse engineering: eevblog.com/forum/projects/led-display-for-hp-3457a-multimeter-i-did-it-)/msg1347268/#msg1347268

OLED mod: eevblog.com/forum/testgear/hp3548-hp3457-oled-display

Ken Shirriff's Nanoprocessor reverse engineering: righto.com/2020/09/hp-nanoprocessor-part-ii-reverse.html

Ken Shirriff’s reverse engineering of the hybrid in Marco Reps’ HP 3458: https://x.com/kenshirriff/status/1448392567167479812?s=61&t=UXfboHQEfahjAKeGVe1J8w

Jeff Peletz amazing HP instrument pictures: hparchive.com/wallpaper

Stuff that supports the channel:
- Amazon links for the tools I use in the lab: curiousmarc.com/amazon-links
- Channel merch on Fourthwall: curiousmarc-shop.fourthwall.com
- Legacy channel merch on Teespring (I don't have everything transferred to Fourthwall yet): teespring.com/stores/curiousmarcs-store
- Support us on Patreon: patreon.com/curiousmarc

"Elevator Music" Credit: Crinoline Dreams by Kevin MacLeod

Our lovely sponsors
- PCBWay: fast turn PCBs, pcbway.com
- Electro-Rent: electrorent.com
- Keysight: test instruments: keysight.com
- Samtec: connectors: samtec.com
- R&D Microwaves: rdmicrowaves.com

Get more technical info on the companion site: curiousmarc.com
Contact info: youtube.com/curiousmarc/about