Uploaded May 2023 | Updated September 2026, 2 weeks ago

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We continue repairing our very broken HP 5245L, and hit some really subtle bugs in this amazing all-transistor machine. Opening the Nixie decoder to reveal its many neons and photo-resistor tree is a special treat.

5245L Repair-a-thon Playlist: youtube.com/playlist?list=PL-_93BVApb5_MQBUOVLgdKCaUPY1zaPh_

Documentation on my website: curiousmarc.com/instruments/hp-5245l-nixie-counter#h.ixw2jz3t1jtb

Stuff that supports the channel:
- Amazon links for the tools I use in the lab (supports the channel if you buy from there)
curiousmarc.com/amazon-links
- Channel merch on Teespring: teespring.com/stores/curiousmarcs-store
- Support us on Patreon: patreon.com/curiousmarc

Our lovely sponsors
- PCBWay: fast turn PCBs, pcbway.com
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- 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

00:00 Summary of previous episode
01:16 Board A21 gate signal repair
04:10 Why is it still not counting?
06:31 Board A17 fast counter repair
11:19 Still not counting right
12:28 Board A15 counter/display explanation
14:20 Taking apart the Nixie decoder
16:25 Board A15 counter neon bulb debug
19:22 Reset issue discovery
20:48 Nixie decoder reassembly and test
21:56 Board A23 reset debug
23:39 Reset fault cured
25:48 Repaired!