HP 5245L Nixie Counter - Part 1: The King of 1960s Frequency Meters

We start repairing our very broken HP 5245L. It is arguably the king of the Nixie frequency meters of the 1960s. Equipped with the right plug in, it could count up to 18 GHz. Many of them were used in the Apollo communication ground stations. But this digital instrument does not use a single IC: it's all made with individual transistors inside! It feels like repairing a giant IC, but with access to every transistor. We're sure not complaining about it. 5245L Repair-a-thon Playlist: https://www.youtube.com/playlist?list=PL-_93BVApb5_MQBUOVLgdKCaUPY1zaPh_ Documentation on my website: https://www.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) https://www.curiousmarc.com/amazon-links - Channel merch on Teespring: https://teespring.com/stores/curiousmarcs-store - Support us on Patreon: https://www.patreon.com/curiousmarc Our lovely sponsors - PCBWay: fast turn PCBs, https://www.pcbway.com - Electro-Rent: https://www.electrorent.com - Keysight: test instruments: https://www.keysight.com - Samtec: connectors: https://www.samtec.com - R&D Microwaves: https://rdmicrowaves.com Get more technical info on the companion site: https://www.curiousmarc.com Contact info: https://www.youtube.com/curiousmarc/about 00:00 The HP 5245L, king of 1960s counters 02:06 HP instruments at an Apollo tracking station 03:19 Looking inside and first turn on 06:04 Power supply check 06:30 Crystal oscillator check 08:58 Backplane and previous failed repairs 10:22 10 MHz Multiplier repair 12:25 Board A35 Time Base Repair 15:24 Board A19 Input checkout 16:41 Board A21 Function Control checkout 19:17 Board A21 repair 25:28 The differentiator works! 26:27 Gate signal fault 27:14 Summary of Episode 1 repairs