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 Repairathon Playlist:    • HP 5245L Repairathon  

Documentation on my website: https://www.curiousmarc.com/instrumen...

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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