We repair a 12.4 GHz Nixie frequency counter plugin, the HP 5255A. It takes a double length episode to get it to behave, and you won't believe what we find at the end.

5245L Repair-a-thon Playlist:    • HP 5245L Repair-a-thon  

My HP 5255A manual high resolution scan:
https://archive.org/details/hp-5255-a...

Further documentation on my website: https://www.curiousmarc.com/instrumen...

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Get more technical info on the companion site: https://www.curiousmarc.com
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00:00 Summary of previous episodes
00:53 The very broken 12.4 GHz plugin
02:19 Operating principle (with elevator music)
06:30 Opening the unit
09:35 Faulty video amp?
12:53 Debugging the Automatic Gain Control
15:48 Debugging the bias
17:32 RF self-oscillation hell!
22:11 Nursing the amp back to life
25:00 Debugging the power meter circuits
32:45 Debugging the gate extender
37:56 Finally measuring microwaves!
39:20 Discovery of another video amp issue
42:12 Debugging the weird low frequency suckout
47:37 Plot twist: RF mixer surprise!
52:22 Did we finally repair it?
55:42 Epilogue: comparing with another plugin