CuriousMarc | HP 5245L Nixie Counter - Part 6: HP 5255A 12.4 GHz Plugin Repair @CuriousMarc | Uploaded 1 year ago | Updated 2 days ago
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: youtube.com/playlist?list=PL-_93BVApb5_MQBUOVLgdKCaUPY1zaPh_

My HP 5255A manual high resolution scan:
archive.org/details/hp-5255-a-frequency-converter-operating-and-service-manual-05255-9022-may-1967

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

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- Amazon links for the tools I use in the lab (supports the channel if you buy from there)
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Get more technical info on the companion site: 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