HP 5335A repair and upgrade

[@joelkist6493]

Nice find and fix...

[@SoddingaboutSi]

I have various vintage electronic test gear, hp 8662a ,8568a and other Marconi gear. If I don't use them for a year or so they are always troublesome. You video has just reminded me to power up the signal gen and spectrum analyzer. Thanks for your upload.

[@andymouse]

great video....cheers.

[@davidv1289]

Another interesting video, thank you! Get a copy of HP Service Note 5335A-26B - this service note details replacement of the fan with a 24 Vdc unit and re-wiring of the power control relay to use two sets of contacts (pins 9 & 10 as well as pins 11 & 12) to switch the + 5 volt supply (the fan power is switched directly by the front panel mechanical switch). I used an emb/papst model 8394 fan. If you need to replace the relay socket the part number is 27E213 (Digikey P/N PB806-ND or Mouser P/N 655-27E213). For the firmware upgrade I used AT28C64 EEPROMS and made an adapter to use 28 pin SOIC chips in the original sockets. They can be programmed with any of the modern programmers and work just fine. Also, make sure you get the firmware that matches your Channel C prescalar (there are two) - otherwise your Channel C frequency values will be incorrect. Finally, next time you have the counter connected try slowing the gate time to more than 10 seconds and watch the display - surprise!!!!

[@mymessylab]

Thanks for all your suggestions. I’ll try it for the surprise!

[@xufocom]

micro Hertz - not nano!

[@mymessylab]

Yes, you are right! Sorry