Tuesday, August 30, 2016

Fixing My Astron Power Supply

Some time ago I posted about fixing the front-end of my FT-897 tranceiver which had gone deaf on 6 meters.  I've gotten a number of comments and emails from folks thanking me for supplying those details -- they were able to get their rigs fixed as well.

In that spirit, here's a report of my latest equipment fix.  I have two Astron power supplies for the shack, an RS-35M (the one with the meters) and a RS-35A (with no meters.)  The 35M powers the main rigs, transverters, and accessories.

The 35A was slated to power various VHF and UHF power amplifiers as I bring them on-line.  I bought it used and it started to have problems almost right away. It came up with the correct voltage on the output and could supply a little bit of current (it could run an FT-897 on receive) but as soon as a significant load appears (the FT-897 on transmit) its would cut power.

A little on-line discussion and snooping indicated that it was probably the SCR/crowbar board.  Well, I didn't have a lot of time to horse around with this, so I decided to go for the low-hanging fruit.  I ordered a couple of LM723CNs off of EBay (for a whopping $0.99 shipped!).  This past Saturday I pulled off the cover, removed two bolts holding down that crowbar circuit PCB, and swapped out the LM723 -- happily it's socketed (circled in red).  Screwed the PCB back down, turned on the power supply and Presto!  It's able to put out full current now without tripping the crowbar circuit.

Now THAT's the kind of fix I like -- three minutes of my time and $0.99 of my money.  I hope this helps somebody else get an Astron power supply back in play.


  1. thanks for the 2M Qs in the Sept. VHF contest. - N0JK

  2. Hey, thank you too Jon! That was a long haul on 2 meters! Hope to catch you in the Sprint this coming Monday.