Astron Revitalization (Part 1)

..don't let the title fool you. The revitalization was occasioned by stupidity on my part. I was trying to modify a perfectly fine Astron RS-20A to facilitate gel cell charging. I installed one of those nifty Chinese LCD Volt/Amp/Watt panel meters to monitor the charging process of gel cells. When they are down, I put 'em on and -- even in a severely discharged state -- they top right up by drawing about 500-600 mA at first and then the current dwindles as they reach a charged voltage of about 13.5 volts nominally. The important thing is they are not left on interminably to cook. They get yanked when the current gets consistently below 100 mA in about 6-8 hours.

Well, I had done the mods and was testing it with several batteries around the shack when tragedy struck! I reversed polarized one and zapped something because the PS terminal voltage dropped to about 9-10 volts. So, going into debug mode, I did some poking around and put together a description of the problem to be posted on the Repeater Builder Yahoo Group. Herewith is my initial plea. (Note that I turned these into images to preserve the spacing that the HTML interpreter kills.)

Before we go any further, the Repeater Builder site (not the Yahoo Group) has a wealth of articles on R&R of these beasts. If you are in the same hell I was in, click on the links and read further:

• Repairing Astron 13.8V Linear Power Supplies
• Trouble Shooting an Astron Linear Power Supply
• Crowbar SCR Usage in Astron Linear Regulated Power Supplies
• LM723 Regulator Operation in Astron Linear Power Supplies

These aren't the only ones. There are many others that offer a treasure trove of knowledge. If you do as I have done, you will become pretty adroit at understanding and repairing these. Not an expert but good enough to spot a PS at a swap meet labeled "parts or repair", pick it up for $5, and have it running in no time with just a few inexpensive parts.

The main article was Repairing Astron 13.8V Linear Power Supplies by WA1MIK. It works its way from the wall socket to the binding posts and helps you trouble shoot by symptom. (Mine was "low voltage".) I reduced the main part of the article to a sort of checklist:

Going through the above, I thought that it drove me pretty convincingly to the regulator board as being the problem -- and that everything else was just dandy! Boy what a mistake that was!

Stay tuned..