by Mike, W8CM

 About once a year, I get to travel to a repeater site to find out why it is off the air.  Invariably, when I get there I find out that there had been a ‘glitch’ in the 110 Volt AC power that had caused the system’s Astron 12 Volt DC power supply to shut down.  After the system then used up the backup battery’s charge, the Low Voltage Disconnect circuit had done its duty and turned off the repeater to prevent any damage to the battery and/or transmission of poor quality signals on the air by the radio.

 Now, don’t get me wrong; the Astron linear-regulated power supply is a very popular unit, works well, and is economical.  It also has a VERY effective and fast acting internal protection circuit.  Once this circuit has triggered and shut down the output voltage, it is normally reset by flipping the power switch off for a couple seconds and turning it back on.  When this happens, the Astron happily acts normally with regulated output voltage.

 The only thing is, these things never happen at a convenient moment. Not to mention that during storms it would be nice if the power supply did not decide to turn itself off and the repeater system did not have to go on battery.  What to do?  Gee, it would be nice if I could be like the Yellow Sheets and “let my fingers do the walking” so the protection circuit would be reset without having to drive to the repeater site.  Here’s where the good folks at Astron get their gold star and merit badge: they have come up with an inexpensive and easy solution.  I found out about this while reading through the web side www.repeater-builder.com

 You can build the circuit yourself, or for only $20 you can have Astron sell you one of their fully assembled printed circuit boards of the Over Voltage Protection Reset - 12volt (OVPR-12V).  You won’t find this in any Astron or ham dealer catalog; you have to know it is available. I bought several units directly from the Astron factory, but you might find other sources with a web search under that part number.  I’ve installed this device into several Astron linear power supplies now, and it’s like having an automatic transmission in my car; (1) glitch comes in, (2) power supply shuts down the output voltage, then (3) OVPR-12 resets the power supply to normal output voltage, and this all happens in the blink of an eye. 

Installation is easy, as Astron provides clearly detailed written and illustrated instructions. The OVPR-12V pc board is mounted using an existing internal filter capacitor clamp’s hardware and then four color-coded wires are soldered to the power supply regulator board.  Of course, don’t forget to UNPLUG the AC cord while working inside the power supply!  It is also a good idea to wait a little while after turning off the power supply, as those filter capacitors can hold a nice charge (read that, big spark!) after the AC is turned off.

 The OVPR-12V is a product of
The Astron Corporation  

Irvine, California 92618
949-458-7277

 Circuit and parts needed for Astron OVPR-12V

1N4148 is a general purpose switching diode; 1uF capacitor is tantalum; resistors ¼ or ½ watt, transistors are 2N3904 general purpose npn

 Where to connect wires on Astron regulator p.c.b.: