Sunday, October 13, 2019

First Signs of Life

Last week, while troubleshooting the power supply in my amplifier, I discovered there were blown out diodes in two places.  The board I was working on contained two power supplies and both of them had their bridge rectifiers blown out.  Getting replacements required an order from one of the parts suppliers who will sell small quantities (Mouser, in this case) and getting a few of each part (two is one...). The parts came Friday and I spent some time checking out everything else on the circuit board to check if it looked like it wouldn't blow out the diodes again. 

After getting the nerve to solder down parts and try it, my amplifier powered on today.  This marks the first time it has successfully turned on since the lightning strike August 1st.  The last time I'm sure it was on would have been early to mid-July.  See those green LEDs on the top box?  That's the first sign of life. 

Posing on the top of the replacement antenna rotator controller.  The replacement rotator went up two weeks ago (end of September). 

I rush to add that I'm not out of the woods.  I'm not even sure I can see the end of the woods from here - but I'm not entirely sure of anything in this box.  The power supply board I fixed contains two low voltage supplies.  One of those is converted to 45 Volts for the power amplifier.  Assuming the 45V is supposed to be on whenever the amplifier is enabled (bottom left switch on the black triangular box on top), something in that chain is dead.  I get no voltage on the 45V output terminals.

Getting this to turn on is a positive first step, but only a first step.  Still, it's the most encouraging thing in the fight with this damaged amplifier so far, so I'm stoked about it.


  1. Is this a linear or switching supply? I forget which Icom amp you have. I figured the surge might have clobbered the rectifiers, so good job!

    Not dumping all the breakers on the circuit is a good start. Here's hoping there aren't any damaged "proprietary parts" left to be found.

    1. Switchers. Secret hint: the amp model is in the picture.

      So far, I've gone through three sets of those two 4A fuses I showed, and two of the 20A breakers on the back panel, but these two bridges are the only parts I've found that were actually blown by the surge.

    2. I should add one of the switchers (the smaller one) used a single chip, 3-pin, analog regulator for one of its outputs. Bizarre one, too: a 78M18. I've never seen that voltage in one of those chips.

    3. Ahhh...a PW-1. Nice amp. I know you can get the 78-series of regulators in many voltages. Don't know if I've seen an 18 Volt one, but I'm not surprised they make them.

  2. Hum filter at the output of the rectifier? Should be a series element, possibly a ceramic resistor but ideally an inductor, straddled by two sizeable capacitors going to ground. If the capacitors were shorted you would already have smoked the new rectifier, but perhaps the series element opened in the original event.
    Not a ham, but fiddled with AN/FRT-XX's for a few years, back in the day.

  3. "That's right buddy, you show that turd who's boss!" - Tom Arnold, Austin Powers: International Man Of Mystery

    Stick with it, man.


  4. When troubleshooting power supplies that refuse to cooperate, and keep popping fuses, For troubleshooting in place of glass fuses I jumper in a circuit breaker appropriately sized in place of the fuse. Such circuit breakers are a few bucks each and cheaper than a box of 3AG fuses. And a variac is good to slowly bring up the primary voltage before things avalanche and allow the smoke to escape from the solid state devices and resistors. I have always wondered how the manufacturers manage to put all that smoke is such small parts. And the smell will get the wifey going for a while.