Tag Archives: power supply

This is a post of semi-random electronic carnage.

This is some plastic that went between the metal case and the circuit board.  The two things sitting on it are capacitors.  It appears they went off like bottle rockets.

This is some plastic that went between the metal case and the circuit board. The two things sitting on it are capacitors. It appears they went off like bottle rockets.

The high-voltage area of the power supply.  This is where the failure occurred.  Note the charring.

The high-voltage area of the power supply. This is where the failure occurred. Note the charring.

This is the top of the power supply.  Some of the caps are definitely exploded.

This is the top of the power supply. Some of the caps are definitely exploded.

This is the low voltage area of the power supply.  There isn't much visible damage here.

This is the low voltage area of the power supply. There isn't much visible damage here.

This is the grounding bolt.  Note the burn marks.

This is the grounding bolt. Note the burn marks.

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Category: Equipment

Last summer, a friend brought me an Astron RS-35 Power Supply to repair.  It had been involved in a near-lightning-strike experience that fried the loading coil on an antenna, among other things.  The problem was that as soon as the supply was switched on, it would blow the fuse.  The only thing that was obvious was that something was causing the SCR crowbar circuit to fire and blow the fuse to save the power supply.

I started out by checking the bridge diodes and filter capacitors.  All seemed fine.  I checked the pass transistors and those were fine.  During a last resort, I removed an electrolytic capacitor and replaced it with another of the same value, but less voltage.  My hope was that the voltage on the original capacitor was unnecessary, or that I would have enough time to test a few things before it blew.

Of course, it never happens that way.  I had about 15 seconds (not enough time) before letting the magic smoke out of the capacitor.  So, since I'm not an electrical engineer, I decided to run a few tests on the blown cap.  I noticed that there was no physical damage to the capacitor EXCEPT a small hole in the jacket.

So after staring a little at the schematic (there is an awesome resource on the Repeater Builder website), I decided to remove a capacitor (C6 on the schematic image below).  It seemed like a likely possibility, since this was part of the SCR firing circuit (the part I circled in orange highlighter).

Low and behold, it was it!  I replaced the part with a new one, and the power supply is done!

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Category: Equipment

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