Re: {Collins} KWM-2A blows fuses upon power up

----- Original Message ----- From: "W4FID - John Wiley" <W4FID@xxxxxxxxxx>
To: "CCA e-mail list" <collins@xxxxxxxxxxxxx>
Sent: Monday, February 06, 2012 1:32 PM
Subject: {Collins} KWM-2A blows fuses upon power up


After working beautifully for almost 2 years my 2A developed a problem. No "decline" or reason to suspect trouble. Then as I was tuning up it took out the 5A slow blow fuse on the variac.

Apparently whatever shorted did a thorough job as the outlet on the variac is now dead. It was a Chinese variac and I can take it apart or just replace it easily enough when I get a chance. I liked the idea of using the variac switch instead of the function switch on the 2A to power the rig up/down and I brought the line up from about 95 volts to 115 gradually (maybe over about a minute) when I powered up and then down gradually to about 95 volts when I powered down. That part of the problem is manageable.

I plugged the 2A into an outlet direct to test it. But when I switch it on there is a hum and the dial lights for about a second -- or two at most -- then the fuse on the 516F-2 blows.

I have no bench; no test equipment; and limited knowledge. Any ideas where to start looking for something obvious or anyone in north central Florida (+/- a couple hundred miles of Ocala) who is able/willing to take on the repairs? I'll bring the rig as I drive well -- just don't fix stuff too well.

If you have suggestions please reply via the list so others can benefit. If you're up for a repair job please contact me directly.

John  W4FID

Not having any instruments or tools makes it very difficult. I suggest at least finding a multi-meter at a Radio Shack. They are not expensive and will allow you to do simple tests like measuring the resistance at tube sockets to see if they are the same as in the charts in the handbook. A simple ohmmeter can also find shorted capacitors and diodes although you may have to lift one lead. A small soldering iron would also be useful, again a suitable one is available at Radio Shack for not very much. You can do about as much power supply trouble shooting with a cheap VOM and a few tools as with much more elaborate equipment. If the rectifier is a vacuum tube take it out of the socket and bring up the voltage slowly. If the main fuse blows or if the transformer growls at lower voltage its an indication that there is a short somewhere else, perhaps the transformer.

Richard Knoppow
Los Angeles

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