Tag Archives: w2aew

I decided to build a Colpitts oscillator after watching one of W2AEW's videos.

Circuit Board

Circuit Board

Frequency Counter

Frequency Counter

Waveform on the scope

Waveform on the scope

The only issue I ran into was that I had the power supply hooked up backwards, so when I initially connected it to the scope, the +12V shorted to ground (and it burned a small hookup wire in the process).  I should have paid more attention to the testing that W2AEW describes in his video - on a second try, I was seeing -7V where I should have been seeing +5V.  And I shouldn't have trusted the two hookup wires I was using to get from a computer power supply output to a circuit.

I also didn't have 2N2222 or 2N5904 transistors, I used 2N3904s, which seem to work fine.

-73-


Category: Electronics

This still feels like yesterday's repair, even though it was tonight when I did all this.

Since I had the final module out from yesterday, I hooked power to it to test.  I first tried the driver, and it didn't trip the circuit breaker.  Then I tried the high power amp and it tripped the circuit breaker immediately.  Fearing the worst, I embarked on the long process of removing the finals (which was not fun because of how they were stuffed in there.

Finals

Finals in their copper case. Getting the heatsink off wasn't too difficult, but getting the circuit board out of the copper was a pain.

Finals

After a lot of work with a heatgun and soldering iron and wick and a bulb, I got this out.

Final PA Transistors

These are the finals after being removed.

So after removing these, I put them on an octopus tester, and tested them.  The results are interesting.  It also says that one or both of them is likely bad.  These things aren't cheap, but with how much of a pain it is to remove them, the smart thing would be to replace both, since one went, the other is likely not far behind.

2013-08-18 22.55.28

Note: the upper-left and middle-right are nowhere near the same:

Oscilloscope Image

Upper Left

Oscilloscope Image

Middle right

Next up: replacing the transistors and powering the unit back on!

-73-


Category: Equipment
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