Sunday, February 23, 2014

Ugly Weekender VFO Board Trials and Travails..

It's FINALLY up on on the bench again and under scrutiny. As I surmised, my careless slapping of components into holes and soldering them together led to a non-working VFO board. Here is a blow-by-blow of what I know.

The difficulty in assembling this kit from collected parts and the FAR boards is that the original transmitter article was done in typical ARRL QST slap-dash fashion: no corresponding part numbers for the labelled components and no means to relate the silkscreen markings on FAR's boards to the original schematics.

But, no one promised you a rose garden, eh?

Firstly, here is the schematic I have been working from:

Here is the whole board on the test bed. The quality is not the greatest but it gives you the view from 20,000 feet.

Here is the lower left hand corner of the FAR board where the keying and spot switches are located. I noted from the original transmitter article, it was keyed from the VFO so I chose to close the circuit there. Those are the yellow and black lines heading off board.

Here is the first problem area I encountered. D1 is the diode next to the 1 megohm R17. Careful inspection will reveal that the little bastage was wired in backwards. See the diode cathode band on the North side of the PCB while the actual component's cathode band is facing South. If you look closely, you can see the silk screened diode band peekign up fromt he gold tolerance band on the 1 megohm resistor.

I reversed the diode and got nothing radically changed, so I trucked on. Basically, there are two points of curiosity in debugging this board: What actually does one short to test the board (key versus "spot" switch?) I voted for the key jack. This is sort of outlined below in the picture.

And one final mystery remains. How are the holes below populated? They are marked as C46 and C14. The latter is easy enough to dispose of as the circuit indicates it to be a 0.01 uFd cap. However I am all at sea when it comes to C46. It is not called out in the schematic so far as I can see and yet it is strapped across to D2 to ground. I suspect it is a 0.01 uFd as well but will check with Alan and the QRP Tech Yahoo crew for their opinions and insights.

Here are the voltages I measured:



Stephen Roberts said...

Did u ever find out what C46 was all about?
Steve, W1SFR

The War Planner said...

..never did. Dropped this project like fourth period French.