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Author Topic: Swan 700cx receive coil adjustment L801  (Read 509 times)
AC0FA
Member

Posts: 298




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« on: January 18, 2007, 09:06:26 AM »

Good Morning

I was am able to get the rig to recieve.
While doing a receive alignment as described in the book. I put my rubber gloves on and adjusted L801 the first IF coil.

Something really bizare started happening. As long as I was holding on to the end of the allen wrench,

(I have since bought a plastic adjusting tool)

with it inserted into L801 the forst IF coil. The rig would beautifully. If I let go of the end of the wrench the receieve went away.

I moved on to the first if amp V8 pin 5 If I hold on to the capacitor C801 I have recieve when I let go it goes away.

I am not sure exactly where the problem lies.
For example L801 Coil or C801 capacitor or if the problem is somthing completly different like cut off voltage?

What can I do t fix?

Erik AC0FA

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KA5N
Member

Posts: 4380




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« Reply #1 on: January 18, 2007, 04:33:18 PM »

Well hi Erik
C801 couples the IF signal OUT of the 1st IF.  If it was bad it might keep the TX from working, but not the receive (unless shorted).  The problem must be in the first IF amp tube circuit.  L801 may be open. Such coils will often have a bad solder joint at the terminals or a broken wire.  Be very careful with the tuned coils, replacing one will be nigh impossible as there is no Swan factory.  Check R 802 and R 803.  Check the plate and screen grid voltages. (Heck the tube might be bad or have a bad solder joint at one pin.  
What is happening is that the receiver mixer is working so the IF signal is present and when you touch this or that you are acting as an antenna and injecting the signal into the 2nd IF amp.  You might try removing the 1st IF tube and temporarily connecting a small value capacitor (100 pf) from the control grid to the plate thus by passing the stage. A great increase in signal would confirm that the stage is NOT working.  Be sure that the rig is unplugged when you connect the cap.
Also when you are repairing a receiver you usually shuld start at the audio output and work backwards toward the input.
Another way to test the IF stages is to couple in an IF signal from a signal generator.  Going backwards, when you hit a stage that is not ampliflying, there's your culprit.
Good Luck Allen
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