Re: QCX-20 No power output at all

James Daldry W4JED
 

Hi, Jim

Check for zero ohms from the center pin of the antenna jack to C29. Check for infinite ohms from the antenna jack center to ground. Both conditions must be present for the RF to get out of the radio. If there is no continuity, there probably is a lead on L1, L2, or L3 that was not sufficiently cleaned of enamel. If there is a short to ground, use a magnifying glass on both sides of the board, looking for solder strings on the bottom and wire clippings on the top.

The 5.2 watt reading at the FET drains has meaning. It means the entire transmitter chain is working. So you just have to find the road block. You're very close to having a working transmitter.

Jim Daldry W4JED

On 1/22/19 5:19 PM, secondchancesailor wrote:
My QCX-20 has no power output.  When I key down, I can hear the signal in my TS-440, and if I place a frequency counter near the PA it will read the output frequency.   But there is nothing at the RF output.

Initially, when transmitting on 7020, the output was actually on 7048.   I recently built a QCX-40 with no issues, and had to make just a very small adjustment in the reference frequency to put it on frequency.  But in this 20 meter kit, I had to set the reference frequency to 27,057,900 to get the output to match the displayed frequency - a larger error than I expected.        

So far, I have carefully checked the circuit board for any solder bridges or breaks using a magnifier hood, but found none.    Using the built-in RF Power meter to check the drains of Q1, Q2, and Q3 I read 5.2 watts, but I have read in other messages that that doesn't necessarily mean anything.   I have checked the continuity of L1, L2, and L3, and removed a couple of turns from each as has been suggested, with no change.    I can read 5.2 watts on one side of C29, but nothing on the side that goes to L3.   I pulled C29 and it measured ok, but I replaced it anyway, and still no output.     I have to admit that troubleshooting isn't really my strong suit, and I don't have much in the way of equipment.   Any help to point me in the right direction would be greatly appreciated!

Jim (w8ykg)   

Join QRPLabs@groups.io to automatically receive all group messages.