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QCX-20 No power output at all

secondchancesailor
 

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)   

Bill Cromwell
 

Hi Jim,

Is your new radio drawing enough current to make that 5 watts?

If that cap is not open (apparently not, look for a short to ground beyond the cap. Is your antenna connector actually connected to the circuit board? That happened to me one time. <hanging head in shame>

73,

Bill KU8H

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)
--
bark less - wag more

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)   

secondchancesailor
 

Well, here is another one for the sheepish ham department:   I spent more hours than I would like to admit, trying to figure out why I had no power output.   It turns out it was just a stupid mistake.  When I built the 40 meter version of this kit, I mounted all the controls on the circuit board.  When I decided to mount that radio in an ammo case, it was quite a task to remove everything.  So on the 20 meter kit I mounted all controls off the board to begin with, which included running a short piece of RG316 to an SO239.   I then covered the center conductor with some tape.    In moving the radio around, the center conductor had broken loose from the SO239 -  but I didn't know it because of the tape.   I removed the coax for now,  and mounted the BNC connector to the circuit board - and I now have 1 1/2 watts output (12 volt supply) according to an MFJ QRP wattmeter (whose accuracy is questionable).   I may see if I can improve the output a little more, but am happy to have a working radio!   Thanks to KU8H, W4JED, and KQ4TQ for the replies and suggestions!

73,
Jim W8YKG