My first time QCX build - fail.


Jim - K9DD
 

I finished my QCX 40 this morning and no go. I guess these 72 year old eyes failed me. It powers on, display is good but when I plug headphones in I get a loud tone and nothing else. According the display, it appears to tune the band and I can get all the menus. I hooked an antenna to it and briefly hit the key and could hear a signal on another receiver.

I had to leave but am going to keep checking for solder bridges, cold joints, etc tonight unless someone has any suggestions.

Thanks for any help.
Jim - K9DD


N3MNT
 

You will get a loud tone on headphones if you are in in alignment mode


Braden Glett
 

Jim, as others have noted, the most likely culprit is a bad connection on one of the toroid leads. Check connections there first!
GL
Brady kd8zm


Jim - K9DD
 

It is in any mode except when I key the transmitter and is not affected by the volume control.


Jim - K9DD
 

I don't understand enough to see why those connections would cause the tone when in any mode except transmit but I'll certainly check them.

Thanks


Gary Freeman
 

Ted - I had a similar experience.  Be sure you are using a stereo plug in the key jack.  The QCX requires one.  If you put in a mono plug it just keys the transmitter, and the tone you hear may be the side tone. 

After my build I heard a tone, so I took my time to carefully do the alignment steps.  That ruined my finals because they were on transmit for so long,  To make sure, when you're doing alignment just unplug the key from the jack and use the little onboard key.

I had to replace several transistors.

That may not be your problem, but it is one to avoid.

72 and good luck
Gary W0ITT

 


Gary Freeman
 

Oops, sorry.  I meant Jim, not Ted  :-)

72 de Gary W0ITT


Jim - K9DD
 

I've made progress but it still isn't working right. I rewired T1 and reinstalled it. That fixed the loud tone but I caused more problems. I lifted a trace off the board from pin 4 of T1. It appears to me to go to the source of Q5 so I hooked it directly to it. It now seems to work but I can't hear anything but noise and clicking when on an antenna. Also, now when I key the transmitter I can barely hear it in another receiver where before it was a strong signal. I'm close to giving up. I no longer have test equipment except a DMM.


Curt wb8yyy
 

Jim

I strongly suggest not transmitting until the receiver is working. Unplug the key or paddle.

On my build I missed on solder connection in the audio section. I found the issue by turning on the alignment source, yes free test equipment already built in. I poked around and found my issue. Also as mentioned its easy to not get the enamel off the toroid connections.

You have enough test equipment,  please slow down and I think you may solve it.

Keep in touch

Curt


Jim - K9DD
 

Thanks for your confidence. I'm going to put it aside for awhile and think about it. 

I may order another kit and try again.


Charles W. Powell
 

Take heart, Jim.  I had a problem with my first QCX.  I did just that - set it aside - and then built another.  After that I traced down the problem in the first build without any sophisticated test gear.  I only had a screwdriver that made a dandy noise injector, and a multimeter that showed me where the fault was.

72,

Charles - NK8O

On Sep 3, 2018, at 5:08 PM, Jim - K9DD <jdawson@...> wrote:

Thanks for your confidence. I'm going to put it aside for awhile and think about it. 

I may order another kit and try again.


Jim - K9DD
 

Thanks Charles. I'm ordering another tonight.

Jim - K9DD


Braden Glett
 

Jim: My first QCX was also a fail. I had another one and decided to do some things differently to remove possible errors. The main thing was, I sorted all of the components, testing each one to ensure they were the correct values. That way, when it came time to install all of the (for example) 10k resistors, I just reached into the 10k resistor tray and installed them - not much potential for error, this way. Doing it this way, the QCX fired up first thing.
When you're building this, it's a long process and easy to get fatigued, which makes us error-prone. Pre-sorting removes a lot of the potential for mistakes. I recommend this approach highly.
Brady kd8zm  


Curt wb8yyy
 

Most of the complexity here is in the receive chain, so something amiss may take out one of the two parallel chains, or in some cases both of them.  Note we need to achieve 100% success in mounting parts, or nearly so, to achieve a good unit.  The built-in test source is very useful in debugging the receiver. 

I would carefully check polarity of each part having polarity, electrolytic caps and diodes especially. 

I had great difficulty reading the tiny parts placement labels on the board.  So I didn't !  I set up a laptop on the bench next to the kit, and the nice color coding in the manual helped greatly.  There is this small chance than one could make the same mistake in two different kits so be careful with parts ID and placement. 

An audio source makes for easier signal tracing.  Then you can work your way back to the front of the receive chain and see where signal is lost.  Note you can use a wire to jump over the LPF to verify whether its the problem. 

don't ask my batting average in getting kits to work upon first applying power.  I remember 3 errors in building my K2.  The last error I could not find, but I solved it by reflowing solder of every connection in the area where I had the issue - that solved it - undoubtedly a faulty solder connection. 

Best wishes in a successful build. 

Curt


Jim - K9DD
 

Success! I found my problem. Besides rewinding and remounting the T1, I found a cold solder joint on C1. Those two things fixed it and I made my first contact! 

Thanks for all the help,
Jim - K9DD


 

Excellent,  Jim.  T-1 is a pain to wind - it took me two tries to get it right

Enjoy the rig — you will be amazed how far 5 Watts can travel. My best DX is Poland — about 4300 Miles.
--
73, Bernie, VE3FWF


Jim - K9DD
 

Now I found another problem. I thought the alignment went ok but now the bandpass filter only shows a strength of 4 instead of 7-9 like the trouble shooting guide says.I no longer hear any signals. Don't know whereto start.


 

Review the solder joints again with a magnifier or eye loop and touch up any suspect solder joints. 
--
73, Bernie, VE3FWF