No sidetone on QCX #qcx #sidetone


 

There is no sidetone but only a slight hum  and key click  when keying the QCX.  This is a new fault which may have been caused by accidentally keying the rig without an antenna for about 2 seconds.  
 

I searched the archives but nothing came up regarding this problem.

The QCX sounds fine on the air and the RX is OK as well.

I changed Q6 as I thought that might be the problem.  And while I was at it, I updated the firmware to 1.07a. There is sidetone coming from the micro on R59  according to the scope.


Perhaps 🤔 the RX/TX transistor  Q5  is the problem?    I hate to change parts without understanding  the root cause.

 

Next  step suggestions most welcome.


73, Bernie, VE3FWF
(most typos in this message have been generated by highly sophisticated auto-correction software)


Russ AB6MU
 

Hi Bernie,

Have you watched the Youtube video that Hans posted on debugging the QCX? If not, you may find it helpful.

Debugging QCX issues, using cheap pocket scope, DVM or built-in DVM. With 40m QSO at the end

Russ


howard winwood G4GPF
 




I changed Q6 as I thought that might be the problem.  And while I was at it, I updated the firmware to 1.07a. There is sidetone coming from the micro on R59  according to the scope.


if you see the sidetone at R59, you then need to trace it through IC8b (pin 7), IC8a (pin 1),IC9b (pin7), IC9a (pin 1) via volume pot and Q7 to IC10b (pin7), IC10a (pin 1) to headphones.
The pins quoted are the output pins on each op amp


 

Howard:

I do get sidetone when the QCX is in Keyer Setup mode.  The sidetone is not heard once the QCX is actually transmitting CW.
--
73, Bernie, VE3FWF
(most typos in this message have been generated by highly sophisticated auto-correction software)


 

Russ

Thanks for the suggestion. 


I will follow the signal flow through the receiver section when the rig is transmitting based on the video that Hans made. Somehow, RF is getting into the RX portion of the QCX.

--
73, Bernie, VE3FWF
(most typos in this message have been generated by highly sophisticated auto-correction software)


 

Problem solved.  Q5, the TX/RX switch was bad.  Probably leaking too much RF into the RX  chain during transmit.
NOTE: Failure was probably caused by transmitting with no antenna for about 2 seconds
--
73, Bernie, VE3FWF
(most typos in this message have been generated by highly sophisticated auto-correction software)