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No audio at BPF adjustment #alignment #antenna

Gary Bernard
 

Greetings to all. I'm a really old ham, tubes and transformers etc. and the microprocessor stuff I don't understand.
I finished a QCX 20. The display works and I can access all menu items. However I do not have side tone when adjusting the BPF and C1 seems to have no effect. There is a low level hum  and the gain control has no effect..
When I go in to menu 9 it shows zero volts and.01 watt.
A series of T's will show on the display.
I have checked all solder joints, have continuity at the toroids and T1. Same with the gain control.
I guess I'm at a loss as to what should be the next step.Any help would be much appreciated.
Regards, Gary W0CKI

Stephen VE6SVJ
 

This sounds similar to my recent trouble... try swapping out the audio gain pot. Worked for me... except I busted the second one and now need to replace it again.

The 0 Volt and 0.01W... to get a Volt reading in menu 9, you need to jumper the measurement and DVM pins. You also need to jumper them to use the battery level display.

73,

Stephen.
VE6SVJ

fred.g3srf@...
 

There seems to be a lot of posts relating to the audio gain pots breaking. I have used pots of various types for may years and have never had a mechanical problem. After many years service, some may go scratchy but that is the carbon track just wearing out.
Is the current failure rate due to a cheap version being supplied or due to the constructor mis-handling them.
If similar ones are to be supplied in the future QSX kits, perhaps it may be better to replace them at the outset.

Hans Summers
 

Hi Fred

From all the reports I have heard, and samples we take of stock, and the QCX kits we build here - I believe the failure rate of the audio gain pots to be very low - I think somewhat under 1%. 

Regarding QSX, QSX is internally a Software Defined Radio. During the early design stage I eliminated the audio gain potentiometer. This was not for reasons of reliability of the potentiometer. It was because both performance AND cost could be optimized without it. 

Performance-wise it was possible in the Digital Signal Processing to arrange a true logarithmic volume control (which is expensive if done with an analog pot). Furthermore, since the QSX has a stereo audio output, it permits adjustment of the relative volume between Left and Right channels. A dual-gang analog volume control would have cost more and had more tabs to break. The separate channels are useful for reception modes such as binaural reception, and the dual receiver option. The dual receiver option allows you to listen to two different frequencies, one in each ear; with a separation of several kHz (somewhere in the range 12-24kHz, not sure precisely yet). A 24-bit DAC is used, so that there is plenty of dynamic range available. 

Surprisingly, this approach also lowered the part-count and reduced the cost. 

Therefore there are in QSX, two rotary encoders; one to the left of the display and one to the right. Ordinarily left = volume, right = frequency tuning; but of course either one can serve multiple purposes and can be reconfigured by you as you wish. 

73 Hans G0UPL

On Tue, Feb 26, 2019 at 12:23 PM <fred.g3srf@...> wrote:
There seems to be a lot of posts relating to the audio gain pots breaking. I have used pots of various types for may years and have never had a mechanical problem. After many years service, some may go scratchy but that is the carbon track just wearing out.
Is the current failure rate due to a cheap version being supplied or due to the constructor mis-handling them.
If similar ones are to be supplied in the future QSX kits, perhaps it may be better to replace them at the outset.