Several people reported that the adjustment of the IQ-Balance with R27 didn't do what was expected.

At first I had the same experience, but after turning the other two trimmers halfway, everything adjusted as described.

Since I think the trimmers are delivered all turned CCW, a suggestion is to first turn R14 and R24 some 5 turns CW, and then start tuning R27.

IQ Balance, Lo and Hi Phase null not adjusting

This was the second most common issue reported. It occurs across all the models for various reasons.

Users who report getting a good BPF adjustment but the phase adjustments can't be made because the volume can't be set to a level above “1” or the volume cannot be set lower than level “13”, usually have an issue with the volume pot being poorly soldered on the high side or wiper (low volume level) or the ground side (high volume level).

On QCX Classic models I found this volume pot issue was usually due to poor solder connection to ground.

On QCX+ models the issue on two of them was a damaged potentiometer. Bending the leads caused a disconnect of the bradded connection between the lead and the carbon trace on the pot. This was fixed by squeezing the brad with a thin pair of needle nose pliers.

On QCX Mini models the most common issue was improper soldering of the 2X4 header on top of the control board. The pins on this header do not protrude all the way through the control board. They need a lot of heat and good solder flow down into the plated-through holes with good adhesion to the pin inside the hole. Other issues on the control board can be caused by this and may be mentioned later in this article. One Mini had a bad volume pot and it had to be replaced. It was noisy and it is not repairable.

On one unit, this issue was caused by a leaky C12 which was making no phase change possible at IC6A.
An intermittent C1 on an early Classic model was causing issues with this as well as wth BPF peaking.
IC4 was bad on a few units with this issue. This was usually caused by putting 112 volts on the 5 volt bus and caused other issues as well with failures of most or all of the 5 volt ICs.
Open circuit trace between R17, C10 and Pin 5 of IC6. This was a classic model and was repaired with a short 3-way jumper.
On the Rev 1 version of the QCX Mini, several different models had this issue and other issues due to bad op amps. This was a known problem and corrected with new parts and board tests with the release of Rev 2 of the Mini.
C5 was installed on a 20 meter Mini. The 20 meter and higher units do not use this part. Bandpass filter could not be aligned and test signals were also so weak that the phase and balance adjustments weren't possible either.
IC10 had the wrong bias voltage. This was caused by a cut lead on one of the bias resistors (R39 & 40).

Hi Mark

Thanks for your suggestion.
I have tried centring all 3 pots, first by screwing all the way in then out by 13 turns. I also centred them using using my multimeter to find the centre.
I have tried adjusting the hi setting first as some have suggested. I have tried starting with each one a 1/4 out then 3/4 out while trying to get any sort of adjustment.
Nothing seems to make any difference on the balance, low or high.

Paul

When using the TCXO module option, change menu item 8.5 Ref frq to 25,000,000. It
is critical to this before any further alignment. Enter the menu system as described
below, and turn to menu 8.5, edit it to 25,000,000.

...you would expect to see a combined resistance of around 7.142k (this is the 25k of the trimmer mid-point in parallel with the 10k fixed resistor in each case).