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On Mon, Jul 24, 2023 at 10:58 PM, <Ugglekatten@...> wrote:

My newly built QMX has a strange behaviour...
When supply voltage is 9V current consumption on receive is 110mA on tranmit 1.27A
Output power is fine on all bands.
I can hear signals on all bands
But when i raise supply voltage to 10.5V the current consumtion goes to 220mA, at 11V it goes to 300mAn (always in receive)

Hi Gunnar.? You say that the QMX works fine with good receive and output power when operating with 9V.? Why are you trying to run a higher voltage supply?
?
--
Peter Lee
G3SPL

Peter,

Gunnar should be able to receive at 12v without drawing excessive current. Had he wired for 12v operation, that would be mandatory. I believe he is correct in his assessment that something is amiss.

JZ KJ4A?

On Tue, Jul 25, 2023, 6:37 AM G3SPL <leepd60@...> wrote:

On Mon, Jul 24, 2023 at 10:58 PM, <Ugglekatten@...> wrote:

My newly built QMX has a strange behaviour...
When supply voltage is 9V current consumption on receive is 110mA on tranmit 1.27A
Output power is fine on all bands.
I can hear signals on all bands
But when i raise supply voltage to 10.5V the current consumtion goes to 220mA, at 11V it goes to 300mAn (always in receive)

Hi Gunnar.? You say that the QMX works fine with good receive and output power when operating with 9V.? Why are you trying to run a higher voltage supply?
?
--
Peter Lee
G3SPL

Gunnar,

It is as if the feedback loop that controls the bias buck converter is not working.

Check at both sides of R505 to make sure the ADC is getting a converter output sense signal. Check at the gate of Q501 to make sure a controlling PWM signal is present.

JZ KJ4A?

On Tue, Jul 25, 2023, 7:05 AM John Zbrozek <jdzbrozek@...> wrote:

Peter,

Gunnar should be able to receive at 12v without drawing excessive current. Had he wired for 12v operation, that would be mandatory. I believe he is correct in his assessment that something is amiss.

JZ KJ4A?

On Tue, Jul 25, 2023, 6:37 AM G3SPL <leepd60@...> wrote:

On Mon, Jul 24, 2023 at 10:58 PM, <Ugglekatten@...> wrote:

My newly built QMX has a strange behaviour...
When supply voltage is 9V current consumption on receive is 110mA on tranmit 1.27A
Output power is fine on all bands.
I can hear signals on all bands
But when i raise supply voltage to 10.5V the current consumtion goes to 220mA, at 11V it goes to 300mAn (always in receive)

Hi Gunnar.? You say that the QMX works fine with good receive and output power when operating with 9V.? Why are you trying to run a higher voltage supply?
?
--
Peter Lee
G3SPL

Gunnar, one more thing...

With power off check the resistance from Q502 gate to drain and gate to source. If a short to gate has developed both Q502 and Q501 will exhibit elevated temperatures.

JZ

On Tue, Jul 25, 2023, 7:35 AM John Zbrozek <jdzbrozek@...> wrote:

Gunnar,

It is as if the feedback loop that controls the bias buck converter is not working.

Check at both sides of R505 to make sure the ADC is getting a converter output sense signal. Check at the gate of Q501 to make sure a controlling PWM signal is present.

JZ KJ4A?

On Tue, Jul 25, 2023, 7:05 AM John Zbrozek <jdzbrozek@...> wrote:

Peter,

Gunnar should be able to receive at 12v without drawing excessive current. Had he wired for 12v operation, that would be mandatory. I believe he is correct in his assessment that something is amiss.

JZ KJ4A?

On Tue, Jul 25, 2023, 6:37 AM G3SPL <leepd60@...> wrote:

On Mon, Jul 24, 2023 at 10:58 PM, <Ugglekatten@...> wrote:

My newly built QMX has a strange behaviour...
When supply voltage is 9V current consumption on receive is 110mA on tranmit 1.27A
Output power is fine on all bands.
I can hear signals on all bands
But when i raise supply voltage to 10.5V the current consumtion goes to 220mA, at 11V it goes to 300mAn (always in receive)

Hi Gunnar.? You say that the QMX works fine with good receive and output power when operating with 9V.? Why are you trying to run a higher voltage supply?
?
--
Peter Lee
G3SPL

Thank you all for your answers, I will try to answer all your questions in the order received:

Peter G3SPL, well I noted that the minimum power consumption occurred at 9.2V.
If everything was OK it would get lower at higher voltage, but not.
This is an indication that something is not right

John Z and Alan, you came to the same conclusion as I did

All measurements are taken with a supply voltage of 9.0V

John Z:
both sides of R505 show 0.749V DC, no AC signal superimposed
PWM signal on the gate of Q501 is only present during transmit, amplitude 3.3V, goes to 0V between pulses
The strange thing is that in receive it does not rest at 0, it rests at 1V. Looks like the PWM output is changed to an input at receive

Q502: resistance gate to source 700kOhm, gate to drain 740 kOhm
Q501: resistance gate to source 10/7.3? kOhm, gate to drain 12/28 kOhm The first value with the plus tip ov the DVM connected to the gate, the second with the minus tip

My own conclusion: the signal on the gate of Q501 should be at 0V in receive... maybe i should try with a 10kOhm pulldown resistor in parallell with R502??

br SM5EIE / Gunnar

Gunnar,

Your observation of 1 volt at the PWM input is strongly suggestive of a gate to drain short in Q501. The resulting current flow into the microcontroller pin could overwhelm its ability to hold a down level.

Check that Q501 for unusual gate to drain resistance. With power off you should see numbers in the vicinity of 100K ohms. Much less would indicate a gate oxide failure in Q501.

JZ

On Tue, Jul 25, 2023, 10:20 AM <Ugglekatten@...> wrote:

Thank you all for your answers, I will try to answer all your questions in the order received:

Peter G3SPL, well I noted that the minimum power consumption occurred at 9.2V.
If everything was OK it would get lower at higher voltage, but not.
This is an indication that something is not right

John Z and Alan, you came to the same conclusion as I did

All measurements are taken with a supply voltage of 9.0V

John Z:
both sides of R505 show 0.749V DC, no AC signal superimposed
PWM signal on the gate of Q501 is only present during transmit, amplitude 3.3V, goes to 0V between pulses
The strange thing is that in receive it does not rest at 0, it rests at 1V. Looks like the PWM output is changed to an input at receive

Q502: resistance gate to source 700kOhm, gate to drain 740 kOhm
Q501: resistance gate to source 10/7.3? kOhm, gate to drain 12/28 kOhm The first value with the plus tip ov the DVM connected to the gate, the second with the minus tip

My own conclusion: the signal on the gate of Q501 should be at 0V in receive... maybe i should try with a 10kOhm pulldown resistor in parallell with R502??

br SM5EIE / Gunnar

John,
since the microcontroller can get the PWM voltage down to 0 during transmit, it looks more as if the microcontroller changes the port to an input port for some reason.
I attach an image from the oscilloscope showing the beginning of a transmission

John,
I accept your analysis, thank you!
What finally convinced me was that if I put a pull-down resistor of 2.2kOhm in parallell to R502 the drain voltage of Q501 change is only about 10mV up.
It is steady at 7.38V when the source voltage of Q502 is 8.97V.
It should be the same, so the conclusion is that Q501 is leaking!
I will replace it.
Thank you very much for your help

73 de SM5EIE / Gunnar

Yezz !!
I replaced Q501, it was not the easiest task, but I got it done.
Now everything is fine !!
Input current at 9V is 125mA, at 12V it is 100mA with backlight on

Put another feather in your hat John !
(I dont know is this swedish saying is translatable to english, but I think you grasp the meaning...)

73 de SM5EIE / Gunnar