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QMX+ high pitch noise on power. Now dead.

 

I was just building a microphone for the qmx and then I plugged it into my power supply to test it. I on purpose to turn the voltage down from 13.8 and then turn it on. It worked fine but I needed to turn it off and back on again for it to connect to my computer. I turned it off and then when I tried to turn it back on it was a high-pitched noise for about half a second in the screen backlight turned on and then it turned off and now shows no signs of Life except power draw when I press the button.

8mb.video-Tkg-0QTQ6fpv.mp4
8mb.video-Tkg-0QTQ6fpv.mp4

 

When you turned it off and back on, did you do it with the switch on your power supply, or with the QMX front button?
?
Your symptoms are that you now have an internal power fault, which prevents the QMX+ from powering on.
One possibility:? If the input voltage from your power supply ever exceeded 14V, for more than a second or two, even with the QMX+ turned off, or if there was a high voltage transient from the power supply, it may have fused the input protection TVS diode (D110).? 13.8V on continuously for a period of time possibly could also damage that diode, which starts conducting somewhere between 13V and 14V.? There are of course other possibilities, only measurements will tell.
?
It will be best to turn down your voltage to about 7V and set a 250mA current limit while diagnosing this, if possible, to avoid any new faults.
Stan KC7XE
 

I turned it off with the QMX power switch. Earlier today it was exposed to more voltage for a short period of time but it was still working fine after that. I'm not very good at reading schematics but what measurements should I do?


On Thu, Mar 27, 2025, 11:44?PM Stan Dye via <standye=[email protected]> wrote:
When you turned it off and back on, did you do it with the switch on your power supply, or with the QMX front button?
?
Your symptoms are that you now have an internal power fault, which prevents the QMX+ from powering on.
One possibility:? If the input voltage from your power supply ever exceeded 14V, for more than a second or two, even with the QMX+ turned off, or if there was a high voltage transient from the power supply, it may have fused the input protection TVS diode (D110).? 13.8V on continuously for a period of time possibly could also damage that diode, which starts conducting somewhere between 13V and 14V.? There are of course other possibilities, only measurements will tell.
?
It will be best to turn down your voltage to about 7V and set a 250mA current limit while diagnosing this, if possible, to avoid any new faults.
Stan KC7XE
 

Where is D110 on the qmx board? I can try to check its state.


On Fri, Mar 28, 2025, 6:17?AM Nico Smith via <nicosmith873=[email protected]> wrote:

I turned it off with the QMX power switch. Earlier today it was exposed to more voltage for a short period of time but it was still working fine after that. I'm not very good at reading schematics but what measurements should I do?


On Thu, Mar 27, 2025, 11:44?PM Stan Dye via <standye=[email protected]> wrote:
When you turned it off and back on, did you do it with the switch on your power supply, or with the QMX front button?
?
Your symptoms are that you now have an internal power fault, which prevents the QMX+ from powering on.
One possibility:? If the input voltage from your power supply ever exceeded 14V, for more than a second or two, even with the QMX+ turned off, or if there was a high voltage transient from the power supply, it may have fused the input protection TVS diode (D110).? 13.8V on continuously for a period of time possibly could also damage that diode, which starts conducting somewhere between 13V and 14V.? There are of course other possibilities, only measurements will tell.
?
It will be best to turn down your voltage to about 7V and set a 250mA current limit while diagnosing this, if possible, to avoid any new faults.
Stan KC7XE
 

I just checked the diode and it seems to be fine with a 0.6v drop.


On Fri, Mar 28, 2025, 6:27?AM Nico Smith via <nicosmith873=[email protected]> wrote:

Where is D110 on the qmx board? I can try to check its state.


On Fri, Mar 28, 2025, 6:17?AM Nico Smith via <nicosmith873=[email protected]> wrote:

I turned it off with the QMX power switch. Earlier today it was exposed to more voltage for a short period of time but it was still working fine after that. I'm not very good at reading schematics but what measurements should I do?


On Thu, Mar 27, 2025, 11:44?PM Stan Dye via <standye=[email protected]> wrote:
When you turned it off and back on, did you do it with the switch on your power supply, or with the QMX front button?
?
Your symptoms are that you now have an internal power fault, which prevents the QMX+ from powering on.
One possibility:? If the input voltage from your power supply ever exceeded 14V, for more than a second or two, even with the QMX+ turned off, or if there was a high voltage transient from the power supply, it may have fused the input protection TVS diode (D110).? 13.8V on continuously for a period of time possibly could also damage that diode, which starts conducting somewhere between 13V and 14V.? There are of course other possibilities, only measurements will tell.
?
It will be best to turn down your voltage to about 7V and set a 250mA current limit while diagnosing this, if possible, to avoid any new faults.
Stan KC7XE
 

For that TVS diode (right alongside the power connector), the forward 0.6V drop is not the critical thing - it is the reverse breakdown, and I'm not sure if the 'diode test' function of a multimeter can test that.
?
The first measurement I would do is to plug in the 12V power, and then measure the voltage (Vin) on the QMX board, perhaps on the center pin of the power connector.? If the voltage is down well below 12V, then that TVS diode has likely failed.? If it still is at 12V, and no power supply current draw, then the failure is likely elsewhere.
?
Which rev of QMX+ board do you have?? The rev 1 with the SMPS power supplies on the little cards?? If so, you can test them separately via the procedure in the wiki.
?
Stan KC7XE
 

I have rev 2. When I plug in the power it still shows as 12 on the board. It only draws power when I press the power button.


On Fri, Mar 28, 2025, 4:13?PM Stan Dye via <standye=[email protected]> wrote:
For that TVS diode (right alongside the power connector), the forward 0.6V drop is not the critical thing - it is the reverse breakdown, and I'm not sure if the 'diode test' function of a multimeter can test that.
?
The first measurement I would do is to plug in the 12V power, and then measure the voltage (Vin) on the QMX board, perhaps on the center pin of the power connector.? If the voltage is down well below 12V, then that TVS diode has likely failed.? If it still is at 12V, and no power supply current draw, then the failure is likely elsewhere.
?
Which rev of QMX+ board do you have?? The rev 1 with the SMPS power supplies on the little cards?? If so, you can test them separately via the procedure in the wiki.
?
Stan KC7XE
 

Next I would measure the voltage at each of the three terminals of IC101, the 3.3V regulator, when you press the power-on button.? ?But don't press the button for more than a second or so, since it could cause more damage, since it does not appear that you have a way to limit the current.?
?
Also, do you have a way to measure the input current, with more resolution than that ammeter on your power supply? It looks like it is going up to almost 1A, but I'm sure it is not accurate at that range.? If there is not an internal power short, it should only read about 200mA while pressing the button.?
?
Your symptoms indicate that you probably have a failure in your 3.3V power supply (or a device that is connected to) such that the processor can't power-on and set the power to stay on.
?
Stan KC7XE?
 

On IC101 it goes to 3.2 then 1.7 volts when. I press the button.

It draws 0.7 amps when pressing the button.


On Fri, Mar 28, 2025, 11:31?PM Stan Dye via <standye=[email protected]> wrote:
Next I would measure the voltage at each of the three terminals of IC101, the 3.3V regulator, when you press the power-on button.? ?But don't press the button for more than a second or so, since it could cause more damage, since it does not appear that you have a way to limit the current.?
?
Also, do you have a way to measure the input current, with more resolution than that ammeter on your power supply? It looks like it is going up to almost 1A, but I'm sure it is not accurate at that range.? If there is not an internal power short, it should only read about 200mA while pressing the button.?
?
Your symptoms indicate that you probably have a failure in your 3.3V power supply (or a device that is connected to) such that the processor can't power-on and set the power to stay on.
?
Stan KC7XE?
 

Also, on JP106, there is no power.


On Sat, Mar 29, 2025, 3:10?PM Nico Smith via <nicosmith873=[email protected]> wrote:

On IC101 it goes to 3.2 then 1.7 volts when. I press the button.

It draws 0.7 amps when pressing the button.


On Fri, Mar 28, 2025, 11:31?PM Stan Dye via <standye=[email protected]> wrote:
Next I would measure the voltage at each of the three terminals of IC101, the 3.3V regulator, when you press the power-on button.? ?But don't press the button for more than a second or so, since it could cause more damage, since it does not appear that you have a way to limit the current.?
?
Also, do you have a way to measure the input current, with more resolution than that ammeter on your power supply? It looks like it is going up to almost 1A, but I'm sure it is not accurate at that range.? If there is not an internal power short, it should only read about 200mA while pressing the button.?
?
Your symptoms indicate that you probably have a failure in your 3.3V power supply (or a device that is connected to) such that the processor can't power-on and set the power to stay on.
?
Stan KC7XE?
 

On Sat, Mar 29, 2025 at 12:10 PM, Nico Smith wrote:

On IC101 it goes to 3.2 then 1.7 volts when. I press the button.

It draws 0.7 amps when pressing the button.?

0.7A is way too much, about 3x normal, confirming something is shorting.

Also, on JP106, there is no power.

I don't quite understand your description of the voltage measurement.? Are you looking at the output pin of the IC101 regulator (the one closest to the diodes and coil)?? And it is 0V before pressing the button, then briefly goes to 3.2V, and then to 1.7V when you press the button?? Or is it 3.2V before pressing the button, then goes to 1.7V when pressing?? Or are you looking at the input pin (closest to card edge)?
It is useful to know the voltages on both the input and output pins of IC101 both before and while pressing the button, and after releasing the button.?
Also please the voltages on +V, Vcc, and Vdd before and while pressing the button.? These are found in that order, in JP105, adjacent to D108 and C107 - they are the inner set of the two rows of 3 small holes.? (Vcc and Vdd are also in JP106, where you say you saw no power, so they may show nothing again).? If there is truly 0V (or very close to 0V) on Vdd while pressing the button, you likely have a shorted D109 (i.e. it did its job in protecting from overvoltage), and hopefully no damage to the processor or other 3.3V parts.
And one more set of measurements: with QMX+ unplugged, measure the resistance between +12V and gnd, Vcc and gnd, and Vdd and gnd.? Each of these should be a few k-ohms.? Then measure the resistance directly between each of the three voltages.? These should all be very high, in the mega-ohm range.
These measurements will help diagnose where the problem is, and if there are other problems besides the likely D109.?
?
By the way, looking at your setup - I would buy an inexpensive 3A drock boost/buck converter, set it to 12.0V output, and wire it into the cable coming from your power supply to your QMX+.? That way you can leave the power supply set at the best voltage for your Kenwood, and still always have the correct power set for your QMX+, ensuring power mistakes don't get made.? And depending on which model you buy, it will have a current limit you can set while debugging.? (The current limit may only work if you don't ground your QMX directly to the Kenwood, due to the design of the drok, but that's easily avoided during debug).
Stan KC7XE
 

The output of the IC101 is 0V before pressing the button, then briefly goes to 3.2V, and then to 1.7V when I press it. When you press the button input starts at 12 then goes down to 10 then 8.

+V, Vcc, and Vdd are all zero without pushing the button.
When pushing the button. +V = 12V. Vcc = 160 mV. Vdd = 1.6 V

Resistance to ground:
+V = 25 K Ohms
Vcc = 3.68 K Ohms
Vdd = 202.4 Ohms

Vcc to Vdd = 1.4 K Ohms
Vdd to +V = 18 K Ohms
Vcc to?+V = 18 K Ohms

Is there a way I can check D109?

Thanks for all the help!

On Sat, Mar 29, 2025 at 4:25?PM Stan Dye via <standye=[email protected]> wrote:
On Sat, Mar 29, 2025 at 12:10 PM, Nico Smith wrote:

On IC101 it goes to 3.2 then 1.7 volts when. I press the button.

It draws 0.7 amps when pressing the button.?

0.7A is way too much, about 3x normal, confirming something is shorting.

Also, on JP106, there is no power.

I don't quite understand your description of the voltage measurement.? Are you looking at the output pin of the IC101 regulator (the one closest to the diodes and coil)?? And it is 0V before pressing the button, then briefly goes to 3.2V, and then to 1.7V when you press the button?? Or is it 3.2V before pressing the button, then goes to 1.7V when pressing?? Or are you looking at the input pin (closest to card edge)?
It is useful to know the voltages on both the input and output pins of IC101 both before and while pressing the button, and after releasing the button.?
Also please the voltages on +V, Vcc, and Vdd before and while pressing the button.? These are found in that order, in JP105, adjacent to D108 and C107 - they are the inner set of the two rows of 3 small holes.? (Vcc and Vdd are also in JP106, where you say you saw no power, so they may show nothing again).? If there is truly 0V (or very close to 0V) on Vdd while pressing the button, you likely have a shorted D109 (i.e. it did its job in protecting from overvoltage), and hopefully no damage to the processor or other 3.3V parts.
And one more set of measurements: with QMX+ unplugged, measure the resistance between +12V and gnd, Vcc and gnd, and Vdd and gnd.? Each of these should be a few k-ohms.? Then measure the resistance directly between each of the three voltages.? These should all be very high, in the mega-ohm range.
These measurements will help diagnose where the problem is, and if there are other problems besides the likely D109.?
?
By the way, looking at your setup - I would buy an inexpensive 3A drock boost/buck converter, set it to 12.0V output, and wire it into the cable coming from your power supply to your QMX+.? That way you can leave the power supply set at the best voltage for your Kenwood, and still always have the correct power set for your QMX+, ensuring power mistakes don't get made.? And depending on which model you buy, it will have a current limit you can set while debugging.? (The current limit may only work if you don't ground your QMX directly to the Kenwood, due to the design of the drok, but that's easily avoided during debug).
Stan KC7XE
 

It is a bit hard to test a zener, especially a low-voltage one in circuit.
I just measured mine with the diode test function of my multimeter, and it measures 0.31V in one direction, and 0.44 volts in the other.
I don't know what that really means, but if yours is broken, you will likely see something different.
?
The way I have normally tested D109 is to remove it, then power on and see if the rig wakes up normally.? If it does, I know that D109 was bad and replace it.? I do NOT recommend you do this, because you have no current limit on your supply, and D109 will not be there to protect your processor and other 3.3V devices if there is still a problem.? Instead, I would replace it before trying to power on again.? Then if there is still a problem, D109 will conduct the over-voltage to ground and not harm your other ICs.
?
D109? is very small and nestled between two other devices, so be sure you have the practical skill (practice helps a lot) to replace it before trying; otherwise send it to someone else to fix.? I can look, I may have an extra one I can send you if you don't have one but do have the skill to replace it.
?
Stan KC7XE
 

My dad has a nicer power supply that does have current limiting. I can test on that tomorrow. What is the maximum amperage I should allow?

I think I could replace the diode but if I can't my dad definitely can. He was trying to help me but he just doesn't understand the circuit that much.


On Sat, Mar 29, 2025, 9:51?PM Stan Dye via <standye=[email protected]> wrote:
It is a bit hard to test a zener, especially a low-voltage one in circuit.
I just measured mine with the diode test function of my multimeter, and it measures 0.31V in one direction, and 0.44 volts in the other.
I don't know what that really means, but if yours is broken, you will likely see something different.
?
The way I have normally tested D109 is to remove it, then power on and see if the rig wakes up normally.? If it does, I know that D109 was bad and replace it.? I do NOT recommend you do this, because you have no current limit on your supply, and D109 will not be there to protect your processor and other 3.3V devices if there is still a problem.? Instead, I would replace it before trying to power on again.? Then if there is still a problem, D109 will conduct the over-voltage to ground and not harm your other ICs.
?
D109? is very small and nestled between two other devices, so be sure you have the practical skill (practice helps a lot) to replace it before trying; otherwise send it to someone else to fix.? I can look, I may have an extra one I can send you if you don't have one but do have the skill to replace it.
?
Stan KC7XE
 

Set the current limit to 250mA and the voltage to 7V until it starts up and works correctly in receive mode?
 

That was it!!! Do you have any spare diodes to replace it with? I don't have any and I don't want to run it without.


On Sat, Mar 29, 2025, 10:22?PM Stan Dye via <standye=[email protected]> wrote:
Set the current limit to 250mA and the voltage to 7V until it starts up and works correctly in receive mode?

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