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Dear group

Took me a long time but finally I have finished a build of a Qmx plus rev 2 (my 3rd kit) and when powering it up nothing happens.?
so I start debug the power supply with the following tests:?

initially power with 12v (500ma) and nothing no display no nothing power consumption arround 9ma when the button is pressed, I release the button and back to 0ma.

so I have check if the 3v out where in ic101 with the button pressed and nothing there. Than the input and strangely nothing there even with the buton pressed. Next step I apply directly 7v on its input and I get 3v on the out put. Seams working consumption also increases to some hundreds of ma meaning the STM32 can be working.?
then I was checking q101 and q102 and I get when I press the button arround 5v on q101 out and 11.5 on q102 out with 12v input again.?
the problem is that on the ic101 I don’t see the 11.5 v. Seams that the line is broken.

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did some one experienced something like this??
what should I do next??
73

Azgael

On Sun, Mar 30, 2025 at 01:02 PM, Azgael wrote:

arround 5v on q101 out and 11.5 on q102 out

What do you mean by out? Which voltage at "+12V"? Which voltage at LIN_REG_EN when pressing the encoder?

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Please read QMX QMX_plus Startup to see how start up is going in detail and which voltage at which point in which state of start up.

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73 Ludwig

Hi Ludwig?

I have been following that sequence despite talking about Qmx and not Qmx+ with embedded sources for 3 and 5v.?
The voltage out on the mosfet I meant is the drain voltage on both of them. Meaning the q101 opens and feeds the gate of q102 with the 5v from its drain. Than q102 opens and at it’s drain I have arround 12v.?
For me the lin-reg-en voltage is not so relevant since I have passed that point.?
following the voltage path I should have the 12v on the vin of IC101 but nothing arrives there, all this when the button is pressed. So it never start to generate the 3v the stm never starts.?
I will have to feed the Ic101 manually directly on vi with 12v and see if the system starts and keeps operating, but not done yet.

Hi Azgael, it seems that you're saying the drain of Q102 is not connected to the input of IC101? If that's the case it might indicate a manufacturing error in the PCB. On rev3, Q102 and IC101 are on the different sides, but there's a hole nearby through which you can solder a short jumper wire to connect the pins. I guess you can do the same on rev2.

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73 N6HAN

Hi Zhenxing?

Thanks, I will do that! But if it works, God knows how many other tracks or vias are open or broken.?
will be able to do it only tomorrow but will keep You posted.?
BR

Azgael

On Sun, Mar 30, 2025 at 05:41 PM, Azgael wrote:

following the voltage path I should have the 12v on the vin of IC101 but nothing arrives there

Hi Azgael, yes, drain of Q102 and VI of IC101 must show the same voltage.

But 5 V at drain of Q101 is strange. If the controller doesn't work the gate of Q101 is pulled to 50 % of "+12V", so here around 6 V. In this state drain of Q101 should have something close to 0 V and not 5V. I would check the reason for this.

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73 Ludwig

On Sun, Mar 30, 2025 at 08:03 PM, Azgael wrote:

God knows how many other tracks or vias are open or broken.?

I would be surprised if this connection is broken.

Finally success following the power pad did help. Surprisingly enough there seams to be a broken via or track connecting source of q102 to ic101 to input. ?Now I am a bit concerned with other issues with this PCB.?

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Now the fix simple wire connection?

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BOOM IT WORKS

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seams not to have any other issue with the 5 and 3v, but as I said no idea about any other via issue!!

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Thank You very much for the feedback Ludwig and Zhenxing was a good tip! 73

Azgael

The last screen shot!

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73

Azgael

On Mon, Mar 31, 2025 at 05:10 AM, Azgael wrote:

there seams to be a broken via or track connecting source of q102 to ic101 to input.

Azgael,

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Your fix is not quite what you think.

You did indeed connect the Source of Q102 o the input of IC101.?

But the schematic connects the Drain of Q102 to IC101 input.

What you did is bypass the Q102 switch, enabling your QMX to power up.?

This bypassed the fault - which is either a fault in Q102 or Q101 or the signal at LIN_REG_EN, as previously discussed.

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So there likely is no broken trace on your board, just a misunderstanding of source/drain connection on the schematic.? And you have nothing to worry about additional board defects (these boards are tested, so as Ludwig noted, we would be very surprised if any trace was bad).

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Your QMX+ will work fine this way, but will have the linear regulator on all the time, which consumes an extra few 10s of milliamps, so if you are operating on batteries they will not last quite as long.? The diode D103 allows both supplies to be on with no damage.

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Stan KC7XE

Dear Stan

Now makes more sense this all thing.

Basically I do have continuity between the drain of Q102 and In of IC101, NO ISSUE on the Via as you and Ludwig mentioned.

Further debugging, I measure the LIN_REG_EN and I get 2.6v when the button is pressed meaning at gate of q101 i have now 2.6v not the previous 5v (something else seams to be wrong now).

Can some one guide me on debugging LIN_REG_EN?

Thanks

73

Azgael

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On Tue, Apr 1, 2025 at 12:00 PM, Azgael wrote:

I measure the LIN_REG_EN and I get 2.6v when the button is pressed meaning at gate of q101 i have now 2.6v

Azgael, if not alredy done please remove the black wire.

At least from 2 V up at gate of Q101 the voltage at drain should be near 0 V. You see 2.6 V at the gate, enough.

Please check voltage at drain of Q101 (or at gate of Q102). If voltage at gate of Q102 is lower than voltage at source of Q102, in worst case 2 V or more, voltage at drain of Q102 should be close to voltage at source of Q102. Which voltages do you see?

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And voltage at drain of Q110 should also be near 0 V.

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73 Ludwig

On Sun, Mar 30, 2025 at 10:55 PM, @Ludwig_DH8WN wrote:

If the controller doesn't work the gate of Q101 is pulled to 50 % of "+12V",

To be right, there was an error in my previous post. If the controller doesn't work the gate of Q101 is pulled to (or near) the voltage at "+12V", not only 50 %.

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73 Ludwig

Thanks again Ludwig,

The Voltage at the Drain Q101 (Gate Q102) is 9.7v, the voltage at Gate Q101 is 2.6v, source Q101 is 0V and the voltage at Source Q102 is nearly 12v and at Drain Q102 is 0V (With 2.3v difference Source to Gate I was excepting to have approximately 12V).

73 Azgael

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On Tue, Apr 1, 2025 at 04:05 PM, Azgael wrote:

The Voltage at the Drain Q101 (Gate Q102) is 9.7v, the voltage at Gate Q101 is 2.6v,

Hello Azgael, 9.7 V is wrong for this gate voltage. It looks like Q101 is broken.

the voltage at Source Q102 is nearly 12v and at Drain Q102 is 0V (With 2.3v difference Source to Gate I was excepting to have approximately 12V).

Yes, it's also wrong. It looks like Q102 is also not ok.

If you remove Q101 use the chance to measure voltage at LIN_REG_EN. The voltage should be near "+12V" for your Rev. 2 QMX+. (For some Rev. of QMX the voltage is only 50% of "+12V". For some Rev. a voltage devider is used and for some not. Check schematics for your Rev. to find the right value.)

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73 Ludwig

Hi Ludwig

I have ordered the correct Mosfets should arrive tomorrow, I will measure the LIN_REG_EN and then solder the mosfets, just to confirm the LIN_REG_EN should be 12V when the button is pressed in hardware version QMX+ if QMX (No +) with different revisions might have only 6V, correct?

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73 Azgael

Azgael, please check schematics for QMX+ Rev. 2 / 3 page 1.

Gate of Q101 together with LIN_REG_EN is connected via R101 to "+12V". With pressed vol-encoder and not running controller LIN_REG_EN is pulled to around the voltage at "+12V". After the controller gets VDD via IC101, starts to run and VDD is proper generated via Q109 the controller will pull LIN_REG_EN low to around 0 V.

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Checking schematics Rev. 4 for QMX you will find nearly the same things but additional R115 from LIN_REG_EN to GND, forming a voltage divider 0.5:1. This pulls LIN_REG_EN for the start only to 50% of "+12V".

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But if you would see also only 50% of "+12V" at LIN_REG_EN of your QMX+ maybe R115 is hidden somewhere in the "deep parts" of QMX+ schematics.

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73 Ludwig

Dear Ludwig

Here follows the next chapters!

I have removed Q102 and Q101 and tested the LIN_REG_EN at the gate of Q101 I got +/-0.6V when pwr button is pressed. So my LIN_REG_EN is being puled down or shorted some where, for sanity I follow the signal pad and I removed the Q110 just in case. I measure again same +/-0.6V.

So now the only connection to the LIN_REG_EN is the STM32, same +/-0.6v on the LIN_REG_EN, seams that the Microcontroler without power is puling the signal down leading it not to start at all.

For sanity I replaced the pull-up resistor R101 and R102 (just in case) same status.?

In my guess I pin pointed this the a problem with the STM32.

SO.... now the hard part... disconnect the SPM32 Pin 88 from the LIN_REG_EN! Done... and confirmed the LIN_REG_EN now measure 12v as VIN. ?

The problem seams to be with the STM32 from the beginning, (So no via issue!!!!Sorry for that one) probably no issue with Q101 and Q102.?

Any way I might be wrong!

Question is what to do next I would like to have the QMX + fully working, some how the STM32 got damaged or came like that.

And thank You so much for the support!

73 Azgael

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On Fri, Apr 4, 2025 at 06:33 PM, Azgael wrote:

SO.... now the hard part... disconnect the SPM32 Pin 88 from the LIN_REG_EN! Done.

Good job but bad outcome.

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To replace the STM32 you need one prepared by QRP Labs. If you are located in W you may contact Jeff Moore or else QRP Labs direct.

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73 Ludwig

One question, reading older posts in this thread the QMX+ was running. But when and why died the controller now?

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73 Ludwig