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Hi folks!

I just completed assembly of my QMX and am eager to validate and tune it.

upon applying power and usb-c I do not see a flash drive.

QMX V3 device & Debian (12) Linux
- lsusb shows no new devices
- dmesg shows no new kernel events
- tried holding the left rotary control down for various iterations of time 1,5,10,20 seconds etc.
- poured over all the boards multiple times with magnification and good lighting.
- all diode polarities validated (installed right way round.
- I tested all the continuity test points described in the build manual
- tried different cables, different PC, different OS validated my cables using smartphone and usb drive
- I looked for the possible short on the mosfets on the power supply daughter cards no short between the tab any other traces.

Not sure of my next step in troubleshooting.

Also I noted that when testing voltages on the SMPS 5v supply
- I see the input voltage at whatever I set it 8-12volts
- I hear the audio amp pop in headphones when pressing left encoder
- the current draw is only .05 MA if the left encoder is pressed down. when I release it goes back to zero.
- I never see other voltages apart from the input voltage on either power supply board.

Could my issue be the SMPS board(s)?
What should my next troubleshooting steps be?

Best regards & 73's
Gordon Young - WA8Q

Gorden, in this document from QRP Labs Wiki you find a description of the switch on process, about the levels of some signals and also a link to a sketch to find these signals.

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I think you came only to the first step of the description. Maybe one of the relevant connections to/from the SMPS boards is not ok. Checking the mentioned signals and levels you should find the failure. Please be aware a failure may also exist between the pin headers of the main board and the SMPS.

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73 Ludwig

On Mon, Jul 15, 2024 at 02:41 PM, @Ludwig_DH8WN wrote:

Ludwig,
Thank you for the guidance & fast response!
I'm going to give this a shot tonight.

Best regards!
~G
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so far I get
- correct BAT_LEVEL value
- PWR_ON pulled down when left encoder depressed

no 3.3 volts present at ?LIN_REG_EN
when depressing the left rotary encoder the voltage at LIN_REG_EN goes to .75 3/4 of a volt but never 3.3 regardless of BATT input voltage.

I wonder if that means I have an issue with my PCB #2?

Cheers!
~Gordon

On Tue, Jul 16, 2024 at 01:46 AM, Gordon Young wrote:

so far I get
- correct BAT_LEVEL value
- PWR_ON pulled down when left encoder depressed

no 3.3 volts present at ?LIN_REG_EN
when depressing the left rotary encoder the voltage at LIN_REG_EN goes to .75 3/4 of a volt but never 3.3 regardless of BATT input voltage.

Gordon,

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please follow the description in the Wiki document. Regarding the second point voltage at "+12V" should come up after PWR_ON goes down. Without this voltage nothing will work.

Did you solder both sides of the female pin header to the SMPS subboards?

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73, Ludwig

Hi Ludwig,

Again thank you kindly for the guidance!

regarding the labeling on the diagram here:
/g/QRPLabs/files/QMX%20PSU%20pinout/QMX%20Pinout%20Drawing.pdf

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With 12v applied, when I press and hold the left rotary encoder

Further: nothing seems to "latch", what I mean is: the moment? I release the left encoder button the 12 volts on PBC1&2 and LEN_REG_EN .75v voltages disappear.

Regards!
~Gordon

On Thu, Jul 18, 2024 at 02:28 AM, Gordon Young wrote:

+12V on PCB#2 comes up to 12v

Gordon, a step forward.

Now we have to find the problem related to LIN_REG_EN. We should use schematics page 1 to discuss (don't worry, it's simple in this region).

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LIN_REG_EN comes from the controller. In case the controller doesn't run and it isn't broken the resistance from the controller pin to GND should be very high (some 100 kohm or more). When both SMPS boards are removed you could check this using your DMM. If you find a much lower value (only some kohm or less) something is wrong on the main board. In this case check resistance VDD to GND. It should be around 10 kohm or so. If only a few ohms or less an element connected to VDD is broken, maybe the controller.

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On SMPS board #2 R101 and R115 are building a voltage divider between "+12V" and GND. Check the removed SMPS #2 board for resistance from "12V" to LIN_REG_EN and for LIN_REG_EN to GND. Both values should be around 100 kohm. If much lower, the SMPS board is not ok (wrong resistors, broken Q101, a tin whisker around).

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If all is ok until now, check the SMPS board #2 off line. Connect a voltage of around 6 V ... 12 V "+12V" (don't forget the GND ;-). The voltage at LIN_REG_EN should be around half of your test voltage. If much lower, the SMPS board is not ok (wrong resistors, broken Q101, a tin whisker around).

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73, Ludwig

The outcome:

LIN_REG_EN to ground =? 11.3 MΩ (megaOhms)

VDD to ground 1Ω ohm

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SMPS #2 board

~6v in? =? ~3 vout

Based on the outcome I suspect:
- something in the path VDD is defective
or
- the Micro-Controller it's self is defective

Thoughts?
Thank you kindly for helping me troubleshoot this!
Best regards
~G

On Fri, Jul 19, 2024 at 05:26 AM, Gordon Young wrote:

- something in the path VDD is defective
or
- the Micro-Controller it's self is defective

Gordon, maybe it's the same. A defective Controller would affect VDD and LIN_REG_EN.

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I wonder why LIN_REG_EN is pulled down with this value. I think the resistance is non linear. Up to 0.75V the value is high and starting from 0.75V very low like for a Si diode.

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I don't know if an other broken element connected to VDD would affect the controller in this way or the controller have to produce this effect by itself.

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Sorry but no experience here for further debugging in this state. Maybe someone else could share his own experience. I wish you success.

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73, Ludwig

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Hi Ludwig,
Thank you for all the support!? No worries at all.
I'm going to further study the schematic & decide if I need to replace any components in the path of VDD or attempt to replace the STM32.
These radios are (in relative terms) inexpensive to purchase. I'm sure I'll snag another kit and do another build. Who knows maybe I can resurrect this one still!