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QMX+ debug

 

Dear all

I have completed my build of QMX+.

On applying power current consumption is zero.

When I press and hold the power encoder the current draw increases to 9ma at 12V but returns to 0 as soon as I stop pressing (long press over 5 seconds).

I dont know what to try now - no device appears on PC when current draw is 9ma.

Can you offer any suggestions on how to begin to debug?

Mark
G0MGX
 

I've started to investigate and find the following:

Vin measures as expected on the plug-in PCB #1
When I press the power on encoder button the PWR_ON line is grounding as expected
With the PWR_ON grounded the +12V line measures as expected?
I can find the +12V feeding Q102 on the Plug-in PCB #2?
There is +12V on both the source and gate of Q108 but no voltage on the drain and therefore no voltage on D106.

Anyone cleverer than me able to shed any light?

My assumption is that I need PCB#1 to generate VCC so I can load firmware - at the moment nothing at all is happeneing as I only have a +12V rail.

Mark G0MGX
 

On Fri, Jun 14, 2024 at 08:36 AM, Mark wrote:
There is +12V on both the source and gate of Q108 but no voltage on the drain and therefore no voltage on D106.
Mark,

no problem in this state.

The switch on process is explained here in detail (for QMX but it's the same for QMX+). For the next steps the "left part" of PCB#2 (see schematics) is important.

73, Ludwig
 

Hi? Ludwig

Very helpful thank you.

I understand the circuit?so much?better now :-)

I have?+12V being supplied to Q102 on plug-in PCB #2 but not passing to IC101.

If I remove plug in-pcb #2 and apply 12V to the board alone, then it works as expected and the regulator is generating the expected voltage, but not when in the main PCB connector.

I am finding that the LIN_REG_EN line is being pulled low - I measure around 1 ohm between this pin and ground on the main PCB when the plug-in PCB #2 is removed.

As far as I can tell, this is a direct line to the MCU PD7 pin 88 - I can't?see anywhere else where it is on the PCB to look for issues?

Mark
G0MGX

On Fri, 14 Jun 2024 at 11:11, DH8WN via <DH8WN=[email protected]> wrote:
On Fri, Jun 14, 2024 at 08:36 AM, Mark wrote:
There is +12V on both the source and gate of Q108 but no voltage on the drain and therefore no voltage on D106.
Mark,

no problem in this state.

The switch on process is explained here in detail (for QMX but it's the same for QMX+). For the next steps the "left part" of PCB#2 (see schematics) is important.

73, Ludwig

 

On Fri, Jun 14, 2024 at 03:56 PM, Mark wrote:
As far as I can tell, this is a direct line to the MCU PD7 pin 88 - I can't?see anywhere else where it is on the PCB to look for issues?
?
Mark, whats with the pin header JP104. Maybe a nearly invisible short there?

If the 1 ohm would be caused by the controller, that would be bad. So please check two more points:
- resistance of VDD to GND and
- resistance of PWR_HOLD (PCB #1) to GND.
All this with subboards removed from the mainboard.

73 Ludwig
 

hi Ludwig

It seems I am confusing myself?and maybe need to stop looking for a while.

My 1R reading is on the main board between VDD and Ground (not LIN_REG_EN) - so I have a short circuit somewhere - this is with all sub-boards removed.

I also find D103 missing - I think it has acted like a fuse and gone pop - even though max current draw has been 9mA.

Mark

On Fri, 14 Jun 2024 at 15:37, DH8WN via <DH8WN=[email protected]> wrote:
On Fri, Jun 14, 2024 at 03:56 PM, Mark wrote:
As far as I can tell, this is a direct line to the MCU PD7 pin 88 - I can't?see anywhere else where it is on the PCB to look for issues?
?
Mark, whats with the pin header JP104. Maybe a nearly invisible short there?

If the 1 ohm would be caused by the controller, that would be bad. So please check two more points:
- resistance of VDD to GND and
- resistance of PWR_HOLD (PCB #1) to GND.
All this with subboards removed from the mainboard.

73 Ludwig

 

After a great deal of searching I think I have a conclusion - albeit something I can't rectify.
?
Fault was 0.8R between VDD and 0V. Never tested until construction was complete but have to assume this was not the case on leaving the factory.
?
Every component between VDD and ground checked and double checked - no joy.
?
As a last resort, and after much heat from the rework station (on 420deg and max airflow) and much chipquik flux the STM32 MCU has been lifted off the board and the short has gone - VDD to 0V now measures ~9k.
?
I have no hope of getting a replacement fitted so the board is now scrap.
?
I'd love to know what people think went wrong, feeling somewhat disappointed ?.
?
Mark
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