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Hi,

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I wanted to measure the power consumption, so I connected the QMX to my lab supply with an ampere meter.

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The connection was not reilable.
First the QMX started normally. When I moved it, there must have been a very short disconnection to power.
It showed black boxes? on the screen and made a hissing sound.

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When I press ON now, it draws 0.7 A on 12 V. The linear power regulator 78M33C heats up quickly. No light, no display.

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Any chance, that I can repair the QMX?

Which components can be broken?

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Thanks

Vy 73 de Peter DL4PJ

Peter,

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it could be just that D108 Z-diode mentioned here:

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73, Andreas

Thanks for the info!

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PCB#2 (3.3V) is definitely kaputt, I did these tests:

My VDD: 0.5V

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On Sun, Aug 11, 2024 at 03:02 PM, Peter Jacobi wrote:

Question: where is D109?

Peter, use the assembly manual section "PCB diagrams". Ok it's a lttle bit hard to read D109. Afaik it's the diode at the edge of the PCB and close to D103. Zoom in in the PDF and you will find something like "D109".

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73 Ludwig

There have been some upgrades to the power supply boards to make them more robust over time (higher wattage zener, higher voltage tantalum capacitor). So depending which Rev QMX pcb yours was built from, and when purchased, the best course of action may be to purchase a new power supply board set from QRP-Labs.?

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My first Rev 1 QMX had a similar fate.?

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73
de Roy - KI0ER
Littleton, Colorado USA

Peter,

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Before you invest in new power boards, I suggest verifying that Vdd is not shorted to ground on the main board.? That indicates MPU failure that can only be fixed with a new kit.

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73

Evan

AC9TU

Thanks!

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I'll have to purchase a new board.

I removed D109.

The function was better, but VDD? has been off a bit and sometimes higher as 4V. so I decided to try it with 12 V...

... with PWM 3_3 still on "High" which means 12V in my case! Bad Idea!

... Smoke.

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Conclusion:
The board had a malfunction. D109 did its function and HOPEFULLY saved the rest of the QMX.

On Sun, Aug 11, 2024 at 05:03 PM, Peter Jacobi wrote:

The function was better, but VDD? has been off a bit and sometimes higher as 4V.

Peter, in which situation, using the liear regulator or testing the SMPS off line? If testing the SMPS off line you have NO regulation. You test only the ON / OFF behaviour (and a little bit more.)

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73 Ludwig

Thanks Ludwig,

I see.

I tested everything in an isolated setup.

I understood too late that the voltage will be unregulated and the tantalum capacitor burned. Impressive fireworks!

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I will check the Mainboard with a PBC2 from a friend and order new boards.

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73 Peter DL4PJ?

Peter,

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but first check resistance VDD to GND and VCC to GND for only the main board!

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73 Ludwig

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Thanks Ludwig,
I followed your advice:

85kOhm to 100 kOhm?

=>shouldn't destroy the PCB2.

Do you think, it's safe to connect a LAB 3.3V supply to the mainboard?
Will? the boot routine detect this fake supply and refuse to boot or will I be able to do further diagnostics?

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Peter

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On Sun, Aug 11, 2024 at 07:47 PM, Peter Jacobi wrote:

Do you think, it's safe to connect a LAB 3.3V supply to the mainboard?

Peter,

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someone reported in this forum a while ago he was doing so. Afaik QRP Labs is doing also this to check each main board including the USB connection.

I think with installed firmware you may come to a working controller and USB connection. Via terminal you may reach only Diagnostics. But I never checked this.

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73 Ludwig

It doesn't look so bad.

I connected VDD to my 3.3V Lab supply, 12V to my powerbank and USB.
The Serial console coes up.

Not as usual into the menu, but directly into a diagnostic screen, where you can test the buttons.

All button presses are recognized.

Let's hope, that a new PCB2 module will do the rest.

vy 73, Peter DL4PJ

Check all component for having enough space. Coils, holder, everything.

Sometimes you need to bend some thing like the metal what hold the lcd in place on its own pcb.

I had some issue while i plugged the earphone or paddel. The qmx turned off, but luckily no damage.

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I'm running my QMX on a couple of linear regulators.? I managed to fit a couple of TO220 linears onto some veroboard which fits inside the case and plugs into the PSU connectors on the main board.

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Chris, G5CTH

Hi,

My QMX is back to life!!!
Only the 3.3V supply board had to be changed.

I didn't discover any other faults yet.

The rest of the QMX seems to be really robust against peaks.

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Vy 73, Peter DL4PJ