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QMX Question for Troubleshooting

 

Is it OK to apply power to a QMX when the LCD and Controls Boards are removed?

?

If so,? is it then OK to turn on the VDD supply by manually grounding the PWR_ON line at the input connector of PCB #1?

?

NOTE:? This QMX is a 9V, user built, 60-15m unit that comes up with no VDD at power turn on.? If VDD did come up,

I assume the QMX?would be in the initial power up mode for loading firmware so only the linear IC101 VDD would be expected.

?

Don WB0LQW
 

Donald Adams via groups.io <djadams42@...> wrote:

Is it OK to apply power to a QMX when the LCD and Controls Boards are
removed?
Yes.

If so,? is it then OK to turn on the VDD supply by manually grounding
the PWR_ON line at the input connector of PCB #1?
Yes.

NOTE: This QMX is a 9V, user built, 60-15m unit that comes up with no VDD at power turn on.? If VDD did come up,

I assume the QMX?would be in the initial power up mode for loading firmware so only the linear IC101 VDD would be expected.
Is +12V (after power switch) present? Well, in your case it will be +9V,
but the line is still labeled +12V...
 

I built my 9V 60-15 last weekend.? To troubleshoot it I would leave the display board off and start it up with the control board.? After I established Terminal App connection I would pop the control board off, only if I needed to access underneath it.? Not always good to pull things off under power but mostly this board provides inputs to the main board so probably reasonably safe to do.
?
Brien - KE7WB
 

May not be a problem in this case, but I'd recommend at least an alligator clip jumper to keep the grounds connected while unplugging the front panel.? Generally, if the ground pins disconnect before the VCC pins do, power might find a return path through the signal pins and smoke an IO cell somewhere.
Jerry, KE7ER
?
?
On Wed, Jan 8, 2025 at 02:38 PM, Brien - KE7WB wrote:

I built my 9V 60-15 last weekend.? To troubleshoot it I would leave the display board off and start it up with the control board.? After I established Terminal App connection I would pop the control board off, only if I needed to access underneath it.? Not always good to pull things off under power but mostly this board provides inputs to the main board so probably reasonably safe to do.
?
Brien - KE7WB
 

Thanks, Adam.
No, "+12V" (needs a new label) is not present, at least as far as can be determined with measurements on the main PCB.
A connection problem in the PCB #1 connector could explain this.? That's why I want to get to the board with the power on
and the power supply activated via PWR_ON.?
?
The "+12V" is in the lower row of pins on the PCB #1 connector, inaccessible with the board plugged in, but I can get to the
drains of Q103 and Q103 by probing the top side of the board.? That's where I'm headed.
?
Don WB0LQW
 

Brien,
I don't have the courage to unplug the hot boards.? Besides, if there is no VDD I don't think I could connect PuTTY.
I don't think? USB would be working.
?
Don WB0LQW
 

Don,
?
Not sure why VDD would not be there with 9V applied to the input plug.? It works fine with only the control board plugged in and push on the left encoder to turn it on.? Then the USB port works fine.? If I had to guess, this is built into the the design to be able to test the main board independently during manufacturing.? It worked for me.? By all means, if your worried about hot unplugging the control board, don't.
?
Brien
 

Don,
?
I re-read your previous post and realized that you were working a problem where you did not have Vdd.? In that case I understand why the USB interface might not work.? Apologies for the confusion.
?
Brien - KE7WB

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