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Re: QCX-mini LCD Back-light - spurious voltage

 

Hi Sam. I think your idea of faulty Q100 could be correct. To make sure first, though, please measure the voltage?on the gate of Q100 while switching the backlight mode on and off in the menu. You need to turn it on, then back out of that menu item for it to activate. Similarly, when you turn it off, it doesn't go off until you cvak out of the menu item. Anyhow, when it is on, you should see some voltage like 5 volts on the gate of Q100, and with it off, that should go to zero.?

R65 is in the circuit that sets the display contrast so should be in there. I don't find an R50 in my units. Maybe I'm missing it. R48 definitely needs to be in there to pass current to the anode of the backlight LED.?

If that resistor is in place?and gate voltage is swinging normally, go ahead?and replace Q100.

Good luck ..... Ron

On Sun, Jan 29, 2023 at 6:35 AM Samantha Collins <samcollins910@...> wrote:
QCX MINI working fine but have no back-light.?
This didn't concern me at first power up as I knew it was configurable in the menu.? However having dome some digging I'm a little concerned.?
LCD pin 15 is showing 10v and it should be 5v
?Pin 16 that should be ground is showing 12v...? overall rx current draw is 101mA, this is what drew me to poke around with the DVM as its a little on the high side.?

Could this be a failed Q100??

I'm going to desolder pins 15 and 16 while I investigate further, not overly concerned about not having a back-light. Hopefully that will reduce the overall current draw.?

Any advise on what to look at would be greatly appreciated?

Sam

Just to cover the bases I have gone over the boards with a magnifying glass and there are no solder blobs, bridges, crooked components, loose or unsolderd pins or legs
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