On Sat, Mar 29, 2025 at 12:10 PM, Nico Smith wrote:
On IC101 it goes to 3.2 then 1.7 volts when. I press the button.
It draws 0.7 amps when pressing the button.?
0.7A is way too much, about 3x normal, confirming something is shorting.
Also, on JP106, there is no power.
I don't quite understand your description of the voltage measurement.? Are you looking at the output pin of the IC101 regulator (the one closest to the diodes and coil)?? And it is 0V before pressing the button, then briefly goes to 3.2V, and then to 1.7V when you press the button?? Or is it 3.2V before pressing the button, then goes to 1.7V when pressing?? Or are you looking at the input pin (closest to card edge)?
It is useful to know the voltages on both the input and output pins of IC101 both before and while pressing the button, and after releasing the button.?
Also please the voltages on +V, Vcc, and Vdd before and while pressing the button.? These are found in that order, in JP105, adjacent to D108 and C107 - they are the inner set of the two rows of 3 small holes.? (Vcc and Vdd are also in JP106, where you say you saw no power, so they may show nothing again).? If there is truly 0V (or very close to 0V) on Vdd while pressing the button, you likely have a shorted D109 (i.e. it did its job in protecting from overvoltage), and hopefully no damage to the processor or other 3.3V parts.
And one more set of measurements: with QMX+ unplugged, measure the resistance between +12V and gnd, Vcc and gnd, and Vdd and gnd.? Each of these should be a few k-ohms.? Then measure the resistance directly between each of the three voltages.? These should all be very high, in the mega-ohm range.
These measurements will help diagnose where the problem is, and if there are other problems besides the likely D109.?
?
By the way, looking at your setup - I would buy an inexpensive 3A drock boost/buck converter, set it to 12.0V output, and wire it into the cable coming from your power supply to your QMX+.? That way you can leave the power supply set at the best voltage for your Kenwood, and still always have the correct power set for your QMX+, ensuring power mistakes don't get made.? And depending on which model you buy, it will have a current limit you can set while debugging.? (The current limit may only work if you don't ground your QMX directly to the Kenwood, due to the design of the drok, but that's easily avoided during debug).
Stan KC7XE
