I built QMX ver. 3 and the rig worked fine. Yesterday I was doing some measurements on the PA and the rig shut down. After unplugging the oscilloscope, it wouldn't turn on. I found that the 5 V and 3.3 V power supplies were missing. At 12 V power supply on PCB plug-in #2, transistor Q102 did not close. Q101 on drain 12 V, on gate 0.75 V and the transistor is also open. The CPU is without power, so "LIN_REG_EN" should also be disconnected, and there should be about 6V at the gate of Q101. The resistance between the gate and GND is 50K. I pulled out PCB plug-in #2 and did another resistance measurement. The resistance between gate and GND was 100K. On the main PCB the resistance between "LIN_REG_EN" and GND is out of ohm meter range. I connected the 7 V power supply to PCB plug-in #2, voltage appeared on IC101 but it started to heat up, so I did not finish the measurement and disconnected the PCB. Can anyone advise me how to detect the fault?
Jirka OK1DDQ
