Hi everyone!
Yesterday I managed to get my QMX up and running, what a beautiful device.
I made a few *mistakes and encountered a few hiccups along the way, so I thought I would share them here.
I encountered 2 main issues: Magic smoke, and a problem where the radio enters the ¡°shut down!¡± state immediately after booting.
Problem 1: Magic smoke on the 5V SMPS
Once assembled (and inspected according to the manual), I connected a *non-limited 10V power supply to the rig, without enclosure. I could boot the device and upload the firmware, success!
Frying the power supply PCB:
I went ahead and put the thing into the aluminium case. Next, I *connected a 12.5V (measured) battery and the device wouldn¡¯t boot anymore. Opening the case revealed the magic smoke. L101 was hot and I knew that at least the 5V SMPS board was gone.
I don¡¯t know what caused this failure. Possible causes:
- The use of a 12.5V battery for the first boot after installing the enclosure
- A short caused by inserting the assembly into the aluminium case. Perhaps a component to the case, or a component of the SMPS board to the main board. It is a very tight package!
- Others
Checking if the MCU is OK:
I removed all boards (LCD, control, 2x PS) and connected 3.3V to Vdd. I could still connect to the processor via Putty ¨C phew!
I reinstalled the 3.3V power supply board and hooked up 9V to the +12V pin. In this configuration I could also connect to the processor and I could check that Vcc was 3.3V (by using the Diagnostics tool via Putty). Nice!
I suspected that the 5V portion of Plug-in PCB #1 was toast (Q108, D106, D108, C107 etc.) and ordered a new one.
Problem 2: QMX enters ¡°shut down!¡± state immediately after boot / left encoder button constantly ¡°pressed¡±
Inserting the controls board leads to ¡°shut down!¡± state:
I then used another power supply to supply 9V to the +12V pin and 5V to Vcc. I added the display board and the unit booted. However, when I inserted the controls PCB, the LCD would immediately show ¡°shut down!¡±.
I checked the controls board and I behaved as it should. Mainly, I ensured that pushing the left rotary encoder button connects pin 5 of the connector JP302 (PWR_ON) to ground and that releasing the button disconnects pin 5. This was the case.
When the radio was connected to the PC via USB, I could check what the processor sees in the "Diagnostics" menu: when I inserted the controls PCB, the left button was always seen as ¡°pressed¡±, which means that MOSFET Q202 is in the on state. Without the controls board inserted, everything was fine. However, simply inserting a wire into the socket of pin 5 was enough to trigger ¡°left button pressed¡± again. I also noticed that the left button state remained "pressed" for a second or so after removing the wire. Hence, I thought maybe Q202 was broken and I removed it.
Fixing the immediate ¡°shut down¡± state:
With Q202 removed, the radio never entered the ¡°shut down¡± state anymore, so I ordered a replacement. However, after replacing Q202 the problem persisted. Hence, the problem seemed to be that Q202 was activated even though the left button was not pushed and PWR_ON was not on ground level (I checked for shorts).
From the schematics I noticed that the gate of Q202 is left floating when not connected to ground. I tried to fix my problem by adding a 100K pullup resistor between the gate of Q202 and +12V, which worked. I salvaged a 100K SMD resistor from the dead 5V board (I used R108) and inserted it directly between the Gate and Source legs of Q202. Nice! The only remaining issue: when I turn the unit off (long press of left button), the "shut down" message appears, then disappears, but the display backlight stays on. I don't mind and simply remove the power supply at this point, seemingly without trouble.
Finally, I installed the new 5V SMPS board and carefully tested everything with a current limited power supply. Success, no more magic smoke and no more ¡°shut down!¡± message.
I double checked that no component legs would touch the enclosure and reinstalled everything. This time using a current limited power supply and slowly ramping the voltage from 8V to 12V, I could verify all functions of the radio and the unit has now been up and running for several hours without issues.
I don't know if I did further damage to the radio when the magic smoke escaped, and perhaps the fact that a floating gate activates a MOSFET is a sign for further trouble, but so far so good!
In any case I hope this little report will be helpful in case someone encounters similar problems.
?
Cheers,
Luke
