Re: QMX rev 2 build dead and does not boot
|
What is puzzling me is that Frans reports seeing 12V at Q103 and Q105 but not at the input of the 78m33 regulator.
It is as if there is a fault of some kind at Q101/R101 that is preventing Q102 from turning on.
Frans, with power turned off, can you measure the resistances at Q101: gate to source, gate to drain, drain to source ? ? JZ
JZ
Evan, Frans,
Frans, first my thanks for a clear and concise response. It is very helpful.
Evan, take a look at Frans' description again , and the schematic, too.
....
Q103 en Q105 pin 1 and 3 I measure 12 volt
on the switch I measure 12 volt on 1 side an 0 on the otherside of the switch
If I press the switch both pins become 0 volt and i see a small cuurent is drown form the PSU
but no voltage on the 78m33 stil all pins stay 0
...
Could a failed D101 diode or a bad solder?joint there be responsible?for what Frans is seeing??
JZ ? On Sun, Dec 31, 2023, 7:52?AM Evan Hand < elhandjr@...> wrote: Hello Frans,
The 12 volts feeding the 78M33 comes from the Plug-in PCB #1 (5 volt SMPS board).? Pressing the left encoder grounds the "PWR_ON" flag, which turns on Q103 and Q105 while holding the button.? "PWR_HOLD" comes from the MPU to turn the two transistors on through Q104.? What is not happening is the MPU is not turning on that signal.
I had your symptoms with my first QMX build.? This was after I found a problem with the control board and tried to diagnose it while exposed on the bench.? I somehow damaged the MPU during testing, and that kit is now spare parts.?
Try removing both SMPS boards, the display, and the control board.? Verify the resistance of Vdd to ground on the main board.? For my failed unit, it was 0 Ohms.? I had fried the MPU.
I hope you do not have the same problem; replacing the MPU or scrapping the kit are the only choices.? Hans may make the MPU with his proprietary bootloader available for those capable of replacing the MPU.? I have not yet seen that offer on the web.
73
Evan
AC9TU
|
