Hello mista1,
I deeply fear that your M3 Box maybe beyond repair, due to you applying 12 volts to it. :sad:
The Ricoh (RN5T618M) marked IC does the DC to DC voltage conversion and regulation; converting
5 volts to 3.6 volts for the rest of the circuitry. Its maximum voltage input is 7 volts, but you exceeded
this by 5 volts.
I'm assuming that the original power supply you used was the 5 volt unit, but due to the Box no longer
working, you tried the 12 volt PSU in hopes that it was just the power supply (i.e. 5 volt unit) was the
cause of your Box's problem?
I doubt the unit has any over voltage protection on its input and this is why you were getting an unstable
voltage when you plugged the 12 volt supply in.
Could you please look at the picture below:
Continuity Check
What I need to get you to do is do a beep test between the green and red arrows. I want to see if this
transistor is the one that switches the input voltage into the rest of the PCB. If it does, then there should
be continuity to either the Emitter or Collector of the device.
We can continue to trouble-shoot this, but since you may have two different faults, (your original one,
and now the over-voltage one), it may be impossible to repair it. We would firstly need to assess what
part/s may have been damaged with over-voltage, but the only way of being certain, is to replace the
faulty ones. For one, you would need to replace the IC I mentioned above. But unfortunately a new one
doesn't come in the same package as your original. I don't think there would even be an adapter socket
to suit. Even if we were able to replace that IC, we still have the problem of seeing if anything else has
also been damaged, in addition, we need to find your original fault.
I really think you need to bite the bullet and write the unit off.
Sorry that I can't give you better news, but if we try to continue, it would be like flogging a dead horse.
Regards,
Relayer