Midea MD1001LF control board not working

[unimatrix93]

Hello everyone,

I have this high powered microwave over that does not want to start.

When I plug it in the mains power, the fan start up but the control panel does not work, no display only the stop button beeps when I press it.

I checked main filter capacitors next to the PFC IC (TNY174) they are showing 328V and the IC drain pin is at the same voltage.

The transformer has multiple outputs:

3v3, -27V, -5V, -12V.

Now when the fan is working I measure 17V on 3v3 pin and 5V when the fan stops and relay clicks. I guess it goes to standby.

Thanks in advance!

[KYBOSH]

I assume you have checked all the capacitors (for both capacitance and ESR), resistors, diodes and octocouplers right?
The boards looks discolored on the right side of the transfomer. Everything okay over there?

[unimatrix93]

I assume you have checked all the capacitors (for both capacitance and ESR), resistors, diodes and octocouplers right?
The boards looks discolored on the right side of the transfomer. Everything okay over there?

I checked every resistors, diodes and the two octocouplers. I measured the capacitance of the caps but I don't have an ESR meter sadly.
I found a silicone diode next to the transformer which measures 2.4v on forward bias and OL on reverse bias.
I even desoldered the display to check under it, but everything there is also looks good.

[KYBOSH]

So as soon as you plug the microwave to the mains the fan automatically kicks on? That very strange.
What happens if you disconnect the magnetron from the circuit board?

[lotas]

Check the keyboard, one of the navigation buttons may be short...