I am repairing a dehumidifier which won't power on, and I've isolated the problem to missing 5v to the CPU. I found the diode which rectifies the 5v rail before the 7805 rectifier was short. Surprisingly, when I remove the bad diode and power up, I have 7.5Vac at the transformer output, so it would seem the shorted diode didn't damage anything else. With no power supplied to the unit and a 9v battery connected to the input of the 7805 via a 48 ohm series resistor the CPU powers up and displays information on the LCD, so that seems to prove the circuitry downstream.
The SMPS is a simple design with a LNK625 driving a small E16 transformer with a feedback winding and two secondaries. Both secondaries produce 7.5Vac. One output is rectified, smoothed and feeds the 7805, the other output is rectified, smoothed and goes . nowhere. I'm tempted to steal the diode from this output as it appears the same type. Probably best not to just bridge the output across as the second output winding might be lower current. The transformer is marked HS20411/E16 CQC however I can't find any information about it.
The dehumidifier is Chinese manufactured and was sold in the UK by B&Q. The power board is labelled D2514-790.
Any thoughts appreciated.
Thanks