WDH-930DAH Dehumidifier Repair

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 /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

Why not just replace the faulty diode?. It seems a bit bizarre that they would have the components fitted for an output that's doing nothing.

I have ordered a replacement diode, should arrive next week. I agree it's very strange they fitted those components if they don't do anything.

tjfs said:

I have ordered a replacement diode, should arrive next week. I agree it's very strange they fitted those components if they don't do anything.

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Any small fast recovery rectifier should be fine - back when I used to repair TV's etc. I had two draws labelled:

Small fast diodes

Large fast diodes

They used to cover almost all my needs

I think these were five for under £2 delivered for an exact replacement, so that's fine.

Still no idea why the second output has those apparently redundant components on it

An update - the diodes finally arrived, I fitted one in place of the shorted component and everything works as it should now.

Presumably the LNK SMPS IC protected everything when the diode went short.

You may find that the capacitor(s) used for smoothing the output after the rectifier isn't doing its job properly and probably needs replacing.

That may be the cause of the shorted diode. Probably advisable to replace the capacitor on the output of the 7805 too.

Another reason may be excessive current draw from the circuitry fed from the 7805.