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WDH-930DAH Dehumidifier Repair

tjfs

New Member
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
 

tjfs

New Member
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.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
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.
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 :D
 

tjfs

New Member
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 :)
 

tjfs

New Member
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.
 

M.Joshi

Member
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.
 

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