deloghi dehumidifier compressor not switching on

I suspect my dehumidifier has much the same problem as this one: https://www.google.co.uk/?gws_rd=ssl#safe=off&q=lisheng+lrd+s+124+dmt
Trouble is I don't understand what he says the cure is, is it the capacitor needs replacing or the yellow capacitor?
Compressor works fine when switched by the fan relay.
AJH
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     snipped-for-privacy@loampitsfarm.co.uk writes:

Try describing the problem, rather than pointing to a page of google search results.

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Andrew Gabriel
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On Sat, 12 Dec 2015 16:27:13 -0000 (UTC), snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

My apologies, I intended to provide the link to a you tube video in german

https://www.youtube.com/watch?v=ijMhvP3jvTc

Which shows the control circuit.
The dehumidifier has both a fan to circulate air through the evaporator coil and condenser coil, which are in series, and a ordinary hermetically sealed refrigerator compressor.
When powered the fan runs, controlled by one of two identical relays. The compressor does not run and it is controlled by the other relay. I have swapped terminals for the fan and compressor, then the compressor runs, the evaporator gets cold and the condenser coil gets hot. So my guess was one of the relays had failed.
The german video appears to say he has the same problem of the compressor not running but he has removed a capacitor from the circuit.
AJH
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     snipped-for-privacy@loampitsfarm.co.uk writes:

That's the voltage dropper from mains to LV for the control logic supply. I would not expect either relay to work if that was dead. Measuring the LV supply voltage would confirm if the dropper PSU is working. IME, when those dropper PSU's fail, it's normally the power resistor in series with the capacitor which dies, although I have had one case of the zenor diode which does the (crude) voltage regulation failing.
Look very carefully (with a magnifying glass) at the compressor relay soldered joints. Sometimes, you can get hairline fractures caused by vibration from the relay operating and lead-free solder. However, more likely is that some sensor which gates the compressor running (or its associated logic) has gone faulty. There's usually a timer delay on the compressor starting up (3 mins on mine) to ensure there's no residual pressure difference left in the system from the previous run, as that will prevent the compressor starting (they have only just enough starting torque to work when the system has no residual pressure differential, and will not be able to start if there is any).
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Andrew Gabriel
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On Sat, 12 Dec 2015 18:27:19 -0000 (UTC), snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote: Firstly Thank you Graham and Andrew for your replies.
Would a symptom of this failed capacitor take a few moments to appear? Because the fan solenoid clicks in and holds as soon as powered on but a slight tap and it drops out.
I am having trouble measuring voltage across the capacitor, what is its function, smoothing? it's difficult to make a good contact but the digital meter won't settle, ranging from 0-16V, the moving coil seems to read above 2.5V and below 10V.
Solder joints look fine and shiny.

This makes sense, my 2kW compressor won't start off my 4kVA genset if there is any pressure in the reservoir.
So the logic on start will be run fan to bring air over the humidity sensor, not start compressor for 3 minutes to allow residual pressure to drop and stop compressor if evaporator coil drops below freezing?
Then sensors to stop on low humidity and high water level.
AJH
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     snipped-for-privacy@loampitsfarm.co.uk writes:

If the dropper circuit is not supplying enough current to the LV circuitry, this might well happen. It would be interesting to measure the LV supply voltage. You can probably get an idea what it should be from the coil voltage rating of the relays (probably 12, 24, or 48V). Look for an electrolytic capacitor with a higher voltage rating, and measure the DC voltage across that. Note that although this is low voltage, it is coupled directly to the mains, and must be treated as live mains from the safety point of view.

That capacitor will have most of the mains voltage across it, and it will be AC which is why your meter can't get a sensible DC reading.

and possibly on frozen condensation on the evaporator, and/or inlet air temperature being outside an allowable range.
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Andrew Gabriel
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On Sun, 13 Dec 2015 13:44:26 -0000 (UTC), snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

Relays are 125V ac and 28V dc.
Two electrolytic capacitors 470 micro Farad and 35V, one with 4.5V and the other 6 V but my hands are a bit unsteady. Two Zener diodes in parallel with 4.6V across them.
AJH
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     snipped-for-privacy@loampitsfarm.co.uk writes:

Those sound like the contact rating, rather than the coil rating.

That sounds low, given the 35V capacitor rating. It could be that the mains dropper capacitor has reduced in value. Other options would the the large resistor near it having increased in value, or the zenors failed, or some other component is drawing too much current from the LV supply. If there's anything written on the zenor diodes, that would be interesting.
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On Sun, 13 Dec 2015 15:18:09 +0000, snipped-for-privacy@loampitsfarm.co.uk wrote:

After a bit of a wait for 5 capacitors to arrive from Hong Kong I soldered in a new one and everything is working for an outlay of £1.99 thanks to a search on the web and help from here.
I suspect many white goods like this end up scrapped from small faults. Indeed pre interweb I would have had to buy a complete control board for £35 to fix this.
AJH
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On Sun, 07 Feb 2016 10:49:02 +0000, snipped-for-privacy@loampitsfarm.co.uk wrote:

Result! ;-)

Yup. Luckily, some people are sensible enough to put such things on the likes of Freecycle (or even eBay) so that those of us willing to 'give things a go / look' might get them running again. Like the 13 month old washing machine that was written off as 'uneconomic to repair', that we repaired (cheaply) and used for another 7+ years or the Dyson cylinder cleaner that just needed the plug cutting off the broken mains lead and a new plug fitting. ;-)

But even that would have probably been better than throwing the whole thing away?
Yesterday I changed two blown caps on a PC video card but on the first test it doesn't seem to have helped, but as you say for the cost, it always seems worth a go. ;-)
Cheers, T i m
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On Sat, 12 Dec 2015 16:27:13 -0000 (UTC), snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

He is probebly referring to this.
https://www.youtube.com/watch?v=ijMhvP3jvTc

Looks like a 1uF wattless dropper goes low capacitence causing the LT rail to drop in voltage.
To the OP, if you replace this capacitor, ensure it is "X rated" it's a safety critical component.
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Graham.

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