How does it work

[Satinseat]

Hope you allow us nobodies to ask for your help with an electronic problem.
If so can you explain why a remote control socket is suddenly faulty. When switched on (by hand or remote) there is a flash of power to the output but then nothing. To the dumb like me seems something is not locking on.
If this is not allowed have a happy Easter anyway.
Thanks ian

 

[Diver300]

A remote control socket contains:-
1) A power supply to create a low voltage from the mains, much like a phone charger.
2) A radio receiver, which runs from the low voltage and also can turn on and off the low voltage.
3) A relay, which is a switch operated by a low-voltage electromagnet. It is that switch which actually controls the power to what you have plugged in.

The relay will need the low voltage going to it continually for the output socket to be on.
Any of the items that I have listed can go wrong.
The symptom that you have mentioned could be due to the power supply part becoming weak. By that I mean that it work OK with low loads, but not with a full load. It may be able to run the radio receiver, but not have enough power to run the relay as well. (A bit like a flat car battery, where the car can be unlocked, the dashboard lights come on, but everything turns off when you try to start the car).
The weak power supply means that when the radio receiver tries to turn on the relay, there isn't enough power to keep the relay running, and the voltage to the radio receiver is interrupted, and the radio receiver turns off. That turns the relay off. The voltage gets back up to normal, and the radio receiver starts working again, but with nothing to make it remember that the relay had been turned on, the radio receiver starts up with the relay turned off.

Any component can just spontaneously fail. However, a likely cause would be an electrolytic capacitor. Those are used in power supply circuit and they degrade with time, much faster if they are hot. A weak electrolytic capacitor will often cause the power supply to be weak.

 

[Satinseat]

Thanks for that, understood most of it as it was clearly explained.
How do I recognise the capacitor, know what to buy if it can be replaced or is is like a car fault where you replace different parts till it works again.

 

[cpprioli]

Capacitors that have failed due to heat, as has been suggested above, will often exhibit a visible amount of swelling, most often apparent at the upper end cap of radial electrolytic capacitors. These devices will have the appearance of bulging, and you may even observe splitting of the break lines on the capacitor end. Look also for leakage of electrolyte from failed caps.

Often, there will be no apparent fault in a cap, and then the only real means of determining whether the cap has failed is to measure its equivalent series resistance (ESR), which is done through the use of an ESR meter.

 

[Diver300]

If you google images for "electrolytic capacitor", you'll see what they look like.

If you can get to the circuit, and can solder, you can change just the capacitors. That can be done on car modules, but car mechanics don't generally change anything smaller than a complete module.

The voltage rating (in V) and capacitance (in μF) is written on electrolytic capacitors. You can always use a larger voltage rating than the original, and in most circuits having a larger capacitance is better. The voltage rating is the maximum, not the expected. It's not like a battery, where it has to run at about the right voltage to be any good at all. It is more like a pressure vessel, where there is a maximum safe pressure, but it can be used at any pressure up to that.

The larger the voltage rating and the larger the capacitance, the larger the physical size, so that often limits the new one to the same rating as the previous one.

Make sure you put replacement in the same way round. The direction is often marked on the board, but photograph it before you start. Getting them the wrong way round usually ends up with them bursting.

Some multimeters will read the capacitance, but it isn't always a good indication of if they have failed, but a capacitor reads a lot less than its rating, it's dead. You may need to remove the capacitor from the circuit to measure the capacitance or the ESR.

If nothing else is obviously wrong, changing all the electrolytic capacitors can be a way of fault-finding, as they are about the only components that will degrade with time. They degrade much faster if hot. If the capacitors need to be removed to be tested, it's often easier to replace with new ones.

 

[Nigel Goodwin]

Some multimeters will read the capacitance, but it isn't always a good indication of if they have failed, but a capacitor reads a lot less than its rating, it's dead. You may need to remove the capacitor from the circuit to measure the capacitance or the ESR.

It's generally pointless measuring their capacitance, as by FAR the most common failure is high ESR, with the capacitance still remaining within specification. With an ESR meter you can almost always check them in circuit as well, which makes for a very easy way to test them.

If you have an oscilloscope (but not an ESR meter) you can also check the ripple on the capacitor, which will be excessive if the capacitor is high ESR - this is often easier than an ESR meter, as you can usually do it without removing the PCB.

One caveat about capacitors and ESR, high voltage ones (100-200V upwards) tend to check high ESR anyway, even when new, compared with low voltage ones of the same capacitance.

I agree that blanket replacement of electrolytics (in vulnerable places) is often a very good technique - even if you find some faulty ones, it's a good idea to change those that still check OK, as they are likely to fail in the near future.

 

[dr pepper]

Might be worth checking the outputsocket recepticles, imported stuff tends to be copper coated steel, and steel can relax over time leaving a losse connection.