Microwave safe with power and cover off?

[minermick]

The knob on the manual rotating timer of my microwave has come loose and before it goes completely I thought I would take of the cover and see if it is repairable.
If the knob is of the type that is held on to a spindle/shaft by a grub type screw then it may be easily repaired, but from what i`ve read on this forum i`m unsure if there could still be power inside the unit even with the power completely disconnected.
I have a lot of work experience of H & S and diy experience but I`m unsure of this.
Do microwaves/magnetrons hold power when not in use and if so for how long?

 

[OwainDIYer]

the power supply capacitors can store thousands of volts for several hours. There are also dangers associated with disturbing seals and interlocks.

Unless you are skilled in EHT work I would strongly advise to leave well alone - a new cheapy is under £30.

 

[captaincaveman1]

A capacitor within the appliance store's a charge of at least 2000 volts an engineer is trained on how to discharge this safely so the appliance can be worked on your not so dont even think about it . In november 2012 a contractor for Marks & Spencer tried to have a go at repairing the microwave in one of the store's canteen's it killed him outright.

 

[olly_k]

The fact you have to ask this should tell you your answer. It is not so much the voltage, but a combination of the high voltage and high current that the transformer / capacitors can provide. The high current means that unlike for instance a taser, which will significantly drop in volts from 50,000 to maybe a couple of hundred on contact, a microwave power supply will not, and you will turn to toast, maybe the one time a microwave does a good job at that particular snack!

Seriously IT WILL KILL YOU if you make a mistake no questions.

 

[Jackrae]

Not for me to tell you what to do but scare mongering does no-one any use.

Usually the HV capacitor in a microwave is in series with the AC output of the HT transformer in the feed line to the magnetron. This type of capacitor also usually has either an internal or external bleed resistor across its terminals for the sole purpose of eliminating charge retention.

If the AC power cable is removed from the wall socket and the microwave has not been used for at least an hour then the chance of there being any voltages running around waiting to surprise you is virtually nil.

Within the casing of the unit you may well find the circuit diagram. This will verify if the capacitor is in series with the transformer and if there is a fitted or in-built bleed resistor. Either way, time is your friend.

Only capacitors store energy - transformers need input power to give outputs.

NEVER operate the unit with the casing off. Too many volts and possibly RF transmissions flying around.

 

[captaincaveman1]

Not for me to tell you what to do but scare mongering does no-one any use.

(Try telling that to the person killed in november as that microwave had not been used for a period of time.)

Qoute jackrae
Usually the HV capacitor in a microwave is in series with the AC output of the HT transformer in the feed line to the magnetron. This type of capacitor also usually has either an internal or external bleed resistor across its terminals for the sole purpose of eliminating charge retention.

(Only in recent years have these been fitted.)

Qoute jackrae
If the AC power cable is removed from the wall socket and the microwave has not been used for at least an hour then the chance of there being any voltages running around waiting to surprise you is virtually nil.



The fact is people have been killed by trying to work on them so im not scare mongering in anyway !!!

 

[olly_k]

Not for me to tell you what to do but scare mongering does no-one any use.

Usually the HV capacitor in a microwave is in series with the AC output of the HT transformer in the feed line to the magnetron. This type of capacitor also usually has either an internal or external bleed resistor across its terminals for the sole purpose of eliminating charge retention.

If the AC power cable is removed from the wall socket and the microwave has not been used for at least an hour then the chance of there being any voltages running around waiting to surprise you is virtually nil.

Within the casing of the unit you may well find the circuit diagram. This will verify if the capacitor is in series with the transformer and if there is a fitted or in-built bleed resistor. Either way, time is your friend.

Only capacitors store energy - transformers need input power to give outputs.

NEVER operate the unit with the casing off. Too many volts and possibly RF transmissions flying around.

Having worked on tellies in the past I can tell you bleed resistors can fail high - it is not good enough to assume the capacitor will discharge over hours or days, if there is any doubt, don't mess about!

Besides I would not want to encourage the OP or any one else not experienced or trained for fear of appearing in court.

So just to repeat, do NOT open or otherwise play with any high voltage equipment if you do not know exactly what you are doing![/b]