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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

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Old 25th May 2017, 12:01 am   #41
paulsherwin
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Default Re: Ancient microwave oven - repairable?

Proper commercial microwaves are still expensive and complex things, with several magnetrons to penetrate the food evenly. Domestic models just heat the outer half inch or so of the food and steam the rest. That's all you need to heat up a mug of soup or tin of baked beans of course.
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Old 25th May 2017, 12:26 am   #42
threeseven
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Default Re: Ancient microwave oven - repairable?

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Originally Posted by julie_m View Post
I'm a bit surprised no-one ever tried fitting a magnetron with a grid for power control purposes .....
Yes, power control on my 1989 Panasonic, a high end model at the time, is just by turning the magnetron on and off, the lower the power the longer it's off to on time ratio.
Not an effective method for shorter cooking times.
The newer inverter types do have proper proportional power control.
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Old 25th May 2017, 7:50 am   #43
Dave Moll
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Default Re: Ancient microwave oven - repairable?

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Originally Posted by paulsherwin View Post
... to heat up a ... tin of baked beans of course.
Leaving the tin outside, of course!
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Old 25th May 2017, 9:08 am   #44
Malcolm G6ANZ
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Default Re: Ancient microwave oven - repairable?

Due to the way magnetrons work it is impossible to put a grid in one to control the power. They work by spiralling electrons in a magnetic field until they hit a resonant cavity and the RF is extracted from a cavity by means of an aerial.
The way to reduce or control power is to change the pulse rate at which they are fired or to alter the HT voltage on them.
The best history and description of a magnetron is here http://www.johnhearfield.com/Radar/Magnetron.htm
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Old 25th May 2017, 11:55 am   #45
steve1010uk
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Default Re: Ancient microwave oven - repairable?

Ages ago i completed the RETRA microwave course, thirst thing we were taught was the 3 "D"s,

Disconnect (unplug it) Door (open it just in case some idiot plugs it back in again) Discharge ( short out the high voltage cap with a well insulated screwdriver)

Most faults on the H/V side can be diagnosed with a multimeter set on ohms range with no need to apply power.

When working on the mains side of the transformer i always disconnected the spade terminal feeding mains to the transformer and tucked it out of the way that way no H/V to worry about,

Many faults were caused by dodgy door interlock switches, these can be opened up to check for pitting on the contacts or the lamp failing and blowing the fuse (easy money)

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Old 9th Jun 2017, 4:16 pm   #46
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Default Re: Ancient microwave oven - repairable?

In the course of trying to repair my microwave, I made up a discharging lead - two probes connected by wires and a 1k ww 5watt resistor - all well insulated by heatshrink. After turning off unplugging and opening the door you'd shove the probes down the cap terminal boots - go and have a cup of tea - then come back and check all was earthed/charge gone. Turned out eht rec was shot and it was cheaper to buy a new oven. Still have the old oven somewhere and it will become a small paint spray cabinet soon - thanks to the turntable.
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