So it was making an odd noise, and not heating the food, light comes on,
steel turntable revolves, beeper sounds at end of cook time.

Check HV fuse. Blown. Aha, replaced, it's done that before, should be
OK... but no! Food still cold, fuse blown again.


Check the diode (CL04-12) using a multimeter on 20V setting and 9V
(actually 8.34V) battery. 0V one way, 3.26 the other. A bit low?

Capacitor: No connection (meter on 2000k ohms setting) between either
terminal and case. Between terminals resistance increases from zero to
infinity over a second or so.

Magnetron: Meter set to 200 ohms. 0.5 ohms between terminals either way.
Meter set to 2000kohms, no connection between terminals and case.

High voltage transformer: Primary, isolated, about 2.2 ohms. Secondary
150. There is another winding that seems to go to the magnetron, I don't
know what this is.


So any help on what's up, and what to do about it?

On Fri, 14 May 2021 13:31:48 +0100, Chris Bacon wrote:

So it was making an odd noise, and not heating the food, light comes on,
steel turntable revolves, beeper sounds at end of cook time.

Check HV fuse. Blown. Aha, replaced, it's done that before, should be
OK... but no! Food still cold, fuse blown again.


Check the diode (CL04-12) using a multimeter on 20V setting and 9V
(actually 8.34V) battery. 0V one way, 3.26 the other. A bit low?

Capacitor: No connection (meter on 2000k ohms setting) between either
terminal and case. Between terminals resistance increases from zero to
infinity over a second or so.

Magnetron: Meter set to 200 ohms. 0.5 ohms between terminals either way.
Meter set to 2000kohms, no connection between terminals and case.

High voltage transformer: Primary, isolated, about 2.2 ohms. Secondary
150. There is another winding that seems to go to the magnetron, I don't
know what this is.


So any help on what's up, and what to do about it?


Try another magnetron.

On 14/05/2021 13:31, Chris Bacon wrote:
So it was making an odd noise, and not heating the food, light comes on,
steel turntable revolves, beeper sounds at end of cook time.

Make and model ?

On 14/05/2021 14:47, Andrew wrote:
On 14/05/2021 13:31, Chris Bacon wrote:
So it was making an odd noise, and not heating the food, light comes
on, steel turntable revolves, beeper sounds at end of cook time.

Make and model ?

Crikey. It's a Bifinett KH1167, which I think was also badged Silverline
at one time.

On 14/05/2021 14:50, Chris Bacon wrote:
On 14/05/2021 14:47, Andrew wrote:
On 14/05/2021 13:31, Chris Bacon wrote:
So it was making an odd noise, and not heating the food, light comes
on, steel turntable revolves, beeper sounds at end of cook time.

Make and model ?

Crikey. It's a Bifinett KH1167, which I think was also badged Silverline
at one time.

Ahh. Not many had metal turntables like my Sharp did. That suddenly
stopped heating on microwave but worked fine on oven and/or grill.
Luckily, I was in the BHF charity shop in Worthing and they had a
almost-unused Panny CT552 combi-microwave for £30 which works fine,
so the 20KG Sharp lump is heading for the recycling skip.

The Panny has a much nicer and quieter beep, beep, beep at completion.
The sharp had a really annoying piezo-electric buzzer that sounded
for too long.

On 14/05/2021 13:31, Chris Bacon wrote:
So it was making an odd noise, and not heating the food, light comes on,
steel turntable revolves, beeper sounds at end of cook time.

Check HV fuse. Blown. Aha, replaced, it's done that before, should be
OK... but no! Food still cold, fuse blown again.


Check the diode (CL04-12) using a multimeter on 20V setting and 9V
(actually 8.34V) battery. 0V one way, 3.26 the other. A bit low?

Capacitor: No connection (meter on 2000k ohms setting) between either
terminal and case. Between terminals resistance increases from zero to
infinity over a second or so.

Magnetron: Meter set to 200 ohms. 0.5 ohms between terminals either way.
Meter set to 2000kohms, no connection between terminals and case.

High voltage transformer: Primary, isolated, about 2.2 ohms. Secondary
150. There is another winding that seems to go to the magnetron, I don't
know what this is.


Magnetron filament winding, connected to the two magnetron terminals.
Disconnect at the magnetron and check that this transformer winding and
the magnetron filament are OK (fraction of an ohm - but not zero). One
side of the filament circuit will be connected to the diode's anode. The
other magnetron connection (its anode) is via the magnetron's body. The
transformer HV secondary should have one end connected to the
transformer body, the current path between this and the magnetron anode
being via the chassis.

A blown filament shouldn't blow a fuse, though. Slightly worrying that
the fuse has blown before !

PA

On 14/05/2021 15:40, Peter Able wrote:
On 14/05/2021 13:31, Chris Bacon wrote:
High voltage transformer: Primary, isolated, about 2.2 ohms. Secondary
150. There is another winding that seems to go to the magnetron, I
don't know what this is.


Magnetron filament winding, connected to the two magnetron terminals.
Disconnect at the magnetron and check that this transformer winding and
the magnetron filament are OK (fraction of an ohm - but not zero). One
side of the filament circuit will be connected to the diode's anode. The
other magnetron connection (its anode) is via the magnetron's body.Â* The
transformer HV secondary should have one end connected to the
transformer body, the current path between this and the magnetron anode
being via the chassis.

Thank you. OK, I disconnected at the magnetron, and there seems to be a
tiny resistance through the few red/black flecked fabric-covered coils I
can see in the middle of the transformer. Maybe 0.1 ohm, but my meter
isn't particularly precise.

Is there anything else to measure?


A blown filament shouldn't blow a fuse, though.Â* Slightly worrying that
the fuse has blown before !

It's quite an old machine now, and I have heard that the fuses can go
after repeated uses.... coincidentally, I had just used "low power"
to simmer things; this seems to be full power but switched on and off
every so often....

On 14/05/2021 16:13, Chris Bacon wrote:
On 14/05/2021 15:40, Peter Able wrote:
On 14/05/2021 13:31, Chris Bacon wrote:
High voltage transformer: Primary, isolated, about 2.2 ohms.
Secondary 150. There is another winding that seems to go to the
magnetron, I don't know what this is.


Magnetron filament winding, connected to the two magnetron terminals.
Disconnect at the magnetron and check that this transformer winding
and the magnetron filament are OK (fraction of an ohm - but not zero).
One side of the filament circuit will be connected to the diode's
anode. The other magnetron connection (its anode) is via the
magnetron's body.Â* The transformer HV secondary should have one end
connected to the transformer body, the current path between this and
the magnetron anode being via the chassis.

Thank you. OK, I disconnected at the magnetron, and there seems to be a
tiny resistance through the few red/black flecked fabric-covered coils I
can see in the middle of the transformer. Maybe 0.1 ohm, but my meter
isn't particularly precise.

Is there anything else to measure?


A blown filament shouldn't blow a fuse, though.Â* Slightly worrying
that the fuse has blown before !

It's quite an old machine now, and I have heard that the fuses can go
after repeated uses.... coincidentally, I had just used "low power"
Â*to simmer things; this seems to be full power but switched on and off
every so often....

OK. Do you mean that you've replaced the fuse and can use the lower
power mode for ever - but when you try full power it fails and blows the
fuse? If so, how long does it run full power before it fails.

Has the microwave been stored in a garage? That can result in
transformer damage when powered up?

PA

On 14/05/2021 18:00, Peter Able wrote:

OK. Do you mean that you've replaced the fuse and can use the lower
power mode for ever - but when you try full power it fails and blows the
fuse?Â* If so, how long does it run full power before it fails.

I've only just learned how to use low power (which seems to me to be
merely full power applied in short on/off bursts)! I was only
speculating that having the thing switch itself on and off a few times a
minute might affect fuse life were it used often... but:

This thing has been in regular use for ages. The fuse blew probably
yesterday on "normal" the full power setting. I changed the fuse today,
having noticed it was not heating my breakfast, and the replacement blew
probably straight away, certainly within a second or two, I don't know
how to measure that, but it did not noticably heat up my cold coffee.

I have no evidence at all that it works on "low power" (see para. 1).

Has the microwave been stored in a garage?Â* That can result in
transformer damage when powered up?

No, it has been on the worktop in my kitchen, as I say in general use,
certainly daily.


I wondered again about the diode. I am certainly no expert, but I know
what a diode does (but not in context). Testing it again, but on an old
12V battery, gives me no throughput one way, but a 7.93V potential the
other way (off a 13.2V battery).

On 14/05/2021 13:31, Chris Bacon wrote:
So it was making an odd noise, and not heating the food, light comes on,
steel turntable revolves, beeper sounds at end of cook time.

Check HV fuse. Blown. Aha, replaced, it's done that before, should be
OK... but no! Food still cold, fuse blown again.

Do you mean the fuse in series with the transformer, ie 230V?

Check the diode (CL04-12) using a multimeter on 20V setting and 9V
(actually 8.34V) battery. 0V one way, 3.26 the other. A bit low?

This may be a number of diodes in series, so 5V drop may be expected.

Capacitor: No connection (meter on 2000k ohms setting) between either
terminal and case. Between terminals resistance increases from zero to
infinity over a second or so.

Sounds good. If it was o/c there would be no HV power getting to the
magnetron.

Magnetron: Meter set to 200 ohms. 0.5 ohms between terminals either way.
Meter set to 2000kohms, no connection between terminals and case.

I assume 0.5 ohms refers to the cathode heater, which sounds ok.

The case is the anode, ie at ground potential.

High voltage transformer: Primary, isolated, about 2.2 ohms. Secondary
150. There is another winding that seems to go to the magnetron, I don't
know what this is.

There should be 2 wires to the magnetron heater from the transformer,
one wire will be attached to the HV generator.

Initially I thought 2.2 ohms sounded very low, but the ratio between
primary and secondary is consistent with 2kV output. ie a square function.

So any help on what's up, and what to do about it?

If you disconnect hot side of the secondary and turn it on, does the
fuse still blow?

Do take care. There is a lethal amount of energy at a lethal voltage in
a microwave.

Chris Bacon wrote:
On 14/05/2021 18:00, Peter Able wrote:

OK. Do you mean that you've replaced the fuse and can use the lower
power mode for ever - but when you try full power it fails and blows
the fuse? If so, how long does it run full power before it fails.

I've only just learned how to use low power (which seems to me to be
merely full power applied in short on/off bursts)! I was only
speculating that having the thing switch itself on and off a few times a
minute might affect fuse life were it used often... but:

This thing has been in regular use for ages. The fuse blew probably
yesterday on "normal" the full power setting. I changed the fuse today,
having noticed it was not heating my breakfast, and the replacement blew
probably straight away, certainly within a second or two, I don't know
how to measure that, but it did not noticably heat up my cold coffee.

I have no evidence at all that it works on "low power" (see para. 1).

Has the microwave been stored in a garage? That can result in
transformer damage when powered up?

No, it has been on the worktop in my kitchen, as I say in general use,
certainly daily.


I wondered again about the diode. I am certainly no expert, but I know
what a diode does (but not in context). Testing it again, but on an old
12V battery, gives me no throughput one way, but a 7.93V potential the
other way (off a 13.2V battery).

Is it possible the diode is actually made of diodes in series ?

*******

CL01-12 Diode Microwave Oven High Voltage 12kV 350MA

12kV repetitive peak reverse
350mA average output forward
30A surge, 8.3msec, forward
Vf 12V max at 350mA --- about 12 diodes in series or so
at roughly 1V drop on each, cannot be
checked on "diode" range of multimeter
2 to 50ua reverse leakage

You would need to make up a little test circuit
to verify the forward characteristic.

Paul

On Fri, 14 May 2021 13:31:48 +0100, Chris Bacon wrote:

So it was making an odd noise, and not heating the food, light comes on,
steel turntable revolves, beeper sounds at end of cook time.

Check HV fuse. Blown. Aha, replaced, it's done that before, should be
OK... but no! Food still cold, fuse blown again.


Check the diode (CL04-12) using a multimeter on 20V setting and 9V
(actually 8.34V) battery. 0V one way, 3.26 the other. A bit low?

Capacitor: No connection (meter on 2000k ohms setting) between either
terminal and case. Between terminals resistance increases from zero to
infinity over a second or so.

Magnetron: Meter set to 200 ohms. 0.5 ohms between terminals either way.
Meter set to 2000kohms, no connection between terminals and case.

High voltage transformer: Primary, isolated, about 2.2 ohms. Secondary
150. There is another winding that seems to go to the magnetron, I don't
know what this is.


So any help on what's up, and what to do about it?

I had something similar and it turned out to be the magnetron breaking
down under load.

On 15/05/2021 05:59, jon wrote:

So any help on what's up, and what to do about it?

I had something similar and it turned out to be the magnetron breaking
down under load.

I've got one on order, plus 10 fuses....

On 15/05/2021 01:02, Paul wrote:
Is it possible the diode is actually made of diodes in series ?

*******

CL01-12 Diode Microwave Oven High Voltage 12kV 350MA

12kV repetitive peak reverse
350mA average output forward
30AÂ*Â* surge, 8.3msec, forward
Vf 12V max at 350mAÂ*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* --- about 12 diodes in series or so
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* at roughly 1V drop on each, cannot be
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* checked on "diode" range of multimeter
2 to 50ua reverse leakage

You would need to make up a little test circuit
to verify the forward characteristic.


No idea. It's a CL04-12 if that makes a difference. I don't know what a
test circuit would be.

Yes Magnetrons can flash over and fail. Usually they get air in, or get
carbonised somewhere, however when I could see the usual suspects were the
transformer or the diode.
Some of the more complexes ones with a lot of electronics can just fry
their control boards, sadly, Toshiba were good at that.
Brian

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"jon" wrote in message ...
On Fri, 14 May 2021 13:31:48 +0100, Chris Bacon wrote:

So it was making an odd noise, and not heating the food, light comes on,
steel turntable revolves, beeper sounds at end of cook time.

Check HV fuse. Blown. Aha, replaced, it's done that before, should be
OK... but no! Food still cold, fuse blown again.


Check the diode (CL04-12) using a multimeter on 20V setting and 9V
(actually 8.34V) battery. 0V one way, 3.26 the other. A bit low?

Capacitor: No connection (meter on 2000k ohms setting) between either
terminal and case. Between terminals resistance increases from zero to
infinity over a second or so.

Magnetron: Meter set to 200 ohms. 0.5 ohms between terminals either way.
Meter set to 2000kohms, no connection between terminals and case.

High voltage transformer: Primary, isolated, about 2.2 ohms. Secondary
150. There is another winding that seems to go to the magnetron, I don't
know what this is.


So any help on what's up, and what to do about it?


Try another magnetron.

There is no such thing as low power on a Magnetron, they simply put it on
and off to simulate the lower energy over time so to speak.

Is the filament reading OK?

Also, I was intrigued by the diode being such a poor conductor in one
direction, in your previous post. However as you have not actually killed
yourself yet, my guess is there is no eht for whatever reason.
Brian

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"Chris Bacon" wrote in message
...
On 14/05/2021 15:40, Peter Able wrote:
On 14/05/2021 13:31, Chris Bacon wrote:
High voltage transformer: Primary, isolated, about 2.2 ohms. Secondary
150. There is another winding that seems to go to the magnetron, I don't
know what this is.


Magnetron filament winding, connected to the two magnetron terminals.
Disconnect at the magnetron and check that this transformer winding and
the magnetron filament are OK (fraction of an ohm - but not zero). One
side of the filament circuit will be connected to the diode's anode. The
other magnetron connection (its anode) is via the magnetron's body. The
transformer HV secondary should have one end connected to the transformer
body, the current path between this and the magnetron anode being via the
chassis.

Thank you. OK, I disconnected at the magnetron, and there seems to be a
tiny resistance through the few red/black flecked fabric-covered coils I
can see in the middle of the transformer. Maybe 0.1 ohm, but my meter
isn't particularly precise.

Is there anything else to measure?


A blown filament shouldn't blow a fuse, though. Slightly worrying that
the fuse has blown before !

It's quite an old machine now, and I have heard that the fuses can go
after repeated uses.... coincidentally, I had just used "low power"
to simmer things; this seems to be full power but switched on and off
every so often....

But assuming its not some computer controlled device, there is very little
to go wrong, so it might be a simple repair.
Brian

--

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Note this Signature is meaningless.!
"Jethro_uk" wrote in message
...
Funny to see this post, as our 15 year old microwave packed up two days
ago. Went to take the beans out and they were still cold

Light and turntable work (obviously - hence my surprise at cold beans).
But at 15 years in there's no point considering anything other than a
replacement.

On 15/05/2021 08:57, Brian Gaff (Sofa) wrote:
There is no such thing as low power on a Magnetron, they simply put it on
and off to simulate the lower energy over time so to speak.

Is the filament reading OK?

Also, I was intrigued by the diode being such a poor conductor in one
direction, in your previous post. However as you have not actually killed
yourself yet, my guess is there is no eht for whatever reason.

Why do you think I might kill myself?


The filament reads "almost no resistance", if you mean the "winding" on
the transformer, the terminals on the magnetron connedct to each other
with very low resistance, but not to the case.

A new diode costs only a couple of pounds so I may get one of those as
well as the magnetron & fuses I have on order.

Inverter microwave power supplies are effectively continuous at the
power selected. They don't switch on/off in the way that conventional
power supplies do, although they do use pulse-width modulation to
control the power.

This is from http://educypedia.karadimov.info/library/Inverter.pdf
"Inverter Technology In inverter-equipped microwave ovens, the power
transformer is replaced by a circuit board, which converts the 60Hz
incoming line frequency to a variable rate of 20 KHz to 45 KHz. A
relatively small transformer is then required to increase the voltage to
the level required by a magnetron. By varying the pulse width, the
output power can be linearly controlled for more precise cooking and
defrosting levels. The bulky power transformer is replaced by a small,
lightweight circuit board; and, because less heat is dissipated, power
efficiency is increased. Conventional technology uses just a single
power level, which is regulated by switching pulses. In contrast,
inverter technology directly controls the power output. This constant
soft penetration of microwave energy prevents the common problems of
shrinkage, overcooking, and loss of nutrients. The result is even food
temperature and textures throughout."

--

Jeff

On 15/05/2021 08:57, Brian Gaff (Sofa) wrote:
There is no such thing as low power on a Magnetron, they simply put it on
and off to simulate the lower energy over time so to speak.

Is the filament reading OK?

Also, I was intrigued by the diode being such a poor conductor in one
direction, in your previous post. However as you have not actually killed
yourself yet, my guess is there is no eht for whatever reason.
Brian

Chris Bacon wrote:
On 15/05/2021 01:02, Paul wrote:
Is it possible the diode is actually made of diodes in series ?

*******

CL01-12 Diode Microwave Oven High Voltage 12kV 350MA

12kV repetitive peak reverse
350mA average output forward
30A surge, 8.3msec, forward
Vf 12V max at 350mA --- about 12 diodes in series or so
at roughly 1V drop on each,
cannot be
checked on "diode" range of
multimeter
2 to 50ua reverse leakage

You would need to make up a little test circuit
to verify the forward characteristic.


No idea. It's a CL04-12 if that makes a difference. I don't know what a
test circuit would be.

To be applied only with the diode out of the circuit.

(+) band
+18V (two 9V battery) -------- R1 ------ diode ----+
|
GND -----------------------------------------------+

Itest = 18V - 12V / R1 = 6 / R1 [Very approximate equation]

R1 = 100K Itest = 60uA
R1 = 10K Itest = 600uA
R1 = 1K Itest = 6mA

V_across_diode + Plotting the diode
| X forward characteristic
|
| X
| X
+-------------------- Itest

Now, reverse the diode so it is reverse biased. No current should
flow. But we know that the diode does have some reverse leakage.
2uA * 100K = 0.2V , Vdiode = 17.8V, 0.2V across R1. The only
effect from changing R1, is to change the drop voltage value.
So across R1, we get the "reverse leakage" while a piddly 18V
is applied. When there is 12kV across the diode, that's when the
real leakage level is realized.

That's an example of building a test circuit, when your meter
is poorly suited to the task. The meter assumes on "diode" range,
that the diode is a single junction, with a 0.7 to 1.0V Vf value.

A TV repairman, spins in his swivel chair, reaches for the Tektronics
curve tracer, throws the diode on it, and traces the diode characteristic
to 100V or so applied voltage. Which would be acceptable for this
task. Curve tracers are good to that sort of test magnitude, somewhere
around 100-150V or so. And likely with fine controls, because if
you were curve tracing one of the mosfets with dual gates, the
ones that are "static sensitive", the gate on those blows out
at 40V, and you'd be very careful to adjust the sweep parameters.

In this little experiment, we're not pushing the diode to avalanche,
as that requires too much test voltage. And would blow out our multimeter :-)
We're manually tracing just a portion of the curve. The nine volt batteries
in the example, can't supply 350mA to "test at rated spec".

http://www.learningaboutelectronics....tics-curve.png

But we can at least see a little bit of "front to back" behavior,
with our higher-voltage power source for test. The meter doesn't
have 18V to apply to our device. I limited my experiment to 6mA,
so the batteries would last.

Paul

Jeff Layman wrote:
Inverter microwave power supplies are effectively continuous at the
power selected. They don't switch on/off in the way that conventional
power supplies do, although they do use pulse-width modulation to
control the power.

This is from http://educypedia.karadimov.info/library/Inverter.pdf
"Inverter Technology In inverter-equipped microwave ovens, the power
transformer is replaced by a circuit board, which converts the 60Hz
incoming line frequency to a variable rate of 20 KHz to 45 KHz. A
relatively small transformer is then required to increase the voltage to
the level required by a magnetron. By varying the pulse width, the
output power can be linearly controlled for more precise cooking and
defrosting levels. The bulky power transformer is replaced by a small,
lightweight circuit board; and, because less heat is dissipated, power
efficiency is increased. Conventional technology uses just a single
power level, which is regulated by switching pulses. In contrast,
inverter technology directly controls the power output. This constant
soft penetration of microwave energy prevents the common problems of
shrinkage, overcooking, and loss of nutrients. The result is even food
temperature and textures throughout."


My inverter microwave, operates PWM from 70% power to 100% power.
It operates in "relay operated ON and OFF" duty cycle, to achieve
levels such as 40% power.

The LG microwave at the store earlier this year, is able to use
PWM below 70%. It represents an improvement on the range the
Panasonic shows.

But at least the earlier inverter based ones, have two operating
modes, PWM for continuous adjustment, then interrupted-mode for
when PWM can't go low enough.

And being an inverter, there's still a diode to rectify the output.
According to this, two diodes, D701 and D702. And the magnetron
filament runs off the inverter transformer.

https://fccid.io/ACLAP4T01/Schematic...atic-77643.pdf

Paul

Chris Bacon wrote:
On 15/05/2021 05:59, jon wrote:

So any help on what's up, and what to do about it?

I had something similar and it turned out to be the magnetron breaking
down under load.

I've got one on order, plus 10 fuses....


The fuses are Slo Blow ? You need to
match the original type, for correct
protection. A regular fuse may blow
too quickly, and blow while the oil-filled
cap is charging up.

Paul

On 15/05/2021 13:42, Paul wrote:
Chris Bacon wrote:
On 15/05/2021 05:59, jon wrote:

So any help on what's up, and what to do about it?

I had something similar and it turned out to be the magnetron breaking
down under load.

I've got one on order, plus 10 fuses....


The fuses are Slo Blow ? You need to
match the original type, for correct
protection. A regular fuse may blow
too quickly, and blow while the oil-filled
cap is charging up.

They match what came out, and are like these ones:

https://www.ebay.co.uk/itm/274464385...AOSw5Yhdacr y

Maybe "extra quick make sure of the job" types?

Jethro_uk wrote:
On Sat, 15 May 2021 09:05:15 +0100, Brian Gaff \(Sofa\) wrote:

But assuming its not some computer controlled device, there is very
little to go wrong, so it might be a simple repair.
Brian

It might be. But as I say 15 years in ????


Also, there aren't many things I am afraid to fiddle with (happily work
on gas, petrol and electricity) but ****ing up a microwave is not a risk
I like to run.

I have some first hand experience with how many
joules are stored in those old microwave oven oil-filled caps.

You don't want to be standing near it, if the HV arcs
over inside the unit. Lost hearing in one ear for
ten minutes.

I'm willing to take the cover off, with its torx security
screws for a "look-see", but touching is out of the question.

And don't be discharging the cap with a screwdriver either.
It's like a gun going off. You want some sort of resistor for
discharging.

http://microwaveovenparts.weebly.com/

"For the high voltage capacitor in a microwave oven, use a
100K ohm resistor rated at least 5 kilovolts and several watts
for your discharge widget, with a clip lead to the chassis.
As a practical matter, a single resistor like this will be hard
to find. So, make one up from a series string of 10 to 20 1/2 W
or 1 W normal resistor.

The reason for specifying the resistor in this way is for
voltage hold-off. Common resistors only are rated for 200 to 500 V,
but there may be as much as 5 kV on the HV cap. You don't want
the HV zapping across the terminals of the resistor. Special
high voltage resistors are available but they are expensive
and not readily available from common electronics distributors".

By that they mean:

--- 10K --- 10K --- 10K --- 10K --- 10K --- 10K ---10K --- 10K --- 10K --- 10K ---

which equals 100K total resistance and 10*resistor_power_rating .
I'd probably aim for a higher value, as that's still likely
to be "noisy enough" if it is energized. The circuit has a
bleeder, but enthusiasts assume the bleeder is open circuit,
before working on such things, and that the capacitor is still
fully armed. The oven itself happens to use 100K ohms, according
to one schematic.

I've worked with higher voltage than that, and where my
resistors were soldered together, I coated with corona dope,
because there was a bit of corona without the coating in place.
You want the resistors soldered, to at least avoid your
contraption "accidentally falling apart while electrified" :-)
Don't just twist the legs on ten resistors like that, when one
croc clip is running at 5kV above ground.

If you're clever, you can probably make Perspex handles for the
"contacts" that touch the capacitor. To avoid getting too close
to the work.

I made a Tesla coil once, but that wasn't nearly as exciting
as Microwave ovens. I could hardly draw any purple sparks out
of mine, and maybe an inch-long discharge was all I got from
the project. Tesla coils are safer, because the high frequency
current travels on the outside of your skin and not through
nerves. The Microwave is DC and your entire body is the
conductor for those purposes.

There's more to know on this topic, and obviously because
Chris is still posting, he knows all this. Me showing
the diagram above, is to at least make you think twice before
sticking a screwdriver shaft across the oil-filled cap terminals.
Using the discharge apparatus is still mondo-dangerous. One
of the reasons I'm still alive today, is keeping a fresh
supply of adrenalin while working. If you're the type that
"gets sleepy" while working on stuff, then just leave the
cover on your microwave.

The microwave discharge that caused me to lose hearing for
ten minutes, that was a flaw in the oven, and *not* me
reaching inside. The conformal coating failed somewhere,
and that's where it arced across. The microwave was one
at work, used to heat microwave popcorn. We learn two things
here. One is, microwave cap is powerful enough, to knock
out your hearing. Two is, microwave popcorn (salt-loaded
clouds of vapor), are a test of the conformal coating,
and too many bags of such popcorn products going
through a microwave, could lead to an "acoustic surprise".

Paul

On 15/05/2021 13:37, Paul wrote:
Jeff Layman wrote:
Inverter microwave power supplies are effectively continuous at the
power selected. They don't switch on/off in the way that conventional
power supplies do, although they do use pulse-width modulation to
control the power.

This is from http://educypedia.karadimov.info/library/Inverter.pdf
"Inverter Technology In inverter-equipped microwave ovens, the power
transformer is replaced by a circuit board, which converts the 60Hz
incoming line frequency to a variable rate of 20 KHz to 45 KHz. A
relatively small transformer is then required to increase the voltage to
the level required by a magnetron. By varying the pulse width, the
output power can be linearly controlled for more precise cooking and
defrosting levels. The bulky power transformer is replaced by a small,
lightweight circuit board; and, because less heat is dissipated, power
efficiency is increased. Conventional technology uses just a single
power level, which is regulated by switching pulses. In contrast,
inverter technology directly controls the power output. This constant
soft penetration of microwave energy prevents the common problems of
shrinkage, overcooking, and loss of nutrients. The result is even food
temperature and textures throughout."


My inverter microwave, operates PWM from 70% power to 100% power.
It operates in "relay operated ON and OFF" duty cycle, to achieve
levels such as 40% power.

The LG microwave at the store earlier this year, is able to use
PWM below 70%. It represents an improvement on the range the
Panasonic shows.

But at least the earlier inverter based ones, have two operating
modes, PWM for continuous adjustment, then interrupted-mode for
when PWM can't go low enough.

And being an inverter, there's still a diode to rectify the output.
According to this, two diodes, D701 and D702. And the magnetron
filament runs off the inverter transformer.

https://fccid.io/ACLAP4T01/Schematic...atic-77643.pdf

The circuitry is also shown in that pdf I linked to. What I find
interesting is that magnetron filament voltage must also vary depending
on the output from the inverter. It obviously isn't critical at all,
and, assuming that at full power its "correct" voltage is being applied,
then at lower powers it must run cooler if the inverter voltage, and so
the output from the transformer filament winding, must be at lower voltage.

--

Jeff

On 15/05/2021 09:41, Chris Bacon wrote:
On 15/05/2021 08:57, Brian Gaff (Sofa) wrote:
There is no such thing as low power on a Magnetron, they simply put it on
and off to simulate the lower energy over time so to speak.
Is the filament reading OK?

Â* Also, I was intrigued by the diode being such a poor conductor in one
direction, in your previous post. However as you have not actually killed
yourself yet, my guess is there is no ehtÂ* for whatever reason.

Why do you think I might kill myself?


Accidentality, not on purpose...

If you can't see Brian's context, then can we get a bit worried for you
and kin?

--
Adrian C

Chris Bacon wrote:
On 15/05/2021 05:59, jon wrote:

So any help on what's up, and what to do about it?

I had something similar and it turned out to be the magnetron breaking
down under load.

I've got one on order, plus 10 fuses....



I didnt realise it was economically viable to replace magnetrons. I must
admit, if our ancient Panasonic ever dies (about 35 years old), if possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�. ;-)

Tim

--
Please don't feed the trolls

On 15/05/2021 18:09, Tim+ wrote:
I didnt realise it was economically viable to replace magnetrons. I must
admit, if our ancient Panasonic ever dies (about 35 years old), if possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�. ;-)

New from China, a fiver. Used in the UK, £6.79. Read the serial number,
internet search. Mine's the ubiquitous Galanz M24FB-610A.

On 15/05/2021 18:09, Tim+ wrote:
Chris Bacon wrote:
On 15/05/2021 05:59, jon wrote:

So any help on what's up, and what to do about it?

I had something similar and it turned out to be the magnetron breaking
down under load.

I've got one on order, plus 10 fuses....

I didnt realise it was economically viable to replace magnetrons. I must
admit, if our ancient Panasonic ever dies (about 35 years old), if possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�. ;-)

I don't think it would be economical to replace the glass turntable on
mine as I think they charge £25 including carriage and the oven cost £40.

In case I break it, I've lifted the turntable from one someone threw out.

--
Max Demian

On 15/05/2021 18:09, Tim+ wrote:
I must
admit, if our ancient Panasonic ever dies (about 35 years old), if possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�.;-)

So does my brand new 'catering' microwave.

And the 45? quid cheapo from Tesco that it replaced


--
€œThose who can make you believe absurdities, can make you commit
atrocities.€�

€• Voltaire, Questions sur les Miracles Ã* M. Claparede, Professeur de
Théologie Ã* Genève, par un Proposant: Ou Extrait de Diverses Lettres de
M. de Voltaire

The Natural Philosopher wrote:
On 15/05/2021 18:09, Tim+ wrote:
I must
admit, if our ancient Panasonic ever dies (about 35 years old), if possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�.;-)

So does my brand new 'catering' microwave.

And the 45? quid cheapo from Tesco that it replaced



But the new timers are horrible (IMO). Our old one allows you to quickly
set minutes and seconds.

(Ours is a Toshiba, not a Panasonic as I originally said). Its the only
microwave weve ever owned.

https://yams.secondhandapp.at/api/v1...e=w1200q75jpeg
(stock picture, not ours).

Tim

--
Please don't feed the trolls

On 15/05/2021 22:26, Max Demian wrote:
On 15/05/2021 18:09, Tim+ wrote:
Chris Bacon wrote:
On 15/05/2021 05:59, jon wrote:

So any help on what's up, and what to do about it?

I had something similar and it turned out to be the magnetron breaking
down under load.

I've got one on order, plus 10 fuses....

I didnt realise it was economically viable to replace magnetrons. I must
admit, if our ancient Panasonic ever dies (about 35 years old), if possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�. ;-)

I don't think it would be economical to replace the glass turntable on
mine as I think they charge £25 including carriage and the oven cost £40.

In case I break it, I've lifted the turntable from one someone threw out.

Why is the turntable made from glass, and not the same metal as the rest
of the microwave oven? Glass is pretty transparent to microwave
frequencies, and the turntable is only a cm or so above the metal floor,
so why not make the turntable from the same metal?

--

Jeff

On 16/05/2021 08:21, Jeff Layman wrote:
Why is the turntable made from glass, and not the same metal as the rest
of the microwave oven? Glass is pretty transparent to microwave
frequencies, and the turntable is only a cm or so above the metal floor,
so why not make the turntable from the same metal?

Yes, that. Mine's a steel one. There's a resistive heating element
under, which allows the turntable to be used to make nice pizzas in!

On 16/05/2021 07:35, Tim+ wrote:
The Natural Philosopher wrote:
On 15/05/2021 18:09, Tim+ wrote:
I must
admit, if our ancient Panasonic ever dies (about 35 years old), if possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�.;-)

So does my brand new 'catering' microwave.

And the 45? quid cheapo from Tesco that it replaced



But the new timers are horrible (IMO). Our old one allows you to quickly
set minutes and seconds.

so does mine, to about 10 second accuracy - who needs more?


https://www.caterkwik.co.uk/cgi-bin/...showprod_GK643


(Ours is a Toshiba, not a Panasonic as I originally said). Its the only
microwave weve ever owned.

https://yams.secondhandapp.at/api/v1...e=w1200q75jpeg
(stock picture, not ours).

Tim



--
When plunder becomes a way of life for a group of men in a society, over
the course of time they create for themselves a legal system that
authorizes it and a moral code that glorifies it.

Frédéric Bastiat

On 15/05/2021 23:29, The Natural Philosopher wrote:
On 15/05/2021 18:09, Tim+ wrote:
I must
admit, if our ancient Panasonic ever dies (about 35 years old), if
possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�.;-)

So does my brand new 'catering' microwave.

And the 45? quid cheapo from Tesco that it replaced


While I am all for repair in general, IMHO the functionality of
"expensive" microwaves (oven, grill, etc) is a waste of time. I think I
replaced a fuse in one once, but they are a minefield even for
experienced repairers unless you actually have a background in them. So
I with TNP here, throw it away and replace with a £50 or less basic. It
will go in the "metals" skip at the tip so the steel, stainless steel,
and copper will all get recovered and recycled. I don't believe there
will be enough on the PCB to be worth recovering, but perhaps as robots
get smarter they will get plucked out before shredding too.

On 16/05/2021 08:21, Jeff Layman wrote:
On 15/05/2021 22:26, Max Demian wrote:

I don't think it would be economical to replace the glass turntable on
mine as I think they charge £25 including carriage and the oven cost £40.

In case I break it, I've lifted the turntable from one someone threw out.

Why is the turntable made from glass, and not the same metal as the rest
of the microwave oven? Glass is pretty transparent to microwave
frequencies, and the turntable is only a cm or so above the metal floor,
so why not make the turntable from the same metal?

I suppose it's for ease of cleaning, but they could coat it with Teflon.

There must be a reason - maybe that it usually is just above the floor
on a "spider", so a metal turntable would heat up unless recessed in the
floor.

--
Max Demian

On 16/05/2021 11:40, Max Demian wrote:
On 16/05/2021 08:21, Jeff Layman wrote:
On 15/05/2021 22:26, Max Demian wrote:

I don't think it would be economical to replace the glass turntable on
mine as I think they charge £25 including carriage and the oven cost
£40.

In case I break it, I've lifted the turntable from one someone threw
out.

Why is the turntable made from glass, and not the same metal as the
rest of the microwave oven? Glass is pretty transparent to microwave
frequencies, and the turntable is only a cm or so above the metal
floor, so why not make the turntable from the same metal?

I suppose it's for ease of cleaning, but they could coat it with Teflon.

There must be a reason - maybe that it usually is just above the floor
on a "spider", so a metal turntable would heat up unless recessed in the
floor.

I don't think that is the issue. I think the issue is not to shield the
underside of the food from reflected microwaves.

--
When plunder becomes a way of life for a group of men in a society, over
the course of time they create for themselves a legal system that
authorizes it and a moral code that glorifies it.

Frédéric Bastiat

On 16/05/2021 08:21, Jeff Layman wrote:
On 15/05/2021 22:26, Max Demian wrote:
On 15/05/2021 18:09, Tim+ wrote:
Chris Bacon wrote:
On 15/05/2021 05:59, jon wrote:

So any help on what's up, and what to do about it?

I had something similar and it turned out to be the magnetron breaking
down under load.

I've got one on order, plus 10 fuses....

I didnt realise it was economically viable to replace magnetrons.Â* I
must
admit, if our ancient Panasonic ever dies (about 35 years old), if
possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�. ;-)

I don't think it would be economical to replace the glass turntable on
mine as I think they charge £25 including carriage and the oven cost £40.

In case I break it, I've lifted the turntable from one someone threw out.

Why is the turntable made from glass, and not the same metal as the rest
of the microwave oven? Glass is pretty transparent to microwave
frequencies, and the turntable is only a cm or so above the metal floor,
so why not make the turntable from the same metal?

At a metallic boundary there will zero electric field, I guess lifting
the food to be warmed away from the metallic bottom into the microwave
field will help to ensure the food doesn't get a cold spot.

On 16/05/2021 07:35, Tim+ wrote:
The Natural Philosopher wrote:
On 15/05/2021 18:09, Tim+ wrote:
I must
admit, if our ancient Panasonic ever dies (about 35 years old), if possible
I would like it repaired as it has a €œproper€� mechanical countdown timer
and a real bell that goes €œding€�.;-)

So does my brand new 'catering' microwave.

And the 45? quid cheapo from Tesco that it replaced



But the new timers are horrible (IMO). Our old one allows you to quickly
set minutes and seconds.

(Ours is a Toshiba, not a Panasonic as I originally said). Its the only
microwave weve ever owned.

https://yams.secondhandapp.at/api/v1...e=w1200q75jpeg
(stock picture, not ours).

I have one like that still going.

How do Panasonic inverter microwaves work then ?.

My trusty, reliable Sharp just pulsed on and off in varying times
when a power setting less than 100% was chosen, but the Panny sounds
the same om Medium as it does on full power.

Andrew

On 15/05/2021 08:57, Brian Gaff (Sofa) wrote:
There is no such thing as low power on a Magnetron, they simply put it on
and off to simulate the lower energy over time so to speak.

Is the filament reading OK?

Also, I was intrigued by the diode being such a poor conductor in one
direction, in your previous post. However as you have not actually killed
yourself yet, my guess is there is no eht for whatever reason.
Brian