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OT magnetron service life



 
 
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  #21  
Old December 3rd 13, 12:43 AM posted to uk.tech.digital-tv
Johny B Good[_2_]
external usenet poster
 
Posts: 853
Default OT magnetron service life

On Mon, 02 Dec 2013 22:53:41 +0000, lid wrote:

On Sun, 01 Dec 2013 18:59:20 +0000, Johny B Good
wrote:

Haven't read the thread but this may be of interest..

http://www.dailymail.co.uk/news/arti...--Spencer.html

Interesting, it looks like he died from a good old fashioned electric
shock from mains voltage rather the -4.5KV EHT to the magnetron
cathode/heater connections if the description "an uninsulated
controller to a magnetron" has _any_ basis in fact. To me, the word
'controller' in this context means a relay operated switch carrying
mains voltage to the 2KV step up transformer or inverter used to power
the magnetron and its cathode heater circuit.

Since they weren't able to resuscitate him, I think it more likely to
be inaccurate reporting of the fact that he was electrocuted by the
EHT supply. It's this phrase in the article "finding him dead on the
floor" after immediately coming to his aid that worries me.

You'd think a large store would have an emergency defibrillator to
hand or else, failing that particular luxury (item), at least one
person capable of applying CPR until the paramedics arrive on the
scene.

Being rather leery of anything that's mains powered, let alone one
with a -4.5KV EHT supply capable of supplying nearly half an amp, I
stand well clear when operating the front panel user controls (and
make damn sure the thing is unplugged from the mains at all other
times whilst the cover is removed).

Even when the oven is unplugged from the mains, the EHT capacitor can
still retain a considerable charge if there's no built in bleed
resistor or said resistor has failed open circuit. There could still
be 1 to 2 KV lurking about on a capacitor measured in microFarads
rather than the few hundred picoFarads of that Leyden Jar affair that
those in the TV trade would more usually describe as the picture tube
(or valve).

A shock from the stored charge on a colour picture tube is but a
playful tickle compared to that which awaits the unwary would be
microwave oven 'tinkerer'. Even testing for the presence of stored
charge on that capacitor after unplugging from the mains supply is
problematical. For a start you need meter probes rated to at least 3KV
(there could be as much as 2.8KV due to heater failure of the
magnetron and an open circuit (or absence of) safety bleeder resistor.

Even so, you would be well advised to clip the positive test lead to
chassis ground before, single handedly, applying the negative test
probe to the heater/cathode terminals. I have to admit, this was one
test I didn't feel the need to make. I feel that life's short enough
already as it is with all the 'regular' risks in the environment that
threaten life and limb.
--
Regards, J B Good
  #22  
Old December 3rd 13, 11:17 AM posted to uk.tech.digital-tv
external usenet poster
 
Posts: 1,236
Default OT magnetron service life

On Tue, 03 Dec 2013 01:43:39 +0000, Johny B Good
wrote:

On Mon, 02 Dec 2013 22:53:41 +0000, lid wrote:

On Sun, 01 Dec 2013 18:59:20 +0000, Johny B Good
wrote:

Haven't read the thread but this may be of interest..

http://www.dailymail.co.uk/news/arti...--Spencer.html

Interesting, it looks like he died from a good old fashioned electric
shock from mains voltage rather the -4.5KV EHT to the magnetron
cathode/heater connections if the description "an uninsulated
controller to a magnetron" has _any_ basis in fact. To me, the word
'controller' in this context means a relay operated switch carrying
mains voltage to the 2KV step up transformer or inverter used to power
the magnetron and its cathode heater circuit.

Since they weren't able to resuscitate him, I think it more likely to
be inaccurate reporting of the fact that he was electrocuted by the
EHT supply. It's this phrase in the article "finding him dead on the
floor" after immediately coming to his aid that worries me.

You'd think a large store would have an emergency defibrillator to
hand or else, failing that particular luxury (item), at least one
person capable of applying CPR until the paramedics arrive on the
scene.

Being rather leery of anything that's mains powered, let alone one
with a -4.5KV EHT supply capable of supplying nearly half an amp, I
stand well clear when operating the front panel user controls (and
make damn sure the thing is unplugged from the mains at all other
times whilst the cover is removed).

Even when the oven is unplugged from the mains, the EHT capacitor can
still retain a considerable charge if there's no built in bleed
resistor or said resistor has failed open circuit. There could still
be 1 to 2 KV lurking about on a capacitor measured in microFarads
rather than the few hundred picoFarads of that Leyden Jar affair that
those in the TV trade would more usually describe as the picture tube
(or valve).

A shock from the stored charge on a colour picture tube is but a
playful tickle compared to that which awaits the unwary would be
microwave oven 'tinkerer'. Even testing for the presence of stored
charge on that capacitor after unplugging from the mains supply is
problematical. For a start you need meter probes rated to at least 3KV
(there could be as much as 2.8KV due to heater failure of the
magnetron and an open circuit (or absence of) safety bleeder resistor.

Even so, you would be well advised to clip the positive test lead to
chassis ground before, single handedly, applying the negative test
probe to the heater/cathode terminals. I have to admit, this was one
test I didn't feel the need to make. I feel that life's short enough
already as it is with all the 'regular' risks in the environment that
threaten life and limb.


I can't understand why he was called in to repair a microwave oven.
Even the minimum callout charge would probably have paid for a
replacement oven. Much quicker, easier and cheaper to pop next door to
Argos/Currys/whatever for a new one.
  #23  
Old December 3rd 13, 12:47 PM posted to uk.tech.digital-tv
Peter Duncanson
external usenet poster
 
Posts: 4,182
Default OT magnetron service life

On Tue, 03 Dec 2013 12:17:13 +0000, lid wrote:

On Tue, 03 Dec 2013 01:43:39 +0000, Johny B Good
wrote:

On Mon, 02 Dec 2013 22:53:41 +0000,
lid wrote:

On Sun, 01 Dec 2013 18:59:20 +0000, Johny B Good
wrote:

Haven't read the thread but this may be of interest..

http://www.dailymail.co.uk/news/arti...--Spencer.html

Interesting, it looks like he died from a good old fashioned electric
shock from mains voltage rather the -4.5KV EHT to the magnetron
cathode/heater connections if the description "an uninsulated
controller to a magnetron" has _any_ basis in fact. To me, the word
'controller' in this context means a relay operated switch carrying
mains voltage to the 2KV step up transformer or inverter used to power
the magnetron and its cathode heater circuit.

Since they weren't able to resuscitate him, I think it more likely to
be inaccurate reporting of the fact that he was electrocuted by the
EHT supply. It's this phrase in the article "finding him dead on the
floor" after immediately coming to his aid that worries me.

You'd think a large store would have an emergency defibrillator to
hand or else, failing that particular luxury (item), at least one
person capable of applying CPR until the paramedics arrive on the
scene.

Being rather leery of anything that's mains powered, let alone one
with a -4.5KV EHT supply capable of supplying nearly half an amp, I
stand well clear when operating the front panel user controls (and
make damn sure the thing is unplugged from the mains at all other
times whilst the cover is removed).

Even when the oven is unplugged from the mains, the EHT capacitor can
still retain a considerable charge if there's no built in bleed
resistor or said resistor has failed open circuit. There could still
be 1 to 2 KV lurking about on a capacitor measured in microFarads
rather than the few hundred picoFarads of that Leyden Jar affair that
those in the TV trade would more usually describe as the picture tube
(or valve).

A shock from the stored charge on a colour picture tube is but a
playful tickle compared to that which awaits the unwary would be
microwave oven 'tinkerer'. Even testing for the presence of stored
charge on that capacitor after unplugging from the mains supply is
problematical. For a start you need meter probes rated to at least 3KV
(there could be as much as 2.8KV due to heater failure of the
magnetron and an open circuit (or absence of) safety bleeder resistor.

Even so, you would be well advised to clip the positive test lead to
chassis ground before, single handedly, applying the negative test
probe to the heater/cathode terminals. I have to admit, this was one
test I didn't feel the need to make. I feel that life's short enough
already as it is with all the 'regular' risks in the environment that
threaten life and limb.


I can't understand why he was called in to repair a microwave oven.
Even the minimum callout charge would probably have paid for a
replacement oven. Much quicker, easier and cheaper to pop next door to
Argos/Currys/whatever for a new one.


The electrician worked for Millers Vanguard. Millers Vanguard has
contractual arrangements with its customers. Presumably M&S had a
contract with that company to do electrical work in that and other
stores. In that case the electrician would be the equivalent of an
in-house electrician. If an electrical appliance is faulty he would
investigate and decide whether a simple repair is possible or whether it
should be replaced.

In that sort of environment it can be important to have a qualified
person decide whether an appliance is faulty or not. There is always the
possibility of some junior manager dishonestly declaring an appliance to
be faulty, arranging a replacement and then helpfully removing the
"faulty" item which is then sold on or used happily for years in that
person's home.

Millers Vanguard Reactive Maintenance:
http://www.millersvanguard.co.uk/reactive-maintenance/

Contacting our 24/7 state-of-the-art National Service Response
Centre your call will be put through to a qualified Engineer who
will screen the call, enabling us to contact you directly for a
remote fix wherever possible.

If a remote fix cannot be achieved we will send out an Engineer
within your contractual Service Level Agreement from a 4-hour
response onwards. All our vans are constantly tracked in order that
we can select the closest engineer for the fastest service. What’s
more, if our Engineer’s call screening has identified a requirement
for parts that are not carried in our Field Engineers’ extensive van
stock these are dispatched for delivery before 8am the next day.

All Reactive Engineers carry a PDA unit which not only sends them
precise details of each job but also gives them instant access to
our vast technical library helping them to achieve an 85%+ first
time fix rate. Where a device cannot be fixed on site it can be
rapidly replaced with a ready-to-dispatch loan device from our
extensive warehouse asset stock.


--
Peter Duncanson
(in uk.tech.digital-tv)
  #24  
Old January 1st 15, 03:04 AM posted to uk.tech.digital-tv
external usenet poster
 
Posts: 1
Default OT magnetron service life

I have a Toshiba ER-672 with a mechanical timer and a bell. Yes, it goes 'ding' and just once too. I've had it for 30 years and 7 months and in that time I've only had one failure, the globe. That was until yesterday when it started making a loud buzzing noise. Time to retire it and get a new one I thought. That was until I read copious on-line reviews complaining about the extremely poor quality and reliability of modern microwave ovens. I visited all 5 electrical stores in my area and looked at all available ovens which only supported the complaints I'd read on-line. Decided to see if I could resurrect my old Toshiba so I opened the cover and found that the high voltage diode was shorted. A new one is on order, they cost just $5 so I'm hopeful that will keep it going for a few more decades. Once it's working again I'll measure its heating capacity but I have no reason to think it is less than the 650w it was when new.
  #26  
Old January 1st 15, 08:04 AM posted to uk.tech.digital-tv
Tim+[_2_]
external usenet poster
 
Posts: 83
Default OT magnetron service life

wrote:
I have a Toshiba ER-672 with a mechanical timer and a bell. Yes, it goes
'ding' and just once too. I've had it for 30 years and 7 months and in
that time I've only had one failure, the globe. That was until yesterday
when it started making a loud buzzing noise. Time to retire it and get a
new one I thought. That was until I read copious on-line reviews
complaining about the extremely poor quality and reliability of modern
microwave ovens. I visited all 5 electrical stores in my area and looked
at all available ovens which only supported the complaints I'd read
on-line. Decided to see if I could resurrect my old Toshiba so I opened
the cover and found that the high voltage diode was shorted. A new one is
on order, they cost just $5 so I'm hopeful that will keep it going for a
few more decades. Once it's working again I'll measure its heating
capacity but I have no reason to think it is less than the 650w it was when new.



Our old Toshiba from the early 80s is still going strong.

Tim
  #28  
Old January 1st 15, 11:41 AM posted to uk.tech.digital-tv
Brian Gaff[_2_]
external usenet poster
 
Posts: 1,003
Default OT magnetron service life

Well, I've never had one go. Modern machines cut the power if the standing
waves get back to the Magnetron to protect the things guts.


Of course yours may not be that sophisticated.
The Microwaves generally though do seem to make a loud buzz assumedly this
is the transformer rattling at 50 hz. Nobody has made a switch mode supply
big enough and safe enough I'd suspect.
Brian

--
From the Sofa of Brian Gaff Reply address is active
wrote in message
...
I have a Toshiba ER-672 with a mechanical timer and a bell. Yes, it goes
'ding' and just once too. I've had it for 30 years and 7 months and in that
time I've only had one failure, the globe. That was until yesterday when it
started making a loud buzzing noise. Time to retire it and get a new one I
thought. That was until I read copious on-line reviews complaining about the
extremely poor quality and reliability of modern microwave ovens. I visited
all 5 electrical stores in my area and looked at all available ovens which
only supported the complaints I'd read on-line. Decided to see if I could
resurrect my old Toshiba so I opened the cover and found that the high
voltage diode was shorted. A new one is on order, they cost just $5 so I'm
hopeful that will keep it going for a few more decades. Once it's working
again I'll measure its heating capacity but I have no reason to think it is
less than the 650w it was when new.


  #29  
Old January 1st 15, 11:44 AM posted to uk.tech.digital-tv
Brian Gaff[_2_]
external usenet poster
 
Posts: 1,003
Default OT magnetron service life

The Philips one I had only died due to the door going rusty, it had a bottom
hinge, and fell off!

Brian

--
From the Sofa of Brian Gaff Reply address is active
"NY" wrote in message
...
"Indy Jess John" wrote in message
...
On 01/01/2015 04:04, wrote:
I have a Toshiba ER-672 with a mechanical timer and a bell. Yes, it goes
'ding' and just once too. I've had it for 30 years and 7 months and in
that time I've only had one failure, the globe. That was until yesterday
when it started making a loud buzzing noise. Time to retire it and get a
new one I thought. That was until I read copious on-line reviews
complaining about the extremely poor quality and reliability of modern
microwave ovens.


My Mum bought one of the early Panasonic microwaves, also with mechanical
timer. She used it at least once every day.

It never went wrong. When she died, my sister gave it to a charity shop.

I don't think it was 30 years old, but it was certainly more than 20. And
you are right about the modern ones not lasting so long. I am using the
third I have bought since my Mum bought hers.


My mum's microwave (mechanical timer, bell - not sure what make) is still
going strong and it's at least 35 years old. I know this because she got
it while my grandpa was still alive (he died in 1978) and we had to be
careful not to operate it when he was nearby because he had a heart
pacemaker.



  #30  
Old January 1st 15, 12:29 PM posted to uk.tech.digital-tv
Paul Ratcliffe
external usenet poster
 
Posts: 2,410
Default OT magnetron service life

On Thu, 01 Jan 2015 08:44:28 +0000, Indy Jess John
wrote:

I have a Toshiba ER-672 with a mechanical timer and a bell. Yes, it goes 'ding' and just once too. I've had it for 30 years and 7 months and in that time I've only had one failure, the globe. That was until yesterday when it started making a loud buzzing noise. Time to retire it and get a new one I thought. That was until I read copious on-line reviews complaining about the extremely poor quality and reliability of modern microwave ovens.


My Mum bought one of the early Panasonic microwaves, also with
mechanical timer. She used it at least once every day.

It never went wrong. When she died, my sister gave it to a charity shop.

I don't think it was 30 years old, but it was certainly more than 20.
And you are right about the modern ones not lasting so long. I am using
the third I have bought since my Mum bought hers.


My mother's is about 30 and mine is 23. Both Panasonic. Both work well.

Dunno what the relevance to digital TV is though.
 




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