Feedback welcome...



Appliance repair hazards


The main hazards in appliance repairs are summarized. There are always
others that have the potential to occur too.


==Common risks==
Some risks are common to all mains appliances:
* shock if plugged in
* basic wiring faults

==Microwave==
These are one of the highest risk domestic appliances to repair. The
EHT supply in particular tends to be fatal if touched, and has killed
experienced technicians.
* EHT supply for magnetron
* Parts connected to EHT supply: LT magnetron supply wires,
transformer, capacitor, rectifier
* Power supply capacitors sometimes store thousands of volts even when
unplugged
* Misalignment or miswiring of interlock switches
* Failed shorting resistor when replacing [[fuse]]
* Microwave leakage after replacing a component
* Microwave leakage from rust holing
* Sharp edges

===Old microwaves===
Old machines from the beginning of the '80s and before can have:
* unsafe interlock system.
* carbon loaded rubber seals prone to coming adrift, permitting
leakage

Some 1970s and earlier machines have power controls that switch the
EHT directly, making all internal parts of the power control and
associated wiring dangerous to touch until the EHT has been fully
discharged.

Commercial machines from the 1960s and before are uncommon, but do
exist, and in a minority of cases can continue cooking with the door
part way open. These are hopelessly unsafe.

===Damaged microwaves===
The mains risks a
* missing or damaged door grille cooks the user
* warped door
* missing seals on old machines
* damaged door hinges
* door misalignment


==TV==
===CRT TV===
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* EHT supply, stored by the picture tube when off
* Focus voltage, also stored
* Propped appliance can fall on child or pet
* Picture tube may explode if the unprotected thin rear of the tube is
broken

===LCD TV===
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* High voltage stored in lighting invertor
* Weak thin glass: screen and backlight

===Antique TV===
Just a note that very old TVs are somewhat different to modern kit,
especially in picture tube safety. Old picture tubes from the 1970s
and earlier may lack a rimband, resulting in explosion if the tube's
reinforced front glass is broken. Older pre-1960 picture tubes that
use a separate plate glass shield to protect them are both fragile and
explosive, and require treating with respect.

The EHT supplies in historic TVs can bite, but are normally safer than
modern sets, and pose little risk to life. The exception is rare pre-
war sets, which often contain a dangerous type of EHT supply.


==Washing machine==
* Mains filter sometimes stores mains voltage after the machine's
unplugged.
* Power supply for controller stores mains voltage when unplugged
* Hand can get caught in mechanical parts
* Ill fitting spanners can slip, causing minor injury


==See Also==
* [[Special:Allpages|Wiki Contents]]
* [[Special:Categories|Wiki Subject Categories]]



[[Category:Appliances]]
[[Category:Electrical]]
[[Category:Fault Finding]]
[[Category:Repair]]
[[Category:Safety]]
[[Category:TV]]

wrote:
Feedback welcome...



Appliance repair hazards


The main hazards in appliance repairs are summarized. There are always
others that have the potential to occur too.


==Common risks==
Some risks are common to all mains appliances:
* shock if plugged in
* basic wiring faults

==Microwave==
These are one of the highest risk domestic appliances to repair. The
EHT supply in particular tends to be fatal if touched, and has killed
experienced technicians.
* EHT supply for magnetron
* Parts connected to EHT supply: LT magnetron supply wires,
transformer, capacitor, rectifier
* Power supply capacitors sometimes store thousands of volts even when
unplugged
* Misalignment or miswiring of interlock switches
* Failed shorting resistor when replacing [[fuse]]
* Microwave leakage after replacing a component
* Microwave leakage from rust holing
* Sharp edges

===Old microwaves===
Old machines from the beginning of the '80s and before can have:
* unsafe interlock system.
* carbon loaded rubber seals prone to coming adrift, permitting
leakage

Some 1970s and earlier machines have power controls that switch the
EHT directly, making all internal parts of the power control and
associated wiring dangerous to touch until the EHT has been fully
discharged.

Commercial machines from the 1960s and before are uncommon, but do
exist, and in a minority of cases can continue cooking with the door
part way open. These are hopelessly unsafe.

===Damaged microwaves===
The mains risks a
* missing or damaged door grille cooks the user
* warped door
* missing seals on old machines
* damaged door hinges
* door misalignment


==TV==
===CRT TV===
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* EHT supply, stored by the picture tube when off
* Focus voltage, also stored
* Propped appliance can fall on child or pet
* Picture tube may explode if the unprotected thin rear of the tube is
broken

===LCD TV===
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* High voltage stored in lighting invertor
* Weak thin glass: screen and backlight

===Antique TV===
Just a note that very old TVs are somewhat different to modern kit,
especially in picture tube safety. Old picture tubes from the 1970s
and earlier may lack a rimband, resulting in explosion if the tube's
reinforced front glass is broken. Older pre-1960 picture tubes that
use a separate plate glass shield to protect them are both fragile and
explosive, and require treating with respect.

The EHT supplies in historic TVs can bite, but are normally safer than
modern sets, and pose little risk to life. The exception is rare pre-
war sets, which often contain a dangerous type of EHT supply.


==Washing machine==
* Mains filter sometimes stores mains voltage after the machine's
unplugged.

I read 'filter' as being a water type filter on the incoming waters 'mains'.
I guess you are using it to mean something electrical?

* Power supply for controller stores mains voltage when unplugged
* Hand can get caught in mechanical parts
* Ill fitting spanners can slip, causing minor injury

I've cut myself a couple of times on the sharp edges of the thin sheet metal
used to make the backs.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

Don't think that dropping 'EHT' in there is very helpful. I suspect
many/most people reading would not know what that is - I am guessing
extra high tension?

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

===CRT TV===
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* EHT supply, stored by the picture tube when off
* Focus voltage, also stored
* Propped appliance can fall on child or pet
* Picture tube may explode if the unprotected thin rear of the tube is
broken

We used to dispose of lots of 'gassy' tubes by tapping the thin rear
nipple on the tube with a long screwdriver. Never had one explode. The
cautious among us used to cover it with bubble wrap - which used to
get sucked inside!

wrote:
Feedback welcome...
.... snipped


==TV==
===CRT TV===
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* EHT supply, stored by the picture tube when off
* Focus voltage, also stored
* Propped appliance can fall on child or pet
* Picture tube may explode if the unprotected thin rear of the tube is
broken
.... snipped

All good but a couple of niggles:
- CRTs implode, not explode
- "Propped appliance can fall on child or pet" is not unique to a TV and
is OTT. Better to say that they are surprisingly heavy and that the
weight is concentrated towards the front (avoiding terms like CofG)
- May want to discuss degassing by crushing the nipple - but then you
need to explain about covering the CRT in case of implosion

Dave

==TV==
===CRT TV===
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* EHT supply, stored by the picture tube when off
* Focus voltage, also stored
* Propped appliance can fall on child or pet
* Picture tube may explode if the unprotected thin rear of the tube is
broken



I thought CRT TVs imploded.


mark

"Phil" wrote in message
...

===CRT TV===
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* EHT supply, stored by the picture tube when off
* Focus voltage, also stored
* Propped appliance can fall on child or pet
* Picture tube may explode if the unprotected thin rear of the tube is
broken

We used to dispose of lots of 'gassy' tubes by tapping the thin rear
nipple on the tube with a long screwdriver. Never had one explode. The
cautious among us used to cover it with bubble wrap - which used to
get sucked inside!

Back in the day, our local tip didn't sort anything - all was chucked from a
height down onto concrete and every now and then a digger came and cleared
the area. We used to take great delight in disposing of CRT tubes by hurling
them onto the concrete so they did explode. Happy days....


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

In article ,
Rod writes:
Don't think that dropping 'EHT' in there is very helpful. I suspect
many/most people reading would not know what that is - I am guessing
extra high tension?

Not to be confused with hyper tension, which results from the
damn thing busting in the first place...

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Feedback welcome...


The most serious omission IMHO is there is no reference to
the hazards encountered when servicing, or connecting peripheral
devices or test equipment to "live chassis" radio and televisions.
These was mainly valve or hybrid (valve & semiconductor)
sets, but some "all transistor" sets were also live chassis.

The chassis is supposed to be connected to the supply neutral, but
even if you check the polarity it would be very unwise to work
on it without an isolating transformer.

After about the mid 70's a different kind of live chassis is
encountered. This time the chassis is connected to the -ve
of the mains bridge rectifier. Consequently, the chassis is
*always* at half mains potential irrespective of plug polarity

With both these variants of live chassis, use an isolating transformer
rated for the full continuous load (not an insubstantial piece of kit)
whilst the back is off, and ideally, when in normal operation too.

Finally, the aerial socket will be isolated with built-in capacitors,
ensure this hasn't been tampered with. Imagine getting a serious shock
whilst in the roof!



--
Graham.

%Profound_observation%

wrote:
Feedback welcome...

Thanks for the suggestions. version 2....


The main hazards in appliance repairs are summarized. There are always
others that have the potential to occur too.


==Common risks==
Some risks are common to all mains appliances:
* Shock if plugged in
* Basic wiring faults


==Microwave==
These are one of the highest risk domestic appliances to repair. The
EHT supply in particular tends to be fatal if touched, and has killed
experienced technicians. (EHT = very high voltage.)
* EHT supply for magnetron
* Parts connected to EHT supply: LT magnetron supply wires,
transformer, capacitor, rectifier
* Power supply capacitors sometimes store thousands of volts even when
unplugged
* Misalignment or miswiring of interlock switches
* Failed shorting resistor when replacing [[fuse]]
* Microwave leakage after replacing a component
* Microwave leakage from rust holing
* Sharp edges

===Old microwaves===
Old machines from the beginning of the '80s and before can have:
* unsafe interlock system.
* carbon loaded rubber seals prone to coming adrift, permitting
leakage

Some 1970s and earlier machines have power controls that switch the
EHT directly, making all internal parts of the power control and
associated wiring dangerous to touch until the EHT has been fully
discharged.

Commercial machines from the 1960s and before are uncommon, but do
exist, and in a minority of cases can continue cooking with the door
part way open. These are hopelessly unsafe.

===Damaged microwaves===
The mains risks a
* missing or damaged door grille cooks the user
* warped door
* missing seals on old machines
* damaged door hinges
* door misalignment


==TV==
===CRT TV===
TVs with bulky picture tubes are the other domestic appliance with
assorted internal safety issues.
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* EHT supply, stored by the picture tube when off
* Focus voltage, also stored
* HT supply, again often stored
* Propped appliance can fall on child or pet. CRT sets have their
centre of gravity far forward, and often surprise casual repairers by
toppling unexpectedly.
* Live chassis were common until the 1980s. Connecting external
devices to these sets can shock, or in the case of headphones can
kill. (Note that a minority of live chassis sets have headphone
outputs driven by small isolating transformers, so existence of such a
socket does not imply it has an isolated chassis.)
* Picture tube may explode if the unprotected thin rear of the tube is
broken. (Breaking the nipple is the standard disposal method.) The
large vacuum in the tube causes implosion, and the broken glass can
bounce back out explosively.


===LCD TV===
Flat panel sets have much less internal safety issues.
* Power supply capacitors store hundreds of volts even when unplugged.
This voltage is distributed around some parts of the circuit board.
* High voltage stored in lighting invertor
* Weak thin glass: screen and backlight

===Antique TV===
Just a note that very old TVs are somewhat different to modern kit,
especially in picture tube safety. Old picture tubes from the 1970s
and earlier may lack a rimband, resulting in a good chance of
explosion if the tube's reinforced front glass is broken. Older
pre-1960 picture tubes that use a separate plate glass shield to
protect them are both fragile and explosive, and require treating with
respect.

The EHT supplies in historic black & white TVs can bite, but are
normally safer than modern sets, and pose little risk to life. The
exception is rare pre-war sets, which usually contain a dangerous type
of EHT supply.


==Washing machine==
* Mains filter sometimes stores mains voltage after the machine's
unplugged.
* Power supply for controller stores mains voltage when unplugged
* Hand can get caught in mechanical parts
* Ill fitting spanners can slip, causing minor injury
* Sharp metal edges sometimes found on internal sheet metal


==Radio==
* Presence of mains in the cabinet
===Historic radio===
* Some pre-1970 valve radios known as universal sets used a live
chassis arrangement. Connecting external devices to these is
dangerous.
* Old valve radios may retain 100s of volts of charge in the reservoir
capacitors when unplugged.
* Curtain burner sets are rare, the mains lead on these gets hot in
use, with predictable results if not well ventilated along its full
length.



==See Also==
* [[Special:Allpages|Wiki Contents]]
* [[Special:Categories|Wiki Subject Categories]]



[[Category:Appliances]]
[[Category:Electrical]]
[[Category:Fault Finding]]
[[Category:Repair]]
[[Category:Safety]]
[[Category:TV]]

In article ,
"mark" writes:

I thought CRT TVs imploded.

That just means the pieces shooting out in your direction came
from the opposite side originally.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

NoSpam wrote:
wrote:
Feedback welcome...
... snipped

snipped some more

- "Propped appliance can fall on child or pet" is not unique to a TV
and is OTT.

Likewise "ill fitting spanners" is not the fault of the washing machine.
(Unless they come with them?)

on 09/12/2008, supposed :
* Picture tube may explode if the unprotected thin rear of the tube is
broken

They are under vacuum and therefore implode though the result can be
the same anyway.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

* Picture tube may explode if the unprotected thin rear of the tube is
broken. (Breaking the nipple is the standard disposal method.) The
large vacuum in the tube causes implosion, and the broken glass can
bounce back out explosively.


I'm not at all happy with the idea that breaking the area near the
EHT connector is safe, in fact IMHO I can't think of a more
dangerous way to destroy a tube.

The standard way of destroying the vacuum is to crack the *neck*
with a small hammer ot the handle or a long screwdriver.
It is easy to do because the glass is thin at this point, and the
narrow neck ensures that the air rushes in comparatively
slowly with a hiss rather than Earth-shattering KABOOM
--
Graham.

%Profound_observation%

"PM" wrote in message
...
NoSpam wrote:
wrote:
Feedback welcome...
... snipped

snipped some more

- "Propped appliance can fall on child or pet" is not unique to a TV
and is OTT.

Likewise "ill fitting spanners" is not the fault of the washing machine.
(Unless they come with them?)

I strongly disagree with you, this is a wiki for the in-initiated, and both
warnings should remain.
Many modern CRT sets become very unstable if you attempt to remove
the back cover with the set on its stand. The weight of the tube makes
the whole escutcheon rake forward, along with the centre of mass.

As for the other point about ill-fitting tools in white goods, I would be
in favour of removing the word "minor" in "minor injuries" as slashed
wrists have been known to be fatal!

--
Graham.

%Profound_observation%

this is a wiki for the in-initiated,
Opps. Uninitiated, sorry
--
Graham.

%Profound_observation%

Graham. coughed up some electrons that declared:




* Picture tube may explode if the unprotected thin rear of the tube is
broken. (Breaking the nipple is the standard disposal method.) The
large vacuum in the tube causes implosion, and the broken glass can
bounce back out explosively.


I'm not at all happy with the idea that breaking the area near the
EHT connector is safe, in fact IMHO I can't think of a more
dangerous way to destroy a tube.

The standard way of destroying the vacuum is to crack the *neck*
with a small hammer ot the handle or a long screwdriver.
It is easy to do because the glass is thin at this point, and the
narrow neck ensures that the air rushes in comparatively
slowly with a hiss rather than Earth-shattering KABOOM

Agree, having dispatched several dozen at Imperial College this way.

Safety goggles, leather gloves, big long screwdriver, large hammer.

Bang screwdriver through the case centre rear of top, push in and feel for
the neck of the tube, then a good tap with the hammer. Pop and a hiss later
and job done. Screen turning light grey in patches is a secondary
confirmation all went well.

Cheers

Tim

Graham. wrote:
"PM" wrote in message
...
NoSpam wrote:
wrote:
Feedback welcome...
... snipped
snipped some more

- "Propped appliance can fall on child or pet" is not unique to a TV
and is OTT.
Likewise "ill fitting spanners" is not the fault of the washing machine.
(Unless they come with them?)

I strongly disagree with you, this is a wiki for the in-initiated, and both
warnings should remain.
Many modern CRT sets become very unstable if you attempt to remove
the back cover with the set on its stand. The weight of the tube makes
the whole escutcheon rake forward, along with the centre of mass.

As for the other point about ill-fitting tools in white goods, I would be
in favour of removing the word "minor" in "minor injuries" as slashed
wrists have been known to be fatal!


I don't wish to be confrontational, but following this line will lead to
warnings that standing on one leg can lead to falling over and injury
due to imbalance. A little bit of natural selection is a good thing.

Graham. wrote:
* Picture tube may explode if the unprotected thin rear of the tube is
broken. (Breaking the nipple is the standard disposal method.) The
large vacuum in the tube causes implosion, and the broken glass can
bounce back out explosively.


I'm not at all happy with the idea that breaking the area near the
EHT connector is safe, in fact IMHO I can't think of a more
dangerous way to destroy a tube.

The standard way of destroying the vacuum is to crack the *neck*
with a small hammer ot the handle or a long screwdriver.
It is easy to do because the glass is thin at this point, and the
narrow neck ensures that the air rushes in comparatively
slowly with a hiss rather than Earth-shattering KABOOM

When I were a lad the standard method was to crush the glass nipple in
the centre of the connector. I don't think anybody is recommending
breaking anything near the EHT connector.

On Tue, 09 Dec 2008 09:25:40 +0000, NoSpam
wrote:

- May want to discuss degassing by crushing the nipple

What the hell is that? I've not had to do it for quite a few years but
I've always used a reel to reel bulk tape eraser.


--

"Mike" wrote in message
...
On Tue, 09 Dec 2008 09:25:40 +0000, NoSpam
wrote:

- May want to discuss degassing by crushing the nipple

What the hell is that? I've not had to do it for quite a few years but
I've always used a reel to reel bulk tape eraser.


Degassing Mike,
You are thinking about degaussing.

--
Graham.

%Profound_observation%

"NoSpam" wrote in message
...
Graham. wrote:
* Picture tube may explode if the unprotected thin rear of the tube is
broken. (Breaking the nipple is the standard disposal method.) The
large vacuum in the tube causes implosion, and the broken glass can
bounce back out explosively.


I'm not at all happy with the idea that breaking the area near the
EHT connector is safe, in fact IMHO I can't think of a more
dangerous way to destroy a tube.

The standard way of destroying the vacuum is to crack the *neck*
with a small hammer ot the handle or a long screwdriver.
It is easy to do because the glass is thin at this point, and the
narrow neck ensures that the air rushes in comparatively
slowly with a hiss rather than Earth-shattering KABOOM

When I were a lad the standard method was to crush the glass nipple in the
centre of the connector. I don't think anybody is recommending breaking
anything near the EHT connector.

Strictly speaking that is called the "pinch"

I wonder if the OP meant the tube base, or the EHT cavity connector
(which I have heard referred to as the nipple)
--
Graham.

%Profound_observation%

NoSpam wrote:
Graham. wrote:
* Picture tube may explode if the unprotected thin rear of the tube is
broken. (Breaking the nipple is the standard disposal method.) The
large vacuum in the tube causes implosion, and the broken glass can
bounce back out explosively.


I'm not at all happy with the idea that breaking the area near the
EHT connector is safe, in fact IMHO I can't think of a more
dangerous way to destroy a tube.

The standard way of destroying the vacuum is to crack the *neck*
with a small hammer ot the handle or a long screwdriver.
It is easy to do because the glass is thin at this point, and the
narrow neck ensures that the air rushes in comparatively
slowly with a hiss rather than Earth-shattering KABOOM

When I were a lad the standard method was to crush the glass nipple in
the centre of the connector. I don't think anybody is recommending
breaking anything near the EHT connector.

No - I've rephrased to clarify.

* Picture tube may explode if the unprotected thin rear of the tube is
broken. (Breaking the nipple on the end of the neck is the standard
disposal method.)


NT