Appliance repair hazards

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

Note this is not a list of all hazards of appliances, but rather those that specifically apply to repairing them.


Common risks

Some risks are common to all mains appliances:

  • Shock if plugged in
  • Basic wiring faults

Shock risk is often reduced with an RCD or isolating transformer, or by simply not working on live equipment.


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
  • Fitting the wrong internal fuse can result in the interlock failsafe system not operating

Old microwaves

Old machines from the beginning of the '80s and before can have:

  • unsafe interlock system.
  • carbon loaded rubber door 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 seen occasionally, and in a minority of cases can continue cooking with the door part way open. These are hopelessly unsafe.

Damaged microwaves

The mains risks are:

  • missing or damaged door grille (cooks the user)
  • warped door
  • missing door 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 hand, foot, child or pet. CRT sets have their centre of gravity close to the front, and some are barely stable when the rear cover is removed. They often surprise casual repairers by toppling unexpectedly.
  • Live chassis were common until the late 1980s. Connecting external devices to these sets can shock, or in the case of headphones can kill. (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 shaped pinch on the end of the neck is the standard disposal method.) The large vacuum in the tube causes implosion if it shatters, and broken glass can bounce back out explosively.
  • If replacing or repairing an aerial socket on a CRT set, ensure the replacement is capacitor coupled and avoid compromising the capacitor isolation. Otherwise the aerial system becomes live with many sets.

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

Historic TV

Very old TVs are different to modern kit in some respects, especially in picture tube safety.

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.

Pre-1960 picture tubes that use a separate plate glass shield for protection 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 used a lethal 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 often 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