MRF
16/22
MF 55-GB 1.21
49
14 Fault analysis
A. Furnace does not heat up
Æ
Check 1: A visual inspection of the
elements inside the chamber for
signs of failure
1. The
HEAT
light
is
ON
Æ
The element circuit has
failed
Æ
Check 2: Isolate the MRF 16/22 from
the electrical supply; disconnect the
element circuit from the transformer
secondary windings, check the
continuity of the element circuit.
Open circuit indicates element
failure.
Æ
The controller shows
a
very high temperature
and code S.br
Æ
The thermocouple has failed and
gone open circuit
Æ
The door switch may be faulty or
need adjustment
Æ
The thyristor fuse may have blown
Æ
The controller shows a
low temperature
Æ
The power thyristor could be failing
to switch on due to internal failure,
faulty wiring from the controller, or
faulty controller
Æ
The fault light on the
control panel is on
Æ
The thermal cutout on the case or in
the transformer has activated
Æ
The
SUPPLY
light is
ON
Æ
The controller may be faulty or not
receiving a supply due to a blown
instrument circuit fuse, faulty switch
or a wiring fault
2. The
HEAT
light
is
OFF
Æ
There
are no
lights
glowing
on the
controller
Æ
The
SUPPLY
light is
OFF
Æ
Check the supply fuses and any
fuses in the furnace control
compartment
3.
Fuse blows
or
earth leakage
device
trips
as
soon as furnace
starts to heat.
Æ
Element insulating mica
washer has failed.
Æ
Check: Isolate the MRF 16/22 from
the electrical supply; remove the top
access panel and element tails MW
shield lid. Disconnect element circuit
form transformer secondary
windings. Check resistance between
element tails and brickbox case. If
this is low (below 500k
then
remove element braids and check
each element tail until the one
causing the low resistance is
identified. Replace mica washer
(refer to section 13.9 for mica
washer replacement) and recheck
resistance.
