10
Service
Caution
Only qualified personnel should con-
duct service to the furnace.
WARNING
Always disconnect power cord from
the power supply before servicing
instrument.
All Fisher Isotemp 550 Series Muffle Furnaces use wall
heaters. The Model 550-58 and 550-126 also incorporates
a floor heater to maintain uniform heating. The following
sections describe procedures for replacing a heater or the
control thermocouple.
Replacing a Heater
To replace a defective heater, proceed as follows:
1.
Disconnect power cord from the electrical out
let.
2.
Open chamber door and allow door to remain
open throughout heater replacement.
3.
Remove the screws that secure the perforated
metal back panel of the furnace main chassis.
Remove the panel and set it aside.
4.
Loosen two heater terminal screws located on
the terminal barrier strip. Straighten the lead
screws.
5.
Carefully withdraw the defective heater from the
chamber. Ceramic wool insulated surrounding
heater wires will fall into the furnace chamber.
Remove it and set it aside for later use.
6.
Carefully install the replacement heater be
reserving the procedure in step 5 above.
7.
Carefully re-attach the heater terminals by
reversing step 4. Then refill the holes around
heater leads with ceramic wool preserved from
step 5.
8.
Re-install perforated metal back panel of the fur-
nace.
9.
When the above steps are complete, return the
power cord to the electrical outlet.
Note
Allow chamber to cool to ambient tem-
perature before attempting repair.
Caution
Heater panel material is fragile.
Exercise care when inserting replace-
ment panels into the furnace chamber.
Likewise, bend or flex the heater leads
gently when necessary.
