Lindberg/Blue Mini-Mite TF550 A, Installation And Operation Manual

Page: 20 / 33

Maintenance Mini-
Mite™ Tube Furnace
17
9.5 Temperature Controller Replacement
WARNING!
Disconnect furnace from main power
before attempting any maintenance to furnace or
Its controls.
To replace the temperature controller, complete the
following steps (refer to Figure 5 on page 16):
1. Disconnect main power and switch the circuit breaker (#4 in
Figure 5 on page 16) to the OFF position.
2. Remove the two sheet metal screws located on each side of the
furnace near the lower front (#1 in Figure 5 on page 16). Pull the
control panel forward to access the controller (#5 in Figure 5 on
page 16).
3. Note the terminal connections of the wires and label them for
reattachment. Remove power input and output wires from the
back of the controller. Observe polarity for the thermocouple lead
wire. Red is always negative. Refer to Figure 1 on page 3 for
additional wiring information.
4. Carefully pry the top and bottom of the square collar away from
the sleeve and slide the collar off the back of the sleeve.
5. Pull the controller out through the front of the control panel.
6. Install the replacement instrument by reversing the above
procedure.
9.6 Circuit Breaker Replacement
The control circuitry is protected by two circuit breakers located
at the rear of the furnace (lower left side). When a circuit
breaker opens, a white indicator tab is visible. Check the circuit
for faults and press the circuit breaker switch to reset. Replace
any circuit breaker which does not reset.
9.7 Heating Unit Replacement
WARNING!
Disconnect furnace from main power
before attempting any maintenance to furnace or
its controls.
CAUTION!
This product contains ceramic fiber or
other refractories which can result in the following:
•
May be irritating to skin, eyes, and respiratory tract.
•
May be harmful if inhaled.
•
May contain or form cristobalite (crystalline silica) with
use at high temperature (above 871"C) which can
cause severe respiratory disease.
•
Possible cancer hazard based on tests with laboratory
animals. Animal studies to date are inconclusive. No
human exposure studies with this product have been
reported.
To replace the heating unit, complete the following steps (refer
to Figure 6):
1. Disconnect the main power and open the latch.
2. Remove the eight corner screws connecting the back panel to the
furnace (item #1 in Figure 6). Place the panel near the furnace.
Note:
There are wires connecting the back panel to the furnace.
Be careful to place the back panel next to tho? furnace
without disturbing these wires.
3. Locate the top heating unit terminal block (item #2 in Figure 6).
Label the twisted, solid silver wires which are attached to the
terminal block.
4. Remove the nuts and washers holding the twisted wires to the
terminal block and remove the wires. Remove the ring lugs from
the twisted wires. Save the nuts, washers, and ring lugs for
reassembly.
5. Lift the top heating unit assembly up and away from the furnace
base. Place the assembly on a flat surface with the heating
element facing up.
Note:
To replace the top heating unit, proceed to step 8.
6. Mark and remove the wires from the bottom heating unit terminal
block (item #3 in Figure 6).
7. Remove the thermocouple mounting screws and slide the
thermocouple straight out (refer to Section 9.1 on page 15).
8. Remove the six screws holding the two element hold-down
brackets (item #4 in Figure 6). Remove the hold-down brackets.
9. Lift the heating unit (item #5 in Figure 6) up and out.
CAUTION!
Do not damage the wires extending
from the heating unit.
10. Insert the new heating element. Guide the twisted, solid silver
terminal wires through the slot in the side of the inner furnace. The
bottom of the heating unit will lay flat against the leaf spring.
11. Reassemble the hold-down brackets. Replace the six screws.
12. Connect the heating element terminals to the terminal block
1 4 . Reassemble the furnace.
13.
Drill hole into heating element for the thermocouple, by using a
guide similar to the thermocouple head and a long ¼” drill bit.
See picture for reference .
Note:
To prevent damage to insulation, drill by hand or adjust speed on
drill to the lowest setting.
Figure . See step13 for reference