BOFI XLT TS Series Manuale utente
Service Manual
XLT TS Series Conveyorized Oven
XD9011-TS
Rev C - 05/2008
© 2008 BOFI Inc.
BOFI™
P.O. Box 9090
Wichita, KS 67277-0090
Phone: 1-316-943-2751
Fax: 1-316-943-2769
www.x tovens.com
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XLT TS Series Service Manual 3
WARNING & SAFETY INFORMATION
FOR YOUR SAFETY
Do not store or use gasoline or other flammable
liquids or vapors in the vicinit of this or an other appliance.
WARNING: Improper installation, adjustment, alteration, service or maintenance
can cause propert damage, injur , or death. Read the installation, operating and
maintenance instructions thoroughl before installing, using, or servicing this
equipment.
WARNING: In the event a gas odor is detected, shut off the gas at the main shutoff
valve immediatel . Contact our local Gas Compan or supplier.
WARNING: Disconnect electrical input power to the unit before performing an
maintenance.
Before trouble-shooting the oven make sure that the oven is plugged in to a
120VAC electrical power outlet. Check to see that the breaker hasn’t been tripped. The
circuit should be a 20 amp circuit. Sometimes it is helpful to measure the voltage at the
outlet or plug a light into the outlet to verify the power. All fuses should be checked.
The fuse caps are the quarter turn bayonet style. Use a continuity checker on removed
fuses if a visual inspection is indeterminate. Fuses are used to protect both the inputs and
outputs of each particular device.
Also check to see if the gas supply is adequate. The 3/4" gas hose should be
connected to the oven and the shutoff valve fully opened. Make sure that the quick-
disconnect is properly connected. A full flow style shutoff valve (with pressure tap)
should be used and the gas pressure should be measured. For proper operation the gas
inlet pressure to the oven must stay between 8.0" to 12.0" WC for natural gas and 11.0"
to 14.0" WC for propane gas. Measure the gas pressure with all gas appliances off such
as furnace hot water heater ovens etc. and all gas appliances on. See the Rough-In
section in the Installation and Operation Manual for layout details. Also remember that
anytime the gas hose has been disconnected it will take time to purge the air from the gas
train.
Finally check to see that the oven is fully assembled. All of the fingers must be
properly installed. Incorrect or incomplete finger placement can cause a “windy”
condition that can cause the pilot or burner not to light similar to a cigarette lighter
outside on a windy day.
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Table of Con en s
Description .......................................................................................................................... 5
Operation............................................................................................................................. 5
Fan Subsystem..................................................................................................................... 6
Fan Subsystem Trouble-Shooting ....................................................................................... 6
Burner Subsystem ............................................................................................................... 7
Combustion Blower Trouble-Shooting ............................................................................. 12
Modulating Valve and Signal Conditioner Trouble-Shooting .......................................... 12
Temperature Control Trouble-Shooting............................................................................ 13
Instruction to switch from Fahrenheit to Celsius readout ................................................. 17
Conveyor Subsystem......................................................................................................... 18
Conveyor Control Trouble-Shooting ................................................................................ 19
Dart MD10P Controller Programming Procedure ............................................................ 20
Conveyor Belt ................................................................................................................... 21
Electrical Schematics ........................................................................................................ 35
XLT TS Series Service Manual 5
Descrip ion
XLT Ovens consist of 3 basic subsystems: the Fan Burner and Conveyor
subsystems. All of the ovens have 3 switches which turn each of these on. The fan
switch supplies power to the burner and conveyor switches so it must be turned on first.
Note that the 3270 ovens have an additional control box on the left side of the oven. This
oven can be controlled from either side but the opposite side set of switches must be left
on. The Parts Manual shows part locations and exploded views.
The fan switch supplies power to the oven fan motor the control box cooling fan
the cool-down timer relay the temperature control the burner switch and the conveyor
switches. The cool-down relay timer is connected to power when the oven is plugged in
and provides 30 minutes of power to the oven fan after the fan switch is turned off. The
oven fan has an internal centrifugal switch that completes the circuit to the burner blower
motor. The burner blower motor in turn has an internal centrifugal switch that completes
the circuit to the burner ignition control.
The burner switch applies power from the fan switch to the oven fan motor
centrifugal switch. The conveyor switch applies power from the fan switch to the
conveyor control. See the electrical schematics.
There are a few differences between the natural gas model ovens and the propane
(LP) gas models. Electrically they are the same. The burner orifice modulating valve
and combination gas valves are different for the two models. The propane models have
smaller burner orifices and higher gas pressure ranges. See the A4200 burner drawing in
the Parts Manual for orifice size information. The modulating valves have different
internal coils and are marked M420B for natural gas and M420BH for propane. The
combination gas valves are field convertible (Honeywell kit number 393691) and have
stainless steel pressure regulator springs for natural gas and red pressure regulator springs
for propane (LP).
Opera ion
1) When the Fan Switch is turned on:
a. The main fan motor should run.
b. The cooling fan on the side of the control box should run.
c. The temperature control should display the actual temperature.
2) When the Burner Switch is turned on;
a. The combustion air motor should spin.
b. The pilot gas valve should open and you should hear a “ticking”
noise. This is actually a high voltage spark arcing across tips.
c. The main gas valve should open and the burner should light.
d. The combustion should be audible and the actual temperature
should rise steadily.
e. To verify burner ignition remove the front panel and you should
see a blue flame under the lower fingers near the back of the unit.
There is also a flame inspection window in the burner.
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3) When the Conveyor Switch is turned on;
a. The conveyor control should come on and display the desired
conveyor time.
b. The conveyor belt should move slowly.
Fan Subsys em
The Fan subsystem consists of a fan motor (M1) and capacitor (C1) a fan blade a
control box cooling fan (M2) and a cool-down timer relay (R1). The oven fan motor is a
single phase 120VAC 1740 RPM motor. It requires a capacitor to run and has an
automatic internal thermal overload. It is usually electrically reversible to accommodate
either the CW or CCW fan blades. When replacing this motor be sure to verify proper
fan rotation. See oven decals and drawing A5000 in the Parts Manual for rotation and
fan installation details. The capacitor is remotely located in the control box. The fan
motor also has an auxiliary internal centrifugal switch which completes the circuit for the
burner blower motor. This is a burner safety feature that must NOT be defeated. The fan
motor is protected by fuse F1. The control box cooling fan keeps the electrical
components in the control box cool and it must have its filter cleaned frequently.
Fan Subsys em Trouble-Shoo ing
Symptom Possible Case Solution
Fan not
running
No power Check Fuse F1.
Check voltage from switch S1.
Check voltage from relay R1.
Check voltage at motor leads.
Fan not
running
Bad capacitor Check capacitor C1 or replace with known good
capacitor.
Fan not
running
Bad automatic
internal overload
Make sure motor has cooled down clean debris
from motor cover vent holes check to see that
motor bearings rotate freely.
Noisy fan Loose fan blade set
screws
Remove back wall and tighten set screws on shaft
flats make sure that fan position is 8.5" away
from the back wall. Use new set screws.
Noisy fan Bad bearings With power removed spin shaft by hand and feel
for bearing roughness and noise.
Noisy fan Shaft rubbing Remove the back wall assembly. Remove the fan
blade from the motor shaft and inspect the motor
shaft to back wall sheet metal clearance. Adjust
as necessary.
Noisy fan (very
loud)
Fan blade rubbing Remove the front panel and 1 center upper and 1
center lower finger. Visually check the fan blade
to see if it is rubbing the fan shroud. Adjust the
fan motor bracket or back wall as necessary.
XLT TS Series Service Manual 7
Burner Subsys em
The Burner subsystem consists of a forced air burner and gas train a pilot valve
(V2) a main valve (V1) a burner control (BC) a temperature control (TC1) a
thermocouple (T/C) a modulating valve (V3) and signal conditioner (SC1) and a 24V
transformer (XR1). When the burner switch S2 is turned on power is applied from S1 to
the common terminal of the output relay of the temperature control. The output 2 relay is
closed by the temperature controller (high alarm auto reset programmed) and provides
power to the primary of the 24V transformer and also to the burner blower motor (M4).
The transformer provides the necessary voltage for both the signal conditioner and the
burner control. The burner blower motor (M4) must be spinning for the internal
centrifugal switch (S4) to complete the circuit to the burner control.
The thermocouple provides a temperature feedback to the temperature control.
The temperature control provides a 4-20 MA output to the signal conditioner. The signal
conditioner in turn proportionately provides a 2-20 VDC 400 MA power output to the
modulating valve. If the thermocouple either breaks or becomes out of range the
temperature controller will sense and force the output off.
The input of the temperature controller is protected by fuse F2 and the output is
protected by fuse F10. The transformer and burner blower motor are protected by fuse
F3. Fuse F9 protects the input of the signal conditioner while fuse F6 protects the output
to the modulating valve. Fuse F4 protects the pilot valve (V2) and fuse F5 protects the
main valve (V1). The combination gas valve has the pilot valve the main valve and the
pressure regulation contained within it. The knob on top of the combination valve must
be left in the ON position. See Figure 1. The lamp (L1) on the control box if present
indicates whether the flame sensor in the burner pilot is hot.
When the burner control receives power the pilot valve opens and the spark
generator operates. If the pilot burner lights; the burner control senses flame current
through the spark wire the spark generator then shuts off and the main valve opens. The
burner control continues to monitor the pilot flame current. If the pilot burner does not
light after 90 seconds the burner control locks out and must be reset by switching the
burner switch off and then back on. If the power is interrupted the burner restarts when
power is restored. If there is a pilot flame failure (no current sensed in the spark wire) the
burner control starts trial for ignition again.
The modulating gas valve is plumbed in series with the main gas valve. See
Figure 3. In normal operation the main gas valve stays on all the time while the
modulating valve is controlled by the temperature control. If there is a large difference
between the actual temperature measured by the thermocouple and the set point
temperature the temperature controller has a high output value to the signal conditioner.
The signal conditioner in turn produces a corresponding high voltage output to the
modulating valve which opens up to the maximum and causes the burner to operate at
maximum. As the temperature difference narrows the outputs similarly decrease causing
the burner to fire at a reduced rate. There is enough heat loss even in an idle oven for the
modulating valve to always be open somewhat. Therefore the main valve is also always
open and the burner control only needs to operate the ignition cycle once.
The modulating valve usually requires no adjustment. There are two bypass
needle valves on the opposite sides of the valve. The one that is inaccessible is always
closed by default. The accessible one is also usually closed but may be slightly open
depending on the model of oven. Another adjustment is the low fire bias screw which is
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the brass plated screw located under the oval cap on top of the modulating valve. The
plastic screw under the cap is a plunger stop and is not adjustable. The function of the
low fire bias screw is to cause the required signal conditioner voltage range to change and
match the optimum range produced by the temperature controller output. In general this
screw is usually within a full turn of all the way out and does not require adjustment.
Also note that the modulating valve must be installed in an upright orientation.
The manifold pressure should be measured when the oven is operating. The best
time to do this is when the oven is cold. With the oven disconnected from power
connect a 1/8" NPT brass hose barb fitting to the combination valve outlet pressure tap
port. Adjust the manometer scale to zero inches water column and connect the U-tube
manometer hose to the barb. Connect the oven to power and turn on the fan switch and
then the burner switch. After the oven ignites the manifold pressure reading should be
3.5" for natural gas or 10.0" for propane gas. Adjust the pressure regulator screw as
required. The pressure regulator screw is located under a slotted cap screw on the inlet
side of the combination valve. Be sure to plug the outlet tap port after measurements and
adjustments are complete. It is always a good idea to leak check the gas train and pilot
line after servicing the gas train and burner components.
Figure 1: Combination Gas Valve
XLT TS Series Service Manual 9
It is sometimes necessary to check the pilot gas pressure especially for propane
ovens. In order to do this remove the pilot line between the combination gas valve and
the burner. Loosen the fittings on each end of the pilot line (see Figure 2). Install a
pressure tap tee in the pilot line. This can be a permanent fitting with a removable cap on
the center port of the tee or temporary rubber hose sections with a barbed tee. Attach a
manometer to the center port of the tee to monitor the pilot pressure. Remove the main
gas valve fuse from the control panel. This will cause the oven to fire only the pilot
circuit. Turn the oven on and adjust the pilot pressure by turning the pilot pressure
adjustment screw (see Figure 1) clockwise to reduce pressure. Conversely turning the
screw counterclockwise will increase the pressure. Adjust to 5-7" for natural gas or 8-10"
water column for propane. Also if available use a micro-amp meter to check the current
(2.0 micro-amps min.) in the flame sensor circuit. The flame inspection window can be
used to visually see the pilot light presence and color. At minimal pressure the flame will
be small or non-existent (out). Too much pressure and the flame will be large and
yellow. Typically the screw is turned in clockwise until the flame almost disappears and
then backed out slightly counterclockwise until the flame is blue and substantial.
When finished with the pilot pressure adjustment remove the hoses then cap or
remove the tee and finally check for gas leaks with a soapy water solution. Use a mix of
2/3 liquid soap and 1/3 water. A small brush can be used to paint the joints with this
soapy mixture. An electronic leak detector can also be used instead. Be sure to replace
the main gas valve fuse and the pressure adjustment screw cover cap(s) on the gas valve.
Figure 2: Gas Train Assembly & Burner
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XLT ovens employ an ignition control to initiate and monitor the operation of the
oven’s burner. Monitoring is accomplished by a flame sense feedback circuit. The flame
sense current loop is completed when the pilot flame 'paints' the spark electrode.
Electrons are then conducted by the flame from the spark wire to ground. When the
flame no longer touches the electrode or the electrode becomes encrusted with soot (LP
gas operation) the current loop is broken or weakened and then the ignition control shuts
off the valves.
This flame sense current can sometimes be strengthened or improved by adding a
ground wire between the burner and the combination valve. The primary path for the
ground is the pilot line back to the valve but loose or rusty connections in the gas train
burner casting orifice holder and/or flame sensor bracket fasteners can cause flame
sense problems. Of course the pilot orifice size pilot pressure and air shutter setting
also affect proper pilot flame adjustment.
For direct spark burners (if equipped) the flame still needs to paint the sense wire
but the flame base must also be attached to the end of the burner casting. It may be
necessary to adjust the air shutter (usually closed) to make the flame attach to the burner
casting end. The flame is also much more stable especially in 'windy' conditions when
it is attached to the casting end. For direct spark burners the auxiliary wire is even more
helpful since the pilot is not present.
There is a corrugated Flame Retention Ring inside the burner casting at the end of
the burner. This is also known as a 'bluff body' and its purpose is to change the gas-air
velocity and allow the flame to attach to the end of the burner thereby helping
completing the flame sense circuit.
Indice
