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the other leg of the heat relay coils, which then close electronic switches in the 24 VAC circuit to
provide current to the ignition module. Circuitry in the ignition module sends 24 VAC to the gas
valve via a normally closed high-limit switch (and, in fryers with built-in filtration systems, a
normally closed drain safety switch). Simultaneously, the module causes the ignitor to spark for 4
seconds to light the burner. A flame sensor verifies the burner ignition by measuring the flow of
microamps through the flame. If the burner does not light (or is extinguished), current to the
ignition module is cut, the gas valve closes, and the ignition module “locks out” until the power
switch is turned off and then back on. A probe monitors the temperature in the frypot. When the
programmed setpoint temperature is reached, resistance in the probe causes the heat cycle circuitry
in the controller to cut off current flow through the heat relay. This in turn cuts off the 24 VAC to
the ignition module, causing the gas valve to close.
INTERFACE BOARDS
All fryers in this series have an interface board located in the component box located behind the
control panel. The interface board provides a link between the controller/computer and the fryer’s
individual components without requiring excessive wiring, and allows the controller to execute
commands from one central point. The H50 Series of fryers has been in production since 1983.
Consequently, servicers are likely to encounter three different interface board designs. Although the
boards differ slightly in appearance, basic functioning and electrical connections are the same from
one to another. In the earlier design 806-3398 interface board (used between June 1996 and July
1999), the diagnostic LEDs are arrayed in a row across the bottom of the board as shown in the left-
hand illustration below. In later design 806-3398 interface boards (and in the 106-0396 interface
boards that replaced them in current production fryers), the LEDs (labeled D1 though D7) are
scattered around the board as shown in the right-hand illustration. The primary difference between
the earlier design boards and the later design boards is the combining of the separate blower motor
relay (K4) and the heat relays (K1 and K2) into a pair of replaceable relays (K2 and K3) in the latter.
Also, the 106-0386 interface board has an additional fuse located in the upper right hand corner.
Prior to June 1996, a board with replaceable relays very similar in appearance to the 106-0386 board
was used. It is distinguished from the 106-0386 board by the absence of fuses.
NOTE: Although the printing on many boards indicates 2 Amp fuses, 3 Amp fuses (P/N 807-3843)
must be used.
K4
K1 K2
SOUND
1
2
3
GND
GND
V2D
PWR
AD
AS
V2S
GND
V1D
PWR
ALR
V1S
GND GV PWR
AL 12V
AIR
24V AL
PWR
GV
GND
J2
EARLIER DESIGN INTERFACE BOARD P/N 806-3398
GND
12 6 3 45
J3
3 6 9 12
2 5 8 11
1 4 7 10
J1
3 6 9 12
2 5 8 11
1 4 7 10
15
12963
14
11852
13
10741
BLOWER
MOTOR
RELAY
K3 K5
HEAT
RELAY
HEAT
RELAY
K4
K1
SOUND
1
2
3
GND
GND
V2D
PWR
AD
AS
V2S
GND
GV
PWR
12V
AIR
24V
PWR
GND
V1D
PWR
ALR
V1S
GV
GND
J2
LATER DESIGN INTERFACE BOARDS P/N 806-3398 and 106-0386
GND
J3
3 6 9 12
2 5 8 11
1 4 7 10
J1
3 6 9 12
2 5 8 11
1 4 7 10
15
12963
14
11852
13
10741
K2 K3
HEAT
RELAY
AND
BLOWER
MOTOR
RELAY
D1
D2
D3
D4
D6
D7
Blower
Motor
2 Amp
D5
HEAT
RELAY
AND
BLOWER
MOTOR
RELAY
F2 Ignition
2 AMP Module
This Fuse is NOT
present on 806-3398 IFB.