Basic Operation; Operating Controls - Maytag MFR Series Service Manual

The control boards used in the MFRxxPDC
coin washers provides electrical power
distribution and switching to the operating
components of the washer. A single control
board contains a power supply for the
microprocessor and operating integrated
circuit "chips", a number of low-voltage relays
to switch power to off-board components
(drain valve motor, fill valve solenoids, door
lock components and the motor contactor. A
liquid crystal display screen is used to provide
visual feedback to the user. A six button (PD)
or twenty-two button (PN) membrane switch
assembly provides user interface for cycle
selection and technician interface for service
diagnosis and programming functions.
The input voltage to the Control board power
supply is 208 to 240VAC. A transformer on the
board drops this down to the several rectified
circuits to provide DC for the control circuits
and the relay coil circuits. Individual bridge
rectifiers are on the board for the door lock
solenoid and the door release solenoid coils.
A low voltage DC supply around 12 volts
is applied to external switches for the door
lock assembly coin vault and to an optical
coin sensor on the coin acceptor. There
are connections on the board for two coin
sensors.
A replaceable / reprogrammable EPROM
chip provides the operating directions for the
control board. This allows for cycle changes
and system up-grades by changing a chip
(and re-loading the new program).

BaSiC OpeRaTiOn

OpeRaTinG COnTROlS

3-1
While all models use the same control board,
MFR18PDC and MFR25PDC are 120VAC
washers. These two models have a built in
step-up transformer to change 120VAC line
voltage to 240VAC, which is required by the
control board, the drain valve motor, water
valve coils, motor contactor, and the door lock.
NOTE: Applying 208-240VAC to the Terminal
Block of the MFR18-25 washers will cause
immediate damage to the control board and
possibly other components as well.
A solid state water level control is mounted
on the control board to monitor the washer's
water level. A small diameter air-tight hose is
connected from the drain valve to the control
board for this purpose.
There are no serviceable components, except
for the EPROM chip and the fuse, on the
control board. In the event of a failure of the
control board, replace the entire board.
First, disconnect power before replacing the
EPROM on the control board. The EPROM
is located in a socket toward the right end
of the board (as viewed from the front of
the washer). Pay particular attention that
the "notch" on the end of the chip faces the
right end of the board. Installing an EPROM
backwards will burn the EPROM and damage
the Control board!
nOTe: When prying the EPROM off of its
socket make sure that the screw driver is
placed between the socket and the chip not
between the socket and the control board, or
damage will occur to the socket.