52
FORM 160.54-M1
ISSUE DATE: 10/25/2019
SECTION 4 - MICROBOARD 031-02430-000 AND 031-02430-001
JCI COMPANY CONFIDENTIAL
JOHNSON CONTROLS
The part number of the BRAM (U52) in the 031-02430–
001 board is 031-02565-000 and its size is 128KB. It
is installed in a 32-pin socket. Program Jumper JP14
is a removable 2-pin shunt type jumper. The 128KB
BRAM requires the shunt be NOT INSTALLED and
the board is supplied in this configuration. If the shunt
is installed on JP14, it would apply DC power to an in-
correct pin on the 128KB BRAM and the board would
not function. The 128KB BRAM is required for MV
SSS, MV VSD, and those VSD that communicate with
the microboard using Modbus serial communications
protocol.
The 031-02430–001 board with 128KB BRAM re-
quires software that has “BRAM size detect” capabil-
ity. If it does not have this capability, the board will not
function. YK chiller software version C.OPT.01.15.
xxx (and later) has this capability and is required.
When replacing a 031-02430-000 Microboard with a
031-02430-001 Microboard in applications other than
MV SSS, MV VSD and VSD Modbus, the smaller
BRAM from the 031-02430-000 board can be trans-
ferred to the 031-02430-001 Microboard. See BRAM
transfer exception in Microboard Service Replacement
later in this section.
Watchdog Circuit
The Watchdog circuit performs two functions as fol-
lows:
• Power failure detection
• Program latch-up detection/prevention
The Watchdog Circuit monitors the +5 VDC from the
power supply and the +3.3 VDC from the onboard reg-
ulator to determine when a power failure is occurring.
If the +5 VDC decreases to the threshold of (+4.75
VDC to 4.5 VDC) or the +3.3 VDC decreases to the
threshold of (3.04 VDC to 2.8 VDC), a reset is issued
to the microprocessor and the chiller shuts down. When
power is restored, the white screen is displayed and the
boot-up is performed as described above. When the
graphic screen is displayed, the message CONTROL
PANEL – POWER FAILURE is displayed.
The Watchdog Circuit also ensures that the entire pro-
gram is being executed and that the program has not
latched-up, bypassing important safety checks. The
Watchdog circuit is a timer that times-out if not given
a reset pulse within its time-out period (1 to 2.25 sec-
onds). To prevent a time-out, the microprocessor sends
a reset pulse to the Watchdog circuit every time the
complete program has been executed. Since it takes
less than 1 second to perform the entire program, the
Watchdog circuit doesn’t time-out under normal opera-
tion. However, if the entire program is not executed or
something prevents the microprocessor from sending
the reset pulse as described below, the Watchdog cir-
cuit times-out and sends a reset to the microprocessor,
initiating a re-boot. If running, the chiller shuts down.
The display momentarily blanks and white screen is
displayed while the boot-up program executes as de-
scribed above. When the graphic screen is displayed,
either of two messages is displayed depending on the
type of Watchdog shutdown as explained below.
There are two different watchdog initiated shutdowns;
a HARDWARE watchdog initiated shutdown and a
SOFTWARE watchdog initiated shutdown.
In the HARDWARE watchdog initiated shutdown, a
program problem, on-board noise or hardware problem
could prevent the watchdog time-out. If this occurs, a
re-boot is initiated and when the graphic screen is dis-
played, CONTROL PANEL – POWER FAILURE is
displayed.
In the SOFTWARE watchdog initiated shutdown, the
program intentionally initiates the reboot because it
has detected program interruption. After the re-boot,
WATCHDOG – SOFTWARE REBOOT is displayed
on the graphic screen.
Program Jumpers/Program Switches
The Program Jumpers and Program Switches are used to
alter the program operation or configure the microboard
hardware for specific operation. This allows the Pro-
gram and Microboard to be universal for all standard
for the function of
each jumper and switch. The position of some jumpers
can be determined by the Service technician to meet
the desired operation. Others must be positioned ac-
cording to the requirements of the size, type or style of
components and thus are determined by the YORK fac-
tory. The jumpers are plastic sleeves with metal inserts
that are inserted over 2-prong or 3-prong conductors.
The Program Switches are miniature switches that are
placed in either the ON or OFF position.