Figure 1 - Pump Handle Circuit
HOW TO CORRECT PROBLEMS IN THE PUMP HANDLE CIRCUIT
PROBLEM CAUSE ACTION
1. There is no a. There is a bad pump a. Test the switch for
response handle switch. continuity. If bad,
from the pump replace.
handle. b. There is a defective b. Install a new barrier
barrier. and test.
c. There is a bad connec- c. Check all connectors.
tion. Repair or replace.
d. I/O Board is defective. d. Swap the I/O Board
with a known good I/O
Board to verify.
e. Defective CPU e. Replace CPU
2. The wrong a. The pump handle barrier a. Refer to the I/O
price per is in the wrong connect- section of this Man-
volume or on the I/O board. ual for connector
appears on location.
the display
when the pump
handle is
lifted. b. The CPU board is defect- b. Replace the CPU
ive. board.
3. There is a a. There is a bad pump a. Test the switch
constant handle switch. for continuity.
handle signal If bad, replace.
at the b. The pump handle barrier b. Install a new
console. is defective. barrier.
c. The CPU board is c. Zero the memory
defective. on the CPU. If
problem continues,
replace the CPU
board.
d. Ribbon cable on the I/O d. Replace I/O board.
board is shorted.
The pump handle barrier circuit was designed to provide an intrinsically safe link between the CPU board and the pump handle switch. The pump handle circuit is divided into two sections, the barrier section and the CPU comparator section.
The barrier section provides limited power feedback from the pump handle switches to the comparator section on the CPU board. It limits the current level so no spark can occur below the flame deck.
The comparator section senses the current flow through the pump handle switch and converts it to a logic level signal for the CPU to recognize.
Circuit Description
The dispenser uses a +12VDC supply to operate the pump handle circuit. Each pump handle uses a microswitch located on the pump handle casting. Two wires connect the microswitch to the barrier. The barrier contains 4 wires (two for Hose A, Side 1, and two for Hose B, Side 2). These four wires connect the pump handle signal to the I/O board through the barrier providing an intrinsically safe circuit. The pump handle signal is then routed to the comparator chip on the CPU board via the 20 conductor ribbon cable WH1 (JP1). Refer to Figure 1 for the circuit path.
Once the comparator chip on the CPU board senses that the switch has been closed, it drops the logic voltage signal and sends it to the microprocessor, creating a pump handle signal on the CPU board.
Figure 1 - Pump Handle Circuit
A symptom of a bad barrier is a constant handle signal. If the handle call signal goes out when the connector is removed from the I/O board, check the handle switch and barrier for the problem.
A spare barrier or one from a different I/O board position in the head can be swapped to check for proper operation. To do this, remove the connector on the I/O board in question. Plug the new barrier in its place. Activate a handle signal and check for proper operation.
Test the continuity of the microswitch for the pump handle with a volt meter to determine if the switch is bad.
CAUTION: Make sure pins are not shorted together on any chip while making voltage measurements. Chip damage can occur.
A second way to check the operation of the handle signal is by tracing the signal path. To measure the signals to and from the comparator, the following procedure must be followed:
1. Locate U4 & U5 on the CPU board. See Figure 2.
Figure 2 - CPU Board
2. Place the meter ground lead on the logic ground test point (TP6). See Figure 2 above.
3. Place the positive lead on the pins according to the chart below, to verify proper comparator operation.
HOSE 1A Input U4 pin 5 Output U4 pin 2
HOSE 1B Input U4 pin 7 Output U4 pin 1
HOSE 1C Input U4 pin 9 Output U4 pin 14
HOSE 1D Input U4 pin 11 Output U4 pin 13
HOSE 2A Input U5 pin 5 Output U5 pin 2
HOSE 2B Input U5 pin 7 Output U5 pin 1
HOSE 2C Input U5 pin 9 Output U5 pin 14
HOSE 2D Input U5 pin 11 Output U5 pin 13
Input Voltage should be:
Output Voltage should be:
These readings will vary depending on your meter.