Middleby Marshall PS200, PS570, PS360 Connections for pickup test, Replacing the Magnetic Pickup

SECTION 3 - SERVICING COMPONENTS

G. Conveyor Control Pickup Test H. Conveyor Motor Test

1.Visually check the pickup for the following:

•The magnet is clean and the bearing is in good condition.

•There are no chips or cracks on the magnet.

•If using a PS350-style pickup (see Figure 14), there is a 1/64” to 1/32” (0-4-0.8mm, or a business card thickness) gap between magnet and hall device.

2Set the multimeter to the VDC scale, then connect the meter probes as shown in Figure 19. The black (-com-

mon) probe should connect to the “COM” terminal on the speed control board, while the red (+VW) probe connects to the “+5V” terminal. +5VDC should be present at all times when the conveyor is operating.

•If +5VDC is present, proceed to Step 3.

•If +5VDC is not present, disconnect the three pickup wires (connected to the “COM,” “SIGNAL,” and “+5V” terminals) and again check for +5VDC.

-If +5VDC is present with the pickup discon- nected, replace the pickup assembly.

-If +5VDC is still not present, replace the con- veyor speed controller.

3.Connect the multimeter’s red (+) lead to the “SIGNAL” terminal; then, disconnect the motor wires from the “- ARM” and “+ARM” terminals. Using a 5/16” open-end wrench, very slowly rotate the motor pickup shaft while observing the multimeter. Two (2) changes from +5VDC to 0VDC should occur for each motor revolution.

•lf the signal is always at 0VDC, go to Step 4.

•lf the signal is always at 5VDC, OR if the signal changes more than 2 times per revolution, replace the pickup assembly.

4.Disconnect the pickup signal wire from the speed con- troller and check for +5VDC at the “SIGNAL” terminal of the controller.

•If +5VDC is present, replace the pickup assembly.

•If 0VDC is present, replace speed control.

Figure 19

Connections for pickup test

1.Disconnect the gear motor wires from the Speed Con- troller terminals (“-ARM” and “+ARM”).

2.Remove the brush retainer caps from the gear motor. DO NOT remove the brushes.

3.Set the multimeter to the lowest Ohm scale. Then, place one meter probe on each brush retaining plate.

BE SURE THAT NEITHER PROBE TOUCHES THE MOTOR CASING.

4.Using a 5/16” open-end wrench, very slowly rotate the motor pickup shaft while observing the multimeter. Dur- ing a 1/2 rotation:

•The Ohm reading should stay betweeen 3-5W.

•There should NEVER be a complete short.

•There should never be a high Ohm reading.

If the motor fails any of these tests, replace the motor.

I.Replacing the Magnetic Pickup

If you need to replace the magnetic pickup on a gear motor shaft:

1.Apply Loctite Removable #242 (or equivalent) sparingly to the threads.

2.Turn the mounting screw until it is finger tight, then turn it an additional 1/4 turn with a wrench.

J. Unshielded Pickup Wires on Early PS360-series ovens

The conveyor speed controller can be affected by electrical noise transmitted by other electrical components or wiring. Early PS360-series ovens used an unshielded connection between the pickup assembly and the control module. On these ovens, the unshielded wiring can pick up the noise and transmit it to the control module. The problem is most easily seen when the conveyor fails during burner spark ignition.

There are two remedies for this problem:

1.Turn the conveyor switch to the OFF position, and then back to the ON position, after the burner has ignited. The controller should reset and allow normal operation. This should be used as a stop-gap measure ONLY to allow the oven to continue operation.

2.Replace the pickup wiring between the control module and the terminal block with a new shielded cable (P/N 42400-0334). When installing the shielded cable, fol- low the color code change shown here:

19

Old Wiring	Shielded Cable
Brown	Black
Orange	Red
Yellow	White

Wiring diagrams are also provided in Figures 20 and 21 on the next page.

There is a fourth lead on one end of the shielded cable. This is a ground lead which is attached to the black wire of the cable. The ground lead should be connected to the terminal block inside the motor compartment.

Current PS360-series ovens have the shielded cable installed at the factory and do not require this retrofit.