(c)
There is a broken chair or sheared pin in the motor sprocket.
(d) There is a bent or broken lift control switch.
(e) There is a faulty motor or capacitor.
(f)
The automatic controls are not functioning.
(g) The automatic exit switch is in the wrong position.
(h) There is a faulty relay.
b. If your problem is that the manual control switch for lift fails to raise or lower
the chair, there are three probable causes from a list of all possible causes. See the
appendix.
(1) The chain could be broken. You test this by visually inspecting. If
broken, you replace it.
(2) The pin on the motor sprocket could be sheared. Test by visually
inspecting. If sheared, replace the motor. Refer to Lesson 3, Remove and Replace or
Repair Defective Components of the Dental Chair.
(3) You could have a faulty switch or wiring harness. Test by using the
following procedures.
(a) Remove the switch bezel from the chair.
(b) Use a voltmeter to check for a reading of 115v or 220v, as
applicable, between terminal 2 and the neutral line. If there is no reading, the wiring
harness is faulty. Replace the wiring harness.
(c) If there is a reading in (b) above, check for a reading of 115v or
220v as applicable between terminal 3 and the neutral line when you depress the top
side of the control switch and between terminal 1 and the neutral line when you depress
the bottom side of the switch. If there is no reading, the switch is faulty. Refer to
Lesson 3, Remove and Replace or Repair Defective Components of the Dental Chair.
(d) If there is a reading on both switch legs, the motor is faulty. Refer
to Lesson 3, Remove and Replace or Repair Defective Components of the Dental
Chair.
MD0373
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