Lid Solenoid-J2-8 and J2-10 -approximately 97vdc.
(4) The T1 secondary has approximately 24 vac across its windings. CR1
rectifies the ac and C1 is the filter for the +18vdc supply regulated by CR3. F2 protects
T1 secondary. CR4 is a 12v zener diode which provides power for IC1, IC2, Q2, Q1
and K1. Z1 is a light emitting diode/transistor package. The positive +12v supply
forward biases Z1 turning it on and charging C3.
(5) The Q1 is on at this time because of the +12v supply and the voltage divider
network R10, R11 and R15. The collector of Q1 is low, and this low is felt to IC1 pin 2.
IC1 pin 3 is also low at this time, and there is no signal to the tachometer. The arm
attached to the armature motor turns as the armature turns. The arm will block the light
being emitted by Z1, turning off Z1. C3 discharges. This places a low on the base of
Q1, turning off Q1. A high will be felt from the collector of Q1 to IC1 pin 2.
(6) The high at IC1 pin 2 causes IC1 pin 3 to go high at this time. The high
at IC1 pin 3 is felt through R7, R8, R9, and the tachometer causing the tachometer to
read upscale. R9 is the tachometer adjust resistor. As the speed of the centrifuge
increases, IC1 pin 3 goes more positive causing the tachometer to read further upscale.
e. Lid Solenoid Circuit.
(1) The Q1, Q2, IC2, and K1 make up a circuit that de-energizes the lid solenoid
once the centrifuge drops below 50rpm. The same low felt on IC2 pin 2 is felt on the
base of Q1 when Z1 is not conducting and C3 is discharging. Whenever IC2 pin 2 goes
high, IC2 pin 3 goes high.
(2) This high energizes K1 coil. The K1's points are closed putting 120vac to
BR1. The output of BR1 will energize the lid solenoid so that the operator cannot open
the lid once 50rpm's have been reached.
(3) If the centrifuge times down or the speed control is set to zero, and the
centrifuge drops below 50rpm, the following happens. As the speed decreases, fewer
highs are felt to IC2 pin 2. Also at this time, the base of Q1 stays high longer, which
keeps Q1 on longer. This keeps Q2 off longer. When Q2 is off, C7 is allowed to
charge, putting a high on pins 6 and 7 of IC2. This high will cause IC2 3 to go low. K2
coil de-energizes and its points open. The 120vac is taken away from BR1. The lid solenoid
de-energizes, and the operator can open the lid on top of the centrifuge.
TROUBLESHOOTING FOR MALFUNCTIONS
You use a troubleshooting guide to isolate the cause of malfunctions. You first
identify the symptom, then check for the possible causes, and finally take the corrective
action. Refer to the troubleshooting guide in figure 2-2.