AO NCT

Simple checks. Select the problem from the list below:

1. Unit not firing when button pressed
2. Lamp dim
3. Lift mechanism stiff
4. Safety lock mechanism
5. Calibration check
6. Changing NCT Bulb

1. UNIT NOT FIRING WHEN BUTTON PRESSED
PROBLEM: Unit switched on with display showing 65. When patient is correctly aligned and fire button pressed, instrument does not fire.

Check that fire switch is operating. When you press the fire switch, you should be able to hear a distinct click. If no click is audible, it may be that the pin is stuck down.. The fire pin can be pulled out of the hole in the middle of the UP/DOWN knob. The lower part of the pin is often covered in very sticky grease. Clean pin with some alcohol wipes and re-fit. If no better, call us for a service visit.

Switch instrument to demo mode by pressing D button. Wait 10 seconds and press fire button. Instrument should fire and display should read 50 +/- 1. If instrument does not fire and display stays on 65, call us for service visit.

Switch instrument to override mode by pressing top button marked with concentric circles. Wait 10 seconds and press fire button. Instrument should fire more powerfully than normal and display should read 99. If instrument does not fire and display stays on 65, call us for service visit.

If the instrument fires on it's own when it is switched off, this signifies an electronic fault. Call us for a service visit.

2. LAMP DIM
If the lamp is as bright as it should be, you should quite easily be able to see a patch of light projected onto your finger if you hold it about 10mm in front of the puff tube. Make sure the forehead switch is activated to set the brightness of the bulb to maximum. The forehead pad on the patient's left has a built in switch which sets the brightness of the bulb to full power when depressed. This also has an override facility which allows it to be permanently set on by pulling back the knurled nut on the rear of the pad twisting it half a turn in either direction. If the forehead switch is pressed, the red LED on the top of the forehead bar should illuminate. Alternatively if the unit has a fixation device, the fixation bulb should increase in brightness.

PROBLEM: Bulb blackened. This is caused if the forehead switch override is left on for too long. This is usually signified by the red LED on the top of the forehead bar being permanently on. The bulb is designed to work on low brightness and should only be on high brightness when being used on a patient.

REMEDY: Change bulb and try to ensure override switch not left on. (see changing NCT bulb)

PROBLEM: Bulb incorrectly aligned. NCT bulbs must be correctly aligned and adjusted when fitted to optimise brightntess.

REMEDY: Align bulb. (see changing NCT bulb)

PROBLEM: Dirty puff tube.

The glass around the puff tube becomes very dirty with use because the air puff splashes moisture from the patients eye onto the glass. Clean the glass with a soft lens cleaning cloth. Periodically, it is a good idea to remove the tube and clean the glass on the inside of the puff tube and check that the tube is not blocked in any way. Also, clean the angled glass inside the puff tube chamber as you will usually find a small dirty patch where it lines up with the inside end of puff tube.

REMEDY: Remove the tube by gripping the knurled part of the assembly and turning anti-clockwise. Be very careful when handling this part as it is very delicate and very expensive.

LIFT MECHANISM STIFF
If the lift mechanism is difficult to turn, it is likely that the grease on the lift screw has dried out and become too sticky.

REMEDY: Turn the lift mechanism down to the bottom of it's travel and remove the lift knob. Firstly pull the firing button pin out of the middle of the lift knob. Then insert a 5/64" allen key into the hole in the side of the lift knob and loosen the allen grub screw a couple of turns. Removing the knob will reveal the lift screw which can be seen through the hole in the top of the chassis. Squirt some WD40 or other penetrating oil onto the screw and work the mechanism up and down. For proper operation, you should be able to turn the mechanism with the top of the screw with your fingers.

Before re-fitting the lift knob, check the underside of it and make sure there are no cracks in the circular ring where the grub screw fits. If there are any cracks, the knob will become loose and stop functioning. Note that the top of the screw mechanism is a D shape to locate the grub screw. Re-fit the knob and tighten the grub screw but do not over tighten as this part of the knob is easily cracked.

SAFETY LOCK MECHANISM
Check the operation of the safety lock mechanism regularly. Pull the head of the instrument all the way back by the joystick and lift the safety lock release knob on the left of the instrument. The lock should prevent the head from being pushed forward more than about half way. If the mechanism does not work, you may find that the rack has come out of it's guide and is swinging loosly out of the mechanism. If this is so, call for a service visit.

CALIBRATION CHECK
The NCT has a basic calibration check which should be performed regularly. Switch the instrument on and press the demo mode button. Wait 10 seconds and press the fire button. The instrument should fire and the display should read 50 +/- 1.

Even if this is correct, it does not necessarily mean the calibration is accurate. If you suspect the calibration is incorrect because you have a higher than expected number of patients with high or low readings, we have the test eyes to check the calibration.

CHANGING THE NCT BULB
Using a 3/32" allen key, undo the 2 screws securing the lid and remove it. Looking into the top of the instrument from the user side, the bulb can be located in the left corner nearest to the eyepiece. It has 2 usually white wires going to it and the mounting is usually marked with the letter B. You will also notice the holder has a series of rings engraved on it. On the top of the mounting is a small grub screw. Loosen the grub screw with a 1/16" allen key and pull the holder out of the mounting. Undo the knurled nut around the bulb and remove the bulb from the holder. Remove the knurled nut from the bulb. THE BULB DOES NOT COME WITH THE KNURLED NUT SO IT MUST BE REMOVED.

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