Dicon LD-400

The Dicon field screener differs fundamentally from other makes of field screener as it has a moving fixation point and a smaller number of target LEDs. The logic behind this system is that the patient has to concentrate harder on following the red light and it is therefore less likely that their gaze will wander.

At the start of the test, the blind spot is located and this point is tested at various times during the test. If the patient sees the blind spot point, the instrument says the message "follow the red light".

An important thing to consider with the Dicon is that the computer program which operates the instrument is held on a floppy disc which is prone to malfunction. Each instrument has it's own serial numbered disc which contains calibration files specific to that particular instrument. You must not use the instrument with any disc other than the one supplied. In the case of the disc becoming faulty, you will have to obtain a new disc from the Dicon supplier specifying the serial number of your instrument and this costs around £78.00.

For this reason, it is a good idea to make a back up copy of the program disc. As it is a bootable disc, it is not possible to make a copy of the disc by copying it to a file on your PC and then copying it back to another disc. It will not work.

To make a copy disc, you will need a PC with a DOS based system i.e. Windows 95, Windows 98 or Windows ME with a floppy drive. Start the PC and go to the DOS editor and use the following code.

Diskcopy a: b:
You will be asked to insert the source disk into the A drive and hit return. You will then be asked to remove the source disc and insert the target disc and hit return. Make sure the disc you are copying onto is not set to write protect.

Start Up Sequence
When the instrument is switched on, the background illumination light comes on fully for a couple of seconds and usually, 2 or 3 of the green leds inside the screen light up. On the back of the instrument, next to where the mains lead plugs in, there are 2 LEDs, one green and one yellow. The green one should light up and the yellow one should not light up.

Then, the computer starts to boot, the background illumination sets to it's normal level, the green LEDs switch off and the red fixation light illuminates. This should be in the centre of the screen.

After this, the floppy drive starts to read the disc. The green light on the floppy disc driver illuminates and you should be able to hear the disc being read.

When the program has loaded, the motors are run to check the home sensors and then move the fixation to the centre of the screen. Then the background illumination is set.

The target LEDs are illuminated in increasing square and diamond shapes and this pattern is repeated on the display.

When the instrument has finished starting up, the display should read DM.

COMMON FAULTS

Main Switch
Main switch does not move correctly. It is quite common for the main switch to be jammed in the "on" position so that it cannot be turned off. This usually does not cause a malfunction as the instrument can be switched off at the socket. Sometimes a faulty main switch causes the fuses to blow and total loss of power.

In this case, call us for a service visit to replace or repair the main switch.

Power Supply
When the instrument is switched on, the Green LED on the rear of the instrument next to where the mains cable plugs in should be on. The yellow LED next to it should be off. If neither of the LEDs are illuminated, check the fuses in the input socket and the plug. IMPORTANT replace using only use the correct rated fuses.

If the fuses are discoloured or blow again immediately, there is probably a fault with one of the power supplies or the main switch. In this case, call us for a service visit.

If both the Green and the Yellow LEDs are illuminated, there is likely to be a fault with either of the power supply modules.

Disconnect the power connector which goes into the right hand socket at the bottom of the panel beneath the patient response button socket. If the yellow LED is still illuminated, the power supply will need replacement. If it goes off when disconnected from the main instrument, the fault may lie in the mechanism. In either case, call us for a service visit.

When switched on, background illumination stays on full and 2 or 3 LEDs light but nothing else happens.

This happens when the computer fails to start. This may be caused by a faulty power supply or a faulty motherboard. If the motherboard has failed, it is very difficult to locate replacements and may be expensive. Contact us for a service call.

When switched on, background illumination sets to lower level and central red LED is on but nothing else happens.

When this happens, it is usually because the program is not loading from the disc. This may be caused by a faulty power supply which has damaged the floppy driver or the program disc. (See notes on making a copy disc). Check to see if the green light is illuminating on the floppy driver. Also listen to the floppy driver. If the disc is loading correctly, there will be a kind of "ticking" noise from the floppy driver. If the disc spins continuously for about 3 seconds for 2 separate cycles, it is probably caused by a faulty program disc. Call us for a service visit.

H-S in Display
This is a Home Sensor error caused when the motors fail to set the home sensor. This is caused by either one of the power supplies being faulty or one of the motors being seized up. Listen to the motors during the start up. If the motor movement sounds very noisy or lumpy, the motor will need replacement. Call us for a service visit.

E Arrow Up in Display
Background light intensity is too high. Try turning off room lights or closing doors and curtains.

E Arrow Down in Display
Background light intensity is too low. Background illumination bulb may have failed or become dim in which case, contact us for a replacement. Sometimes the connector becomes faulty and you may need a service visit.

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