panel illumination
During disassembly I saw a miniature BNC connector at the rear of the front panel. I couldn’t explain the function of the connection so I disassembled the front panel. At first I thought the wiring acts as a sort of antenna. But the wiring is parallel with some electronics around the brighter/contrast knob position. The milled pocket is also at both sides of the left/right switch. Then it occurred to me that the milled pocket matches the text at the front panel. Therefore is rather logic that the milled pockets are equipped with el-film lighting. The electroluminescence thin film acts as a light source for the text and markings of the front panel. The front panel is made of transparent plastic and coated with grey paint. By applying a (rather) high voltage to the el-film, the print panel markings are illuminated. Due to the high voltage and possible electromagnetic interference the wiring is shielded and a small BNC connector is used. The el-film is made water-resistant by applying some silicon like flexible substance.
Small BNC for el-film illumination power supply.
Opened frontpanel assembly.
El-film illumination placed in the milled out front panel pockets.
An animation of the first illumination test.
button illumination
All the buttons are also illuminated. The button holder and buttons are made of transparent plastic and coated grey or white. The printed circuit board is equipped with cylindrical light sources. Led lights would be logical nowadays, but since there’s a blue(ish) plastic around the light sources a filament bulb is likely. The red(ish) light from a bulb is compensated by the blu(ish) plastic creating white/greenish light. The light sources are marked “LP”, so a bulb lamp would indeed be logical. The light sources fit in the milled pockets of the button holder panel. The light is distributed via the plastic panel to the buttons. There are also black and white painted areas on the buttons and button holder panel. This is probably done for evenly spreading the light to each button. This process of painting was probably rather time consuming and required some experience…
Transparent buttons with (painted) pockets for evenly spreading the light.
Printed circuit board with light sources.
At a first test, the button illumination didn't work. Since is not likely all the lamps failed, I tested the voltage regulator and the bulbs separately. The bulbs illuminate when power is applied, so the bulbs work fine. I guessed the voltages and at 10 VDC the current draw was already 1,22 Amps! For now I want to keep the device original, but replacing the bulbs with light emitting diodes (leds) is a serious option to consider to reduce the power consumption significantly. The power to the keypad unit is regulated and fed to the bulbs. Since the input voltage is 28 VDC and the likely voltage approximately 10 VDC/1,22 Amps, a lot of power is converted to heat. 28 VDC of imput voltage minus 10 VCD of desired voltage results in 18 VDC of voltage drop. 18 VDC * 1,22 A = 22 Watts! It's likely the voltage regulator failed due to the wear of high dissipation. The regulator is fitted in the keyboard module and probably can't get rid of all the heat like it should. Replacing the bulbs by leds is probably a wise idea to get the device more stable and the power consumption would be much less.
Button illumination test.
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3. assemblies
WS = Wind shear/Warning System(s)/Weapons System(s)?
