The TV TAB display unit is equipped with a keypad. The power button, function buttons and the brightness and contrast setting knobs are placed on the frontpanel module. The keypad module is connected to the frame by four allen head bolts. The electrical signals are connected by two 37 pin sub-d connectors.
The keypad module attatched to the TV TAB display unit.
The keypad module of the TB TAB display unit.
Unfortunately most of the buttons are marked with some unknown abbreviation. Here are the button markings with my guesses of the explanation:
WS = Wind shear/Warning System(s)/Weapons System(s)?
WPT = Waypoint?
FXPT = Fixed point?
TGT = Target?
LL = Low level?
ML = Medium level?
MKR = Marker?
NFX = ?
HTFX = HT fix?
FLW = Flight Warning?
PLN = Plan?
NAV = Navigation?
F/A = Fix/Attack (confirmed)
A-K = Letters A until K
L-V = Letters L until V
W-Z = Letters W until Z
ON = Power on button
TVM = TV (television) Missile (confirmed)
RCN = Reconnaissance?
FLR = Forward Looking Radar?
0-9 = Numbers 0 until 9
ENTER = Confirm entry
CONTRAST = Display contrast
BRT = Display brightness
The display module was in rather good shape. Based on other photos on the internet I guess this particular one is in a nice shape. But the device is rather dirty. There's dust in dirt in every corner and the front panel has ha film of dirt on it like shown below.
The front panel is rather dirty…
Based on experienced I know that the best results for cleaning is brushing pieces with water and some abrasive cleaning agent. A dish brush or toothbrush (for smaller parts) works great! Not removable parts or pars that don't withstand water can best be cleaned with some 70...100% isopropyl alcohol. After partial disassembly the front panel and buttons are scrubbed clean. The result is great. The buttons are clear white again and the worn gray paint is also gone. The buttons are made of clear plastic a white paint coating. The [TGT] button is probably mostly used since this is the most worn button. There are (as expected) no signs of damage of the cleaning.
The panle after cleaning. Spot the difference...
The dirty buttons before cleaning.
The buttons after cleaning.
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.
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.
other keyboard models
It turned out that there are more keyboard models. It's likely that the connections are the same so the modules are interchangeable. But the design is rather different. I guess the older design is shown below. It think this is the original design using bigger mechanical switches instead of pcb switches in the successor version. In the successor version are the holes for the mechanical switches still there. It's likely the electronics are changed and the aluminium body is not changed. In de older version are the buttons much more loose as visible below. And I guess there is no button illumination compared to the successor version. The older model is known as the V22.498.842 type where V22.498 indicates the TV TAB DU and the 842 indicates the keyboard unit. The old design has the type plate used on most if the modules. The old type module is made by Marconi Avionics and the newer models is made by STOP-CHOC LIMITEED as mentioned on the type plate. Also the power button is different. The newer model as a power button with a bulb for illumination of the power button and the button is removable from the outside without tools. It looks like the older version has a switch like the other buttons of the keyboard unit. I guess this is a clear sign of the development of the display units.
Older (original?) keyboard module.