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TS-930S METER BACK LIGHT REPLACEMENT

Replacement of the TS-930S meter backlight with new bright LEDs. 3 July 2018


The incandescent meter backlight(s) had failed and required replacement and while a simple like for like replacement was possible there was a much superior solution available with bright LED (Light Emitting Diodes) lamps. LEDs while having many superior characteristic when compared with traditional incandescent lamps, particularly when it comes to reliability are not always an ideal solution. A key performance difference that can make LED not ideal for display backlighting is that they radiate the light forward in a narrow beam of between 10 and 20 degrees as compared to the more omnidirectional pattern of most incandescent globes, therefore if the backlight as is often the case relies on a more omnidirectional light the replacement is not as straight forward as simply replacing the existing incandescent globes with the newer LED light. Fortunately the TS-930 radio is well suited to LED back lights for the meter and in fact the 5mm LED is almost a perfect physical fit; that said the two LEDs required for this job produced two intense spots in the dial. This problem was solved by scuffing the LED lens with fine sandpaper to create more light diffusion and the value of the LED current limiting resistor was significantly increased to reduce the LED brightness. See below photo.

 

Photo:  TS-930S with new bright blue LED meter back lights installed.

The TS-930 radioís dial light is powered by a 28V DC supply and it was found that two 1.8k (3.6k) ohm 0.5 Watt resistors in series with each of the 5mm Blue, 23500mcd LED gave a good results, however a bit more resistance may prove to give a slightly better result and is of cause subject to personal tastes.    

LED details

Size (mm): 5

Colour: Blue

Lens: Waterclear

Viewing Angle (Degrees): 15

Wavelength (nm): 470

IF Max Continuous (mA): 30

VF Typical (V): 3.2

IV Typical (mcd): 23500

 

Current limiting resistor calculation.

The below current limiting resistor calculation is to achieve the LEDís maximum performance which is based on an average life span for the LED however it is prudent to sacrifice brightness for extended reliability and the resistance value should be at least doubled or more. 

As in the fitting of this LED with the TS-930 radio it was determined that a 3.6k resistor for this particular LED was more than sufficient.

 

 

Video of the replacement of the TS-930S meter backlight with new bright LEDs

 

 

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Page last revised 15 August, 2018
 

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