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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 had failed and required replacement. While a simple like-for-like replacement was possible, there was a much superior solution available with bright LED (Light Emitting Diodes) lamps. LEDs, with their many superior characteristics compared to traditional incandescent lamps, particularly in terms of reliability, are not always ideal. One key performance difference that can make LEDs less suitable for display backlighting is their forward radiation of light in a narrow beam of between 10 and 20 degrees, 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 straightforward as simply replacing the existing incandescent globes with the newer LED lights. Fortunately, the TS-930 radio is well suited for LED backlighting for the meter, and in fact, the 5mm LED is almost a perfect physical fit. That being said, the two LEDs required for this job produced two intense spots on 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 radio's dial light is powered by a 28V DC supply. It was found that using two 1.8k (3.6k) ohm 0.5 Watt resistors in series with each of the 5mm Blue, 23500mcd LED gave good results. However, adding a bit more resistance may potentially provide a slightly better result, which, of course, is subject to personal preference.  

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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