Peter Miles
Northam, Western Australia QRZ Page: VK6YSF
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Media
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 LED’s
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