[TenTec] Model 544 (or that era) part source needed

[Paul Christensen]

Found this message thread a bit late.  I am in the processes of localizing a
display brightness issue with my Triton 544 -- specifically the green
7-segment LED, manufactured by HP, part number 5082-7671.  The original
poster was looking for a replacement.  The LED is used to display the
Triton's 100 Hz digit.  My first thought was that the green LED required
replacement, but in thinking this though, I'm more inclined to believe it's
working correctly and that the driving circuitry requires further
investigating.  I cannot imagine ALL 7 segments loosing equal brightness
over time -- unless the LED driving current is at or near the absolute
current rating as shown on the HP datasheet.  

The HP 7-segment LED uses a common anode.  Two transistors, a PNP/NPN pair
are responsible for functioning as a switch and for regulating LED current.
I believe the 220K resistor from the LED driver chip is responsible for
setting LED display current.  In looking at the HP specs, achieving equal
luminance across the red and green light spectrum requires different LED
current.  However, Ten Tec used one resistor value (220K) for all red and
green LEDs.

In the next week or two, I plan on rebuilding the PTO.  I'll dig into the
brightness issue at that time and measure voltage across the LED segments
and compare with the HP data sheet.  The green segments should show voltage
about 0.3V more than red.  If they're equal, owing to the same 220K resistor
value, that will likely explain the slight brightness disparity.  Red LED
current should be about 1.8V versus 2.2V for the green LED.  The Plexiglas
display lens may also be contributing to some green spectrum attenuation.   

Paul, W9AC       
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Those LED displays date back to the 1970's, or maybe even a bit earlier.

The 54 used HP-5082 series LEDs for all counter sections... these 7 section
LED displays were .43"  (10.92mm) and common cathode, with right hand
decimal points.

The correct LED for the green display is a HP 5082-7671.  You could
substitute a red display--HP 5082-7651, or a  yellow display, HP 5082-7661.
  The red displays are extremely common and show up on eBay.  The green and
yellow displays are tad more uncommon, but this should still be a 1 to 5
dollar part on the surplus market since zillions were made.

regards

Pete  k1zjh