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

[Mike Bryce]

one thing to take into account is the fact there is a RED plastic filter in front of the LEDs, that’s going to cut the brightness of the green LED by a large degree. There’s probably nothing wrong with the display


Mike Bryce, WB8VGE
 the heathkit shop
SunLight energy systems
J e e p
o|||||||o






> On Dec 5, 2015, at 3:53 PM, Paul Christensen <w9ac at arrl.net> wrote:
> 
> 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       
> ----------------------------------------------------------------------------
> ----------------------------------------
> 
> 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
> 
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