Testing Classic series LEDs ??

I want to be able to test the five digit LED packs that are used in the classic series. Can anyone tell me what the pinouts are for these, and what a suitable test voltage would be. - Thanks, John


Since they are red LEDs, their forward voltage will be 1.6 volt when lit. The maximum reverse voltage should be about 3 V. The maximum steady current should be about 15 or 20 mA, but you may play on the safe side with some 10 mA.

So, two alkaline batteries in series will give 3 V, and with a 150 ohm series resistor you can build a probe you can use to test the different pins rather safely. You should find 8 anodes (the pins where the positive should be applied), and such anodes will correspond to the seven segments and the decimal point. There will be five cathodes (negative lead), one for each of the digits position.
Please work carefully, I can not warranty any results; but it should be simple if you are electronics inclined.


Actually, if you use a DMM in the Diode setting, you'll not only be able to safely measure the forward bias, you'll actually see the segments faintly light up as you do. I think this is probably the safest testing method.



I do agree. a DMM is a good and safe way to test LED displays.


Thanks guys, I actually did it with 3V and a 150ohm resistor. Seems to work quite well. The only problem is I found segments not working, so can anyone help with replacements ?. I heard a story (probably heard it here), that HP had a newer display 5082-7405 that will work. Anyone had any experience with this ? Any idea where I'd get some ? Thanks, John


From Alex Knight's page on the Classic series LEDs:

"In mid-1997, Arrow Electronics, a major components distributor, still had a supply of the HP# 5082-7405 LED modules, at a price of approx. $25.00 U.S. each.

"That's the good news. The bad news is that there is a significant variation on the brightness of different lots of the LED modules, and each module is marked on the bottom with a letter indicating the relative brightness.

"Some modules I obtained that had a date code of late 1996 were marked with the letter "W" and were significantly brighter than the modules I had pulled from a 1973-vintage machine that had modules marked "J", which were themselves slightly brighter than modules marked "H" from a 1975- vintage machine.

"Therefore, if you decide to have a module replaced, you will likely either have to live with having a group of 5 digits at a different brightness, or to buy three brand new modules at a cost of about $75.00."

(AKKnight, w/Joe Rigdon)


Does anyone know if that's the same Arrow Electronics at www.arrow.com ??


Yeh, that's the one... an electronics distributor, been around for quite a while. At quantities below 100, they aren't cheap.

You might do a search out on the web... sometimes companies have excess inventories of parts like that... maybe they built all their piglet-counters and had three displays left over... and a company with excess inventory will often sell you what they have at a decent price, because their accountants hate to count them as taxable inventory.

Possibly Related Threads...
Thread Author Replies Views Last Post
  A Wonderful Classic HP Calculator BShoring 2 1,067 11-22-2013, 05:25 PM
Last Post: BShoring
  Classic battery polarity Kiyoshi Akima 2 1,227 11-08-2013, 01:31 AM
Last Post: Kiyoshi Akima
  CLASSIC/SPICE KEY LEGENDS Mike T. 2 1,098 08-21-2013, 04:53 PM
Last Post: Mike T.
  Woodstock, Classic & Spices for iPhone Matt Agajanian 8 2,211 07-10-2013, 06:10 PM
Last Post: BShoring
  Testing card reader motor for 65 Michae Altmann 2 1,227 03-17-2013, 09:24 PM
Last Post: Randy
  Classic calculator display chip type number? Juergen Hofstaedter 3 1,220 01-22-2013, 12:47 PM
Last Post: Eric Smith
  [WP 34S] New GCC - Testing required Marcus von Cube, Germany 3 1,155 01-07-2013, 01:59 PM
Last Post: Marcus von Cube, Germany
  Classic Series Enter Key Dan Lewis 15 3,217 12-19-2012, 09:10 AM
Last Post: Thomas Radtke
  Testing the water Ken McPherson 0 674 08-07-2012, 09:18 PM
Last Post: Ken McPherson
  Classic (HP-67) charger issues revisited Matt Agajanian 6 1,814 05-20-2012, 10:50 PM
Last Post: Matt Agajanian

Forum Jump: