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Testing Classic series LEDs ?? - Printable Version

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Testing Classic series LEDs ?? - John Robinson - 08-16-2000

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

Re: Testing Classic series LEDs ?? - Andrés C. Rodríguez (Argentina) - 08-16-2000

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.

Re: Testing Classic series LEDs ?? - Viktor Toth - 08-17-2000

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.


Re: Testing Classic series LEDs ?? - Andrés C. Rodríguez (Argentina) - 08-17-2000

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

Re: Testing Classic series LEDs ?? - John Robinson - 08-17-2000

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

Re: Testing Classic series LEDs ?? - Glynn - 08-17-2000

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)

Re: Testing Classic series LEDs ?? - John Robinson - 08-18-2000

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

Re: Testing Classic series LEDs ?? - Glynn - 08-18-2000

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.