Question on airplane indicators. - Page 1
Forum section: electronics / beginners

author: Electrolitty
author_rank: Contributor
timestamp: May 13, 2023, 11:16:16 am
content: I got a bunch of old (but unused) electronic parts and among these are a few indicators or dashboard lights probably used in airplanes.I tried to find a datasheet but I couldn't find any specifications about them.Maybe a forum member knows better where to search.Exact inscriptions on the component are as follows.ALLARD AVIONICS108-88 28 VDC716835-1D/C 8839I include a picture but it's not possible to show all of the labeling.On the bottom, it has got three pins. Resistance between pin 1 and 2 is about 650Ω, same between pin 2 and 3. Between pin 1 and 3 it is 1300Ω. Randomly applying 28V to the pins doesn't show any result.Thanks for any help with this.

author: m k
author_rank: Super Contributor
timestamp: May 19, 2023, 12:37:40 pm
content: Maybe all 3 must be connected.

author: CaptDon
author_rank: Super Contributor
timestamp: May 19, 2023, 01:03:21 pm
content: I took a resistance measurement on incandescent gain-of-wheat bulbs designed for 28 volts. None were over 100 ohms. Your reading of 600+ ohms would be a current of around 40 milliamps which would be on the high side for older LED's but practical for an aircraft indicator with a specified lifetime. It occurs to me that your indicator was some sort of dual readout such as 'APU' in the lower half and 'ON' in the upper half and was illuminated by LED's. It seems possible either the LED's are dead or were damaged by reverse voltage connections (older LED's didn't like reverse voltage and especially high reverse voltage like 28vdc). Or they were manufacturer defects that someone got a hold of and decided to profit from it. That is one of the reasons manufacturers often crush and destroy components that don't meet specs! Back in the day of vacuum tubes being very common General Electric crushed all that didn't meet specs. Sadly many 'second rate' tubes from several manufacturers 'went out the back door' and got sold under suspect brand names. Often you could buy a 'new' tube that was in worse condition than the used one you were replacing!!Cheers!!

author: Electrolitty
author_rank: Contributor
timestamp: May 19, 2023, 06:33:46 pm
content: I made a few more tests and I found out that it's not a LED nor a light bulb but simply an indicator that switches toredwhen connecting middle and right pin (as shown on the picture above) and switching toblackwhen connected to middle and left pin, the middle pin always being the negative one.No idea where this is used as it does not seem to have background illumination.Thanks for your help.

author: sokoloff
author_rank: Super Contributor
timestamp: May 19, 2023, 06:42:59 pm
content: Could it be side illuminated when installed? Is the side of it translucent?

author: Electrolitty
author_rank: Contributor
timestamp: May 19, 2023, 07:03:16 pm
content: Quote from: sokoloff on May 19, 2023, 06:42:59 pmYes, that may well be. The acrylic glas cover (about 2mm thick) could possibly be side illuminated. On the top a black border around the indicator enhances visibility (picture at the top).

author: floobydust
author_rank: Super Contributor
timestamp: May 19, 2023, 09:18:44 pm
content: I found some data asFault Locating Indicator NSN 6625-01-159-3828but made by Ratheon or Applied Magnetics."An electrically activated item specifically designed to indicate the occurrence of a malfunction in a component of an electronic set, central or system. it may indicate the malfunction by a pop-out button (e.g. ground fault interrupt outlets) or color change by emitted light or displayed in a window. The indicator may utilize a "push to test" button. It does not make quantitative or qualitative tests such a provided by test sets."

author: EPAIII
author_rank: Super Contributor
timestamp: May 20, 2023, 04:46:23 am
content: You say you have a bunch. A few minutes of quality time with a Dremel tool, an abrasive cutting wheel, some eye protection, and one sacrificial example may tell the whole story.Don't neglect the eye protection.

author: Electrolitty
author_rank: Contributor
timestamp: May 20, 2023, 09:33:17 am
content: Quote from: floobydust on May 19, 2023, 09:18:44 pmYes, these seem to be comparable parts. The company "Allard Aviation" that manufactured mine originally doesn't seem to exist anymore.@EPAIII: I've got only four pieces, destroying one is not an option for me.