LED - troubleshooting why they do not work

[chlowden]

Hello
I have what I presume is a simple question concerning how LEDs work.
I have 3 LED looking light sources that are set in concrete. The "LEDs" were set into concrete about 30 years and worked for sometime. Recently, I wanted to get them working again and they do not. I checked the 2 wires of the LEDs with my volt meter and it read that there was a 38 volt DC supply. The LEDs are being supplied by a PCB of a hifi amplifier which seems to run at 38 volts from the readings I took on other parts of the PCB.
Firstly, I can't find anything very pertinent on LEDs at 38 volts. I know of LEDs at 3 volts.
Therefore, my question is what sort of LEDs could I being dealing with? What would be the best way to confirm that they are broken?
Thank you

 

[Tha fios agaibh]

What would be the best way to confirm that they are broken?
Thank you

The "LEDs" were set into concrete about 30 years.

 

[Alec_t]

Welcome to EP!
If a LED light has been working with a 38V supply then it probably consists of several LEDs in series. As you say, a common LED (white type) has a Vfwd of about 3V, so there could be 10 or more in a series string.
If the LEDs are set in concrete outside the house the most likely failure cause would be corrosion of conductors/joints/connectors.

 

[chlowden]

It is a "concrete stereo"
http://collections.vam.ac.uk/item/O1227026/concrete-stereo-stereo-system-arad-ron/
There are only 3 leds are in the concrete casing. Inside is a ROTEL amp that has been adapted for the concrete casing and the LEDs are fed by the amp PCB.

 

[shrtrnd]

I hope the Moderators bookmark this one.
You wouldn't happen to be the artist, would you?

 

[chlowden]

I hope the Moderators bookmark this one.
You wouldn't happen to be the artist, would you?

The artist who built it has since become a famous designer since i bough the system in 1985.
http://www.ronarad.co.uk/
. Inside it is very rudimentary but I did not buy it for its sound. It just looks so cool. that said, the sound is far better than you can image.

 

[davenn]

What would be the best way to confirm that they are broken?

not working with appropriate voltage across them would be the obvious indication
reason for the failure is most likely the minerals etc in the concrete having corroded the leads to the LED's

 

[chlowden]

I had not thought about corrosion. Thanks for sharing it.