Club 80-90 Forums

Hi all,

Dashboard diodes, anyone anything a bit more about them please?

Recently cleaned up all pcb contacts etc, then put everything back carefully, now oil pressure diode don't work Checked all circuit with meter and have volts/continuity and all's fine including the oil diode. As a test though, swaped with other red alternater diode - oil one then worked in the alternator contact (although flashed on/off like the indicator diode!,but proved it was ok?), but the alternator one then still didn't work in the oil one? Did make sure by way that the positive terminal was the right way round each time!

Do these x2 diodes have different values does anyone know? Any thoughts as ever always appreciated. Cheers.

they are all standard Light emmitting Diodes, and as long as you observe the polarity, will last for lots of years, so if you have one that wont work in more than one socket, change it for a known working one.....

LEDs can't have different "values". Simply speaking, they are a device which conducts in one direction only and emits light as it does so.

If you are getting a good contact on it then it should work. If it doesn't it's dead - although they don't easily "blow" like lamps, unless too much current flows through them (eg connecting them to too high a voltage without a protective resistor.

If you have a multimeter you can check a diode on the resistance setting - it should show a very high resistance in one direction and a low resistance (little more than zero) in the other.

asahartz wrote:If you have a multimeter you can check a diode on the resistance setting - it should show a very high resistance in one direction and a low resistance (little more than zero) in the other.

True, but some 'modern' multimeters don't have enough forward voltage to get an LED to conduct either way! Now, where's my AVO Mk 8...?

Being fair to modern meters though, they usually have a 'diode check' mode instead that will read the actual voltage drop for you.

..AVO Mk 8...?

- Ooh, now that brings back memories!

If you removed the led lamps, make sure you re-fitted them in the correct orientation .... LEDs only light up in one direction .. i.e. the two leads coming from them are + and - see below

[img:317:328]https://club8090.co.uk/wiki/images/Led_orientation.jpg[/img]
The longer lead is +ve but if the LED leads have been soldered in and trimmed you won;t know which is the right way so ...
You can't easily blow a LED if you get it connected in the wrong direction so just try both orientations.

Most, if not all LEDs have a flat side on the round base of them to denote which lead is the anode.

airhead wrote:Most, if not all LEDs have a flat side on the round base of them to denote which lead is the anode.

Erm... which is the cathode i think

short leg, flat spot and largest bit inside the led is cathode.

Titus A Duxass wrote:

..AVO Mk 8...?

- Ooh, now that brings back memories!

I think mine's still in the loft.

Titus A Duxass wrote:

..AVO Mk 8...?

- Ooh, now that brings back memories!

Yes .. for me too My Dad had one and I learned about electricity using it .. also built a crystal radio with an aerial as long as our back garden... Happy Days

The_blue wrote:

airhead wrote:Most, if not all LEDs have a flat side on the round base of them to denote which lead is the anode.

Erm... which is the cathode i think

short leg, flat spot and largest bit inside the led is cathode.

Mmmm, well its been a while since Ive soldered together a PCB!

Thanks everyone that'd replied to this one - think it got bit of a debate going there too!?

Will check it out again on the weekend when there's a bit more daylight about as well!.

Cheers all.