14 Jan
2015
14 Jan
'15
1:42 p.m.
Virtually all of the LED's on the front panel board had so much mouse pee
that the leads on the LEDS actually corroded through, so I need to replace
them all.
Without schematics, can anyone suggest how I might go about determining a
suitable replacement LED from an electrical perspective?
Long answer :
Trace out the circuit for one LED and its driver.
Most of the time such LEDs have a series resistor. The +ve side of the combination goes
to a supply line, the -ve side to the collector of a driver transistor, the emitter of
which is
grounded (this may be an open-collector gate like a 7406 or 7407). From that you can
estimate the voltage across the LED+resistor (= supply voltage - saturation voltage
of the driver transistor (say 0.5V)). Then the current through the thing is
(that voltage - forward voltage of LED)/series resistor. Substitute the forward voltage
of
some possible replacement LEDs and see if the current is sensible (compare to the
maximum current on that LED's data sheet).
Short answer :
Go and get some standard (not high brightness, high efficiency, or anything fancy
like that) red 0.2" (5mm, whatever) LEDs. Solder them in. I will bet it will work
fine.
-tony