19 Aug
2013
19 Aug
'13
4:56 p.m.
On Mon, 19 Aug 2013 21:03:24 +0100 (BST), ard at p850ug1.demon.co.uk (Tony Duell) wrote:
If that's 5V across the pins that conenct to the light source with the
later removed then fine, the voltmeter will not draw enocuh current ot
produce a significant drop across the series resistor.. If it's 5V with
the light source connected then I think said LED might well be
open-circuit.
All the rotary encoders on HP instruments from the late '70s thru the late '80s
used +5V, grain-of-wheat bulbs. I have yet to see a led used in any of the 15 - 20
encoders that I've repaired to date.
->CRC
As you have discovered these enocders do come apart. The light source is
an IR LED (so if you've put 5V striaght acorss it it's probably dead by
now!).
I did not -- I measured 5V across it when the keyboard was plugged in,
that's all.