24 Jul
2012
24 Jul
'12
11:47 a.m.
Hi Andrew,
On Tue, Jul 24, 2012 at 4:26 AM, Andrew Quinn <jaquinn2001 at gmail.com> wrote:
Correction to that.... it should read:
The 7417 needs to pull this to ground to get the display segments to switch off.
So what I am seeing is the line coming in to the front panel from the
control board is pulled to ground and does not change.
So it could be:
1. The pullup resistor on the front panel board has failed.
2. The 7417 on the controller board has failed and is pulling the
line to ground.
3. Something feeding the 7417 on the controller board has failed.
Number 2 is a very common mode of failure for open-collector 7400's
like the 7417. My money's still on that one. Time to desolder it and
put in a new one.
Camiel.