Might there be a short on the output of U1 pin 5? This is a TX output
from the driver chip, and even with the negative supply being low, it
should not be that close to zero, especially with the input at the
high rail. I would suggest looking for a short across C3, L2 to
ground, or even from U1 pin 5 to ground.
L2 may be suspect after you find the short, but it normally fails
open, which means the connector side is probably OK. It is also
possible that U1 is problematic, but I would look for the short
first. When you correct the short, the negative supply should return
to a more reasonable value since it will have a smaller load to drive.
On Nov 9, 2005, at 8:29 AM, Gilbert J Cross wrote:
Hi fellows. Can't manage to communicate between computer
and K2.
Through control program or HyperTerminal verified that serial port is
functional on the computer ( Win XP ).
Can hear Q1s signal loud.
Here are some voltage measurements made this morning.
U1-1 14.12 shud be 14
U1-2 -1.3mv " .1
U1-3 13.65 " 14
U1-4 -5.4mv " .1
U1-5 -.017mv " -8
U1-6 -2.38 " .1
U1-7 13.66 " 14
U1-8 -3.13 " -9
U1-9 0 " 0
U1-10 0 " 0
U1-11 4.89 " 5
U1-12 4.98 " 5
U1-13 4.89 " 4.5
U1-14 0 " 0
U1-15 4.89 " 4.5
U1-16 4.89 " 5
Wonder if getting voltage on pin 8 would to proper level would
cure the problem?
J1-1 0 shud be 0
2 -.011 " -8
3 -2.36 " .1
4 6.27 " 4.5
5 0 " 0
6 5.62 " 5.5
7 0 " 0
8 14.12 " 14
9 8.18 " 8
Voltages on J2 are in limits.
Any help would be greatly appreciated.
Thanks Gil K8EAG
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