Actually, I think essentially 0V at pins 14 and 15 of the DAC is correct. Pin 14 is a
current input, not a voltage one. Pin 5 of the 4560
should be at 2.0 volts DC, so check that. Probably it's fine.
T0 is used to sense the comparator output. When the comparator is high,
it should be at 5V. When the comparator is low, D9 clamps it at 0.6V below
ground, and D10 add 0.6V to that so you get 0V. Those are the two levels you
should see. The comparator is part of a feedback ADC. The DAC output is compared
with the front panel voltage being measured, and adjusted until its the same. At that pt,
the front panel voltage is known.
Bob
--------------------------------------------
On Sat, 7/2/16, noddyspuncture@... [PolySix] <PolySix@yahoogroups.com> wrote:
Subject: Re: [PolySix] Another P6 with all LED's lit....
To: PolySix@yahoogroups.com
Date: Saturday, July 2, 2016, 3:11 PM
As I have checked and quadruple checked all tracks,
traces and connections - and all are OK, I am assuming
it's component failure..!? I had been suspecting the
8048 but after confirming the reset function is working I am
hoping that it is some other component.
Vref + & - ... pins 14 & 15
of the A/D converter both read millivolts... I'm
thinking this might be a clue...?
By the way would anyone kn ow what I
should be seeing on TO... pin 1 of the 8048
...?
Cheers,Tom