At 01:27 PM 04/08/06, you wrote:
>
>Our club 220 machine has been giving a lot of trouble with the squelch.
>
>The problem is that the squelch works fine for a while, then quits.
>By that I mean that it will not squelch even with no input signal at
>all.  No real clues, and the schematic is not very helpful.
>
>Any ideas?

Don't forget that a squelch circuit mutes when the squelch
noise is at maximum.  Depending on the circuit design (I'm
not familiar with the Maggot squelch circuit) the squelch pot
either feeds a varying DC voltage or a variable AC voltage to
a comparator circuit. The  comparator output goes active
(either high or low depends on the circuit design) to mute
the audio gate / audio mute circuit. This can get confusing
if you get into the "mindthink mode" that audio off is circuit
off - it's not!

Any change in the level going into the squelch pot or coming
from it will cause the comparator to see less noise and open
the audio gate.

BTW I have fixed more squelch problems with two tricks:
One, any connector in the path from discriminator audio
to squelch pot to audio mute circuit is suspect. Any drop
in level is interpreted by the squelch circuit as the presence
of a quieting signal. Wiggling the connectors is a quick
test.
Two, many squelch pots are not sealed and a squirt of
cleaner into the squelch pot followed by a few twists of
the knob can work wonders....

And several years ago I found a bad spot in a hilltop repeater
squelch pot and did a quick fix by swapping the wiring on
the two fixed ends so that the threshold spot moved to a
undamaged area of the pot.  So what that the pot now twists
backwards? How often do you adjust the repeater squelch
anyway?

And later on we wired in an EEPOT chip and programmed
the controller with three macros: they selected one of three
"settings" ... loose, normal and tight.  We had problems
with the setting being "remembered" through a power fail
until we programmed the controller to zero the pot and
count up to the new setting on any change.  It helps
when it's a controller that you have the source code to...

So my suggestion is to put a voltmeter (either AC or DC,
depending on the circuitry)  on the wiper of the squelch
pot. See what it reads normally and when the squelch
is blowing.  That will be a first step in diagnosis.

Mike WA6ILQ





 
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