Several weeks ago, someone on the list indicated that they could not rid
their Omni Six of audible "clicks" while listening with headphones. I
suggested removing plug 52 on the AF/IF Circuit board, but apparently, this
did not help.
After making yet another mod to my Omni Six last weekend, I noticed the same
problem for the first time: I was hearing audible clicks, to the point of
being annoying regardless of any front panel setting, including power and AF
loudness.
This weekend, I jumped in to find the cause. On my particular Omni Six,
several areas were contributing to the clicks. Through a combination of
regrounding, using shielded audio cable, and rerouting cables, I have my
Omni back to the point where no or clicks thumps are heard whatsoever. The
following steps may be of help to those who wish to minimize clicks in their
Omnis:
1) I'm a firm believer in removing plug 52 from the IF/AF circuit board.
Pull it, and tie-wrap it out of harms way.
2) Ground the heatsink tab of U8, the audio power amplifier. By pushing U8
against the side chassis, a hole can be drilled for placement of a #4 screw
which now grounds and heat-sinks U8 to the chassis.
3) Many audio cables use ribbon cable. I replaced several of these with
single-pair shielded cable to the AF pot, FIXED AUDIO Plug 57, and cut two
audio circuit traces on the AF/IF Board that were running too close to other
witching circuitry.
4) Cut the nylon tie-wrap that holds the cable bundle along side the chassis
near U8, separate and twist the wires, finding the right combination that
minimizes the clicks.
>From a schematic perspective, turning the AF control fully
counter-clockwise, should not produce any clicks, only absolute silence as
the pot's wiper arm becomes grounded. Only, the wires that run to the pot
are unshielded and the routing of the wires makes for a poor circuit ground.
-Paul, W9AC
--
FAQ on WWW: http://www.contesting.com/tentecfaq.htm
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|