I agree with Jim on this.
Yes, all 5 of my supplies, switchers and linear ones, have had grounding
issues mostly the result of PAINT! Be it paint where the 3rd pin ground
wire attached to the chassis, or the DC neg attached to the chassis or the
outer case not connected to the bottom case because of paint.
SOLUTION:
Just take the things apart, remove the screws, rivets or what ever holds
things together, sand the area around the hole until you see bright metal
and then put it all back together. I personally prefer using screws and
internal tooth lock washers for re-assembly.
73
Bob, K4TAX
----- Original Message -----
From: "Jim Brown" <k9yc@audiosystemsgroup.com>
To: <tentec@contesting.com>
Sent: Wednesday, September 17, 2014 11:17 AM
Subject: Re: [TenTec] TT 940 Power Supply
On Wed,9/17/2014 9:02 AM, denton sprague wrote:
an update…..I strapped my Omni 7's ground to the negative line to my
Astron 30 amp switching supply….I also installed two ferrite clamp on
chokes on the dc lines on the inside of the power supply.
Something else to look at in the Astron. I've never seen an Astron
switcher, but I've had a bunch of Astron linear supplies over the years,
and every one I've opened up was built with a bonding failure.
Specifically, the green wire from the AC cord goes to the mounting lug
of a terminal strip. The negative side of DC is also tied to this point.
BUT -- the terminal strip is insulated from the chassis by paint. This
would cause RFI to the regulator in a linear Astron, and would cause an
Astron switching power supply to radiate noise on both the power cable
and the DC cable.
An easy test for this -- disconnect the DC output cable and measure from
the power cable green wire (the round pin) to the chassis. You should
see a few tenths of an ohm for the length of the power cord. If you
don't, you've got that bonding problem.
The fix is easy -- just remove the screw, scrape the paint, and reinstall.
One of my linear Astrons had an additional shielding failure -- the two
pieces of the chassis failed to make contact because there was paint
between them. Same solution -- scrape the paint along the junctions.
73, Jim K9YC
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