Or... cold solder joint. Check it. Just re-solder all the connections.
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Dr. Gerald N. Johnson
Sent: Thursday, May 27, 2010 5:11 PM
To: Dave Plews
Cc: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Omni C (Model 546C) front end...
RF coils don't go bad often, and then its one of the causes I mentioned,
lightning or transmit power and then it usually shows up with smoke
residue in the vicinity. I nearly always expect the transistor to be
fried first. Though sitting a long time a bit of residual solder flux
might have corroded through a fine coil wire.
Low mixer injection level will also kill sensitivity.
Its illogical for a coil that is used on all bands to cause poor
sensitivity just on the low bands. I think 160 through 30 all use high
side injection to make LSB be the sideband #1. I'd look there. Check the
trap, if its not working right it could drop sensitivity. E.g. trimmer
capacitor not making contact. Ditto tuning capacitors that are on the
switch wafer external to the front end board, their grounding and the
board grounding. You can check the coil for opens with an ohmmeter, you
can't check it for shorted turns with the ohmmeter, you need a q-meter
and information on what the coil Q should have been. And the coil out of
the circuit, though a grid dipper would hint at coil Q in the circuit.
It should be resonant on each band. But with it shielded you can't use a
grid dipper on it. Being in the shield make the mouse activity of
chewing difficult. Leaving corrosive liquids that could trickle inside
the shield is possible.
73, Jerry, K0CQ
On 5/27/2010 4:23 PM, Dave Plews wrote:
> Hi Jerry, I'm not sure what happened to it. It's been dormant for a long
> time and I took it out of storage. Played with it a bit and noted that
the
> sensitivity wasn't nearly as good as it should especially on 10 Mhz. A
few
> weeks went by and the digital readouts started acting up. The receiver
> worked fine by lost the frequency LEDs as I recall on 7 Mhz, 14 Mhz and I
> think 28 Mhz. The PTO needed a rebuild, too. So I decided to have Ten
Tec
> repair take a look at it. They identified the sensitivity issue relating
to
> the L1 coil on the RF amp board.
> Now the sensitivity is bad on 160 - 30 meters. It seems to play okay on
the
> high frequencies. I just wanted to get it working as a back rig for Field
> Day if I could. As the problems became many I decided to take the leap.
I
> think I've leaped too far.
> If someone had an Omni D parts rig, perhaps the RF amp board could be used
> in mine to have at least one good radio.
> 73, Dave...
>
>
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