[TenTec] Help - Omni V PA

[Paul]

Hi Tom.

Thanks for the tip!

I don't think that will be the problem, I haven't noticed any smell of
burning PCB.
I know what it smells like.. I used to repair TV / VCR stuff, and some of
the burnups in the TV sets were quite big and common.

If I have to check the PA for anything else I'll be sure to check the state
of the output transformer.

The problem also shows up when TX'ing into a dummy load, but even after 5
minutes I only smelled the usual hot heatsink etc smell.

Cheers!


Paul MW0CDO

----- Original Message ----- 
From: "Tom Althoff" <althoff at verizon.net>
To: <tentec at contesting.com>
Sent: Sunday, September 21, 2003 12:52 PM
Subject: Re: [TenTec] Help - Omni V PA


> Paul...if you operate key down into a dummy load on those frequencies does
> the rig still exhibit those symptoms?
>
> Try that and sniff  the top of the Omni near the heat sink (sounds odd, I
> know).
>
> If there is any smell like a burned resistor I may have a solution for you
> that requires a lot of disassembly and a little grinding of the pc board.
>
> My output transformer arced over between the 2 output transistors causing
> the phenolic (or is is fibreglass?) PC board material to char black and
> become conductive.   I ended up grinding away the PC board and creating an
> air gap between the to solder pads of the transformer...fixed my problem.
>
> My symptoms included burnt resistor smell,  flickering of ALC at key down
> and distortion of audio on transmit.  But yours sounds so frequency
specific
> that I doubt it's the same problem...like I said...just a shot in the dark
> in case you try everything else with no success.
>
> Tom K2TA
> Greenwood Lake, NY
>
> ----- Original Message ----- 
> From: "Paul" <gw7lhi at hotmail.com>
> To: "Ten-Tec List" <tentec at contesting.com>
> Sent: Saturday, September 13, 2003 5:29 PM
> Subject: [TenTec] Help - Omni V PA
>
>
> Hi.
>
> I have an OMNI V that I'm very happy with, apart from a minor issue on
20m.
>
> I've noticed that on 20m above 14.250, the PA appears to go unstable /
> parasitic.
>
> This results in poor audio reports from some contacts.
>
> I've tested into a dummy load, and in tune mode as I vary the carrier
power
> I notice a definite point where the PA ( or whatever ) suddenly starts to
> misbehave.
> This is visible on the ALC indicator, which dims slightly or begins to
> flicker even though the indicated RF output is not changing according to
the
> external metering / dummy load.
>
> The current drawn does not change significantly when this happens, it
stays
> right around 19 amps at 100w out.
>
> The effect is much more noticeable with an antenna connected.
> The antenna has a SWR of 1.2:1 and does not cause any problem to my FT-102
> or other solid state PA rigs.
>
> Any ideas?
>
> The problem only occurs on 20m between 14.250 approx and 14.350.
>
> The only clue I can offer is that the RF output is a little lower on 20m
> than any other band, but only by about 3-5 watts.
>
> The PSU is a home brew 30 amp hernia inducing beast, there is no issue
with
> it as the same effect is present with a fully charged car battery.
>
> I have also wired the DC power cable directly into the radio, as the molex
> (?) connector was causing approx 0.5v drop through it.
> I have also bypassed the fuse holder, no difference.
>
> Thanks for any input!
>
> Paul MW0CDO South Wales.
>
> PS: Does anyone know where I could get a set of keypad buttons suitable
for
> the V.9 upgrade?
> They appear to be like rocking horse fertiliser here in the UK...
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