Mike and John,
Thanks for the replies.
John -- I'll take a look at the drivers -- I'd rather it be them, but we'll
see. I much appreciate the tuning tips. Being a newbie, I've yet to aquire
all the goodies like noise bridge / antenna analyzer, but I'll see if I can
borrow them from the local club.
Mike -- There is zero additional current on TX reflected by the ammeter
remaining at idle current. The AGC light does not light with DRIVE set max
in both LOCK mode and in SSB with microphone input.
Again, being a new ham I don't have a second radio to check for
transmission. I could rig an attenuating probe for my scope to check the
output directly, but all other signs say it is dead.
On to checking on the drivers... I was a bit surprised the power supply
didn't go overcurrent, since typical failure mode for output transistors is
to short. A driver failure would be a good possibility.
On Mon, Oct 14, 2013 at 6:45 PM, Mike Bryce <prosolar@sssnet.com> wrote:
> Don't jump to conclusions just because one is nearby.
>
> Are you pulling current on tx?
>
> If so how much?
>
> It's possible the low level driver went out.
>
> Can you hear yourself in another receiver?
>
> Mike wb8vge
>
>
> Sent from my iPad
>
> On Oct 14, 2013, at 5:28 PM, Paul Harker <paul.r.harker@gmail.com> wrote:
>
> > I am a new member of the amateur radio community, and my first HF rig is
> an
> > Omni C. I was attempting to tune an antenna with a MFJ949E, with the mode
> > select switch (SSB-R / SSB-N / CW / LOCK) switch in the LOCK position,
> and
> > DRIVE set just high enough to allow tuning.
> >
> > Suddenly the antenna tuner needles dropped to zero, and it appears I no
> > longer have RF output. The Model 255 power supply did not shut down, and
> > the receiver is still functioning. I am assuming that I managed to blow
> the
> > MRF458 output transistors due to doing _something_ wrong. Maybe just a
> > matter of fiddling too long and letting things get too hot. I don't know.
> >
> > Measuring the MRF458 with a meter suggests they might be bad, but it
> isn't
> > a case of a dead short, and in the past I've found that power transistors
> > can be deceiving when doing an in-circuit test.
> >
> > So... I looked for any sign of a fusible link or other protective circuit
> > in the Omni schematics and didn't see any, but I thought I'd ask the
> > experts before pressing "sumbit" on a transistor order.
> >
> > And any hints tips corrections to keep me from repeating my bungle would
> > also be appreciated.
> >
> > Much thanks,
> >
> > Paul
> > AC8OI
> > _______________________________________________
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> > TenTec@contesting.com
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> >
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