You probably already did this, but check the coax jumper between the
transceiver and the tuner. I had a similar experience recently and it turned
out that a cold solder joint on a PL-259 was the culprit.
Jock - N1JI
Sent from my iPhone
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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