Aside from the suggestions of others, there are a couple of more things that
I'd check:
Rock the band switches carefully back and forth. I've seen worn/dirty contacts
cause a sudden loss of transmit drive.
Also, check the SWR bridge diodes in the output network. They are the sensing
devices for the the ALC circuity. If one has shorted, output drive can drop to
zero.
Of course, if you have a 'scope, things become much easier. Simple follow the
signal from the mixer to the low level drive to the input of the final
amplifier.
I assume that receive is normal? That the external VFO jumper didn't fall from
the rear jacks?
73,
Doug/WA1TUT
>Subject: [TenTec] Omni C + new Ham = Oops.
>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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