Chasing the schematics, I find the meter is driven by the S-meter
circuits for SSB and FM through diodes for all positions of the meter
switch. The difference is that its also driven by a op amp on the 9 MHz
Mixer/IF board 81594 with a series cal pot and a diode. There's also a
shunt capacitor. If the cal pot got turned way up it might take over, if
the op amp failed or a board ground failed, or something failed in the
ALC FWD detector circuit to push lots of voltage to the op amp (U1A)
that would drive the meter full scale and beyond all the time. I didn't
chase down the FWD power detector circuit, but I think its also used for
ALC and I recall reports of Tentecs sometimes losing diodes in that
circuit from nearby lightning while connected to an antenna.
73, Jerry, K0CQ
On 1/25/2011 11:22 PM, Hamdriver66@aol.com wrote:
I have an Omni VI, upgrade one with all TenTec filters installed. The
S-meter has just developed a problem that I would like to ask for input to try
to solve.
The meter works as designed in all meter switch positions except for FWD,
where the needle pegs out at top of scale in receive or transmit, and stays
at full scale all the time.
I have reseated all the connectors and circuit boards that I can reach
without disassembling the whole radio and have used DeOxit on all switches and
controls.
Has anyone seen this condition and are there any ideas as to cause?
Thanks in advance for any help.
Mike K4KJC
|