The readout on the Omni 6 can be straightened out by measuring the voltage
at the test point just off of the signal charge pump transistors on the
Logic Board schematic.
The voltage test point is just below the ADSP 2105 chip on the schematic.
Q's 3,4,5, and 6 are the signal charge pump. By adjusting the inductors as
you switch thru the bands, on the L.O. mixer board, and adusting the output
to 2volts, at that test point, you have brought the phase locked loop and
the crystal subband locking systems into its designed synch, hence an
accurate readout. Now this procedure can be pretty confusing if you tweak
the wrong inductor for a given band, you must begin over again. Care must be
taken because the inductors are not ascending in the lineup. If you measure
2volts plus or minus 1 volt, there is no need to adjust the inductor on the
L.O. board for that band. If the readout is still off, or if the voltage
skips around on a particular band, then suspect that the crystal has
migrated/aged out of tolerance and must be replaced. A little coolant to
that crystal will tell the tale. My shchematic says 2v right next to r13 on
the 81606 circuit board which is the Logic Board.
Moreover, if you dont understand the above procedure, dont do it. I will not
be responsible for any calamitous results if for some reason you interpret
the above as a go ahead to tweak every thing and or the wrong thing. The
voltages are not dc volts and no amount of hoping your vom will read
correctly will make it so.
My friend who has lab quality test equipment did this procedure and found
faulty crystals and a failed chip. Both times the above procedure was done
at the end and my Omni has been accurate to 2-3 hertz for the last year or
so. I had noticed that my problems began with the readout being 50 hertz
off, and then worsening with time.
My radio is 1995 vintage and before I bought it, two previous owners sent it
in for a thorough going over. So over time as use shakes out the weak
components, its nice to know that not very much can go wrong if you keep up
with the problems. Ive owned it since Nov. 2000.
|