The 5 to 5.5 synthesizer will operate with no reference (out of lock, of
course).
The reference oscillator in an Omni VI is either on the CPU board or pendant
board on the chassis wall facing into the CPU area.
Radio will receive even if the reference is missing, it will only receive one
frequency, and will be very unstable. It will not transmit.
The way the radio works IS that the 5.0 to 5.5 synthesizer picks up the on the
20 MHz reference and locks.
The crystal oscillators for each band still operate with no reference, they
will just be off frequency. Thus you do not have a single crystal oscillator
problem. Each band has its own crystal oscillator that gets selected by the
data from the CPU.
If you are not getting band select data to the crystal oscillator board, look
at the serial to bus driver chip on the CPU board because that is where band
select originates.
I don't recall the chip number but it is right by the connector that connects
between the CPU and the rust all local oscillator board.
If your CPU were dead, the display would not change when you turn the main
tuning knob so it sounds like the CPU is OK.
my iPad
> On Jul 8, 2017, at 4:50 PM, Ken Brown <kenradiobrown@gmail.com> wrote:
>
> My Omni VI is dead, and it seems like it is because the band selecting
> crystal oscillator is not generating a signal.
>
> Voltmeter readings indicate that the board is getting the correct DC
> supplies , the +REG and +13.5v as well as the appropriate band select
> control voltages on connectors 82 and 83. Still I cannot detect a strong
> signal at the XTAL oscillator frequency for any band selected. This board
> is sort of hard to get to, and I would like to troubleshoot it on the bench
> and hopefully confirm it is working before I put it back in the radio.
>
> Since the fault is in the crystal oscillator, I think if I get that working
> I'll have it fixed. I don't think I need to supply the 5.0 to 5.5 MHz input
> to troubleshoot the crystal oscillator. I think if I give it DC supply
> voltages and band select voltage I ought to be able to get it to generate a
> signal when on the test bench. With nothing going to connector 84 the
> frequency will not be phase locked or precisely controlled but there should
> still be a strong oscillation very near the correct frequency for whichever
> band I connect the band select voltage to connector 82 or 83 for.
>
> I would like to hear from anyone who has tried this. Do I need to put a DC
> voltage on connector 84 to get it to work at all? Or should it oscillate
> with nothing connected to 84, and just be sort of free running at the
> crystal frequency with no correction voltage?
>
> Thanks, Ken N6KB
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