[Racal] RA 6790/GM Problem

[Carcia, Francis A HS]

I had a similar problem with a RA6830 BFO and found a bad varactor in
the vco. If the frequency is high check the VCO control voltage. If it
is low the problem is in the oscillator if it is high the problem is in
the pll. Frank wa1gfz

-----Original Message-----
From: racal-bounces at mailman.qth.net
[mailto:racal-bounces at mailman.qth.net] On Behalf Of Bob Camp
Sent: Sunday, June 17, 2007 8:25 AM
To: I Z 6 E G K
Cc: racal at mailman.qth.net
Subject: Re: [Racal] RA 6790/GM Problem

Hi

If the VCO is running 10% high it is no longer running under crystal  
control. The first thing to suspect is the crystal. Grab any crystal  
you can find that is close to 22.75 MHz and hold it in the circuit.  
If the oscillator locks to the frequency of the new crystal then  
that's the problem.

Finding out what the specifications are on the correct crystal may be  
difficult. That will make ordering a replacement a bit tough. It may  
be easier to find a replacement board !!

Bob
KB8TQ



On Jun 17, 2007, at 8:00 AM, I Z 6 E G K wrote:

> Hello all,
> I'm experiencing an Out Of Lock condition with the BFO.
> Byte test always displays 04 error code.
> On the A8 board, in the area of 22.75 MHz BFO VCO, I can adjust L4  
> for a
> voltage reading on TP8 within specs (between 4.5 and 7 Volts DC)  
> but the
> frequency measured on J4 (BFO Output) slightly changes and it's far  
> from
> requested kHz 455. It's abt kHz 500.
>
> I understand that the Divided-by-50 frequency is abt MHz 25 and not  
> MHz
> 22.75.
> Any idea ?
>
> Mny tnx and 73
> Pierluigi IZ6EGK
>
>
>
>
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> RACAL at mailman.qth.net
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