Yaesu FRG-7700 receiver tuning fault

[Lucifer]

I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.

 

[Fox's Mercantile]

On 12/1/18 11:38 PM, Lucifer wrote:

I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.

There isn't a VFO capacitor. The radio uses phase locked loops.
Operating manual:
<http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_user.pdf>
Service manual:
<http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_serv.pdf>


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

 

[Lucifer]

On Sun, 2 Dec 2018 01:31:27 -0600, Fox's Mercantile <jdangus@att.net>
wrote:

On 1/12/18 11:38 PM, Lucifer wrote:
I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.


There isn't a VFO capacitor. The radio uses phase locked loops.

Thank you for your reply and the manual links, however you are
wrong about the VFO capacitor.
It uses the PLL to select the band and the VFO to tune within the
band. The Kenwood R-1000 works the same way.

Operating manual:
http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_user.pdf
Service manual:
http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_serv.pdf

 

[Arie de Muynck]

On 2018-12-02 06:38, Lucifer wrote:

I suppose an amateur radio group would be better but they
are very quiet.

There is a lively and helpful Facebook group of Yaesu users, look for
"Yaesu-FOX-TANGO". Describe your equipment and take the exam :-;

Arie de Muijnck

 

[Lucifer]

I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.

 

[Dave Platt]

In article <cqje6edjk5aqrc9g2rrojqje26ahl1l0h7@4ax.com>,
Lucifer <LuciferMorningstar@bigpond.com> wrote:

I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.

That's possible. It may be purely mechanical - a loose tuning cord (I
can't tell if the design uses one), or a loose shaft coupling, or an
obstruction (e.g. bent plate on the capacitor, or a small dead
cockroach, or etc.) which binds the mechanism at some point in its
rotation.

It's also possible that there's something wrong with one of the
circuits to which a variable-capacitor section is connected. For
example, the VFO might be stopping entirely when you try to tune it
into part of its range. This might indicate (e.g.) a weak transistor,
or a capacitor that has become leaky... something which causes the
gain inside the oscillator loop to drop below 1.

Best way to distinguish would probably be to hook a frequency counter
and/or o'scope to the output of the VFO unit. Tune it through its
range, and see if you get a reasonable output signal throughput the
range.

If the VFO produces a consistent signal, then the next suspect would
be the PLL board, which generates the IF frequencies by multiplying
the output of the VFO. The PLL might be losing lock for some reason,
and shutting down. If the VFO works OK, then scope/count the IF
outputs from the PLL, and see if they vanish suddenly or get "stuck"
somehow.

The manual has the alignment procedures.

You should also do an "eyeball" inspection to look for obvious
failures, such as bulging or leaking electrolytic capacitors. These
units are old enough that it might have been built with some 'lytics
that suffer from the faulty-electrolyte "capacitor plague". If so, a
careful re-capping (with repair of any damaged traces on the board)
would be called for.