Yaesu FRG-7700 receiver tuning fault

There isn't a VFO capacitor. The radio uses phase locked loops. Operating manual: Service manual:

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.

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

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.