Yaesu FRG-7 repair

[rhb]

I bought one which has some issues.  The frequency is off by 10 kHz  at the low end and 90 kHz at the high end.  I suspect that it needs alignment as it appears to have been repaired.   I've also encountered a birdie that suggests there is a squeg, an unstable spurious oscillation, somewhere.

The user manual provides the alignment information and I have plenty of test gear.  However, I've never undertaken this level of radio diagnosis, so if someone has experience with the FRG-7 at component level I'd appreciate a chance to discuss the problems and what the spectrum should look like at various test points.

I'm using the spectrum analyzer feature of the Instek MDO-2000E series which has the major virtue of not putting my 8560A front end at risk from DC offsets as I don't yet have a DC block for it.

Have Fun!
Reg

Edit:  I've determined that the 3rd LO range is too large.  If I trim TC403 to set the LO at 3.445 with the dial at 0 it is at 2.35 at 1000.  I can't see how to correct that except to put a large cap in series with the air variable.  Comments?  This unit has the fine tune cap which I have set at midrange when it's centered.

[rhb]

After a much head scratching I sat down and did the algebra.  Based on measurement of the main tuning cap I calculated I needed an additional 56 pF in parallel.  After adding that across the fine tuning cap if is now exactly at 3.455 MHz at the 0 mark and 2.455 at the 1000 mark on the dial.

Except for measuring the main cap and the fine tuning cap, I took the other caps at the schematic value when I calculated what the minimum capacitance needed to be to swing 1 MHz from the 19 pF position to the 348 pF position.

That raises the question of whether it ever tuned correctly.  Though perhaps the ceramics in the LC tank were close to 20% over nominal when it was built.

All in all very strange.  I'd expected just to be able to adjust the trimmer cap and coil.

Have Fun!
Reg

[rhb]

I finished doing the alignment per the instruction manual.  Discovered an interesting cause for the squeggs.

The multiturn dial mechanism uses a stack of disks with lugs.  They had oxidized and were randomly introducint a large parallel capacitance which would drop the 3rd LO to 1/2 or less.  Or worse yet, be unstable.

A bit of Deoxit cured it.

An easy test for the issue is to set the radio on AM with no antenna and spin the dial quickly.  If you hear scratchy pot noise, put Deoxit on the dial stop plates and the rotor shaft bearings.

Have Fun!
Reg