[R-390] R-390A BFO PROBLEM

[Flowertime01 at wmconnect.com]

Harold,

You describe a common problem as follows,

Ever since the 3TF7 Ballast tube went out, I have had a BFO problem. I need 
to get to the BFO Tube socket beneath the chassis. To do this safely, I need to 
pull the BFO Drive Shaft forward. But I can't get the coupling unit nearest 
the BFO Tuning Unit to release. I have removed both set screws and put a few 
drops of penetrating oil in the holes with no success. However, I can hold the 
shaft coming from the Tuning Unit with long nose pliers and can turn the 
coupling unit with my hand. I am reluctant to put more pressure in this area in fear 
of damagng the tuning unit or the "Bellows" type device between the two 
shafts.

------------------
The problem is a bur on the shaft inside the bellows. Even though you have 
both spline screws out of the end of the bellows coupling the bur still has the 
shaft lodged into the bellows.

There are a couple things you can do.

Option one, if the IF deck bushing is installed with the nut to the inside of 
the IF deck, some are some are not, you can remove the nut from the chassis 
bushing, remove the spline screws from the BFO end of the bellows, compress the 
bellows off the end of the BFO shaft, tilt the shaft and bellows a bit, and 
work under it.

Option two, you can grip the bellows hub at the extention shaft end, with a 
pair of pliers, put a knob back on the shaft section and thus use the knob for 
leverage and the pliers to hold the hub. This should give you enough leverage 
to dislodge the shaft from the bellows coupler.

Once you get it apart you can clean the burs off the shaft with a file. You 
will likely need to clean a bur off the shaft from where you installed the 
knob. You need that end of the shaft clean as it goes back into the shaft 
extension bushing.

When you reassemble the bellows coupling you will want to expand the bellows 
a bit (1/8" inch) so that as the BFO shaft screws in and out over the tuning 
range zero is in the middle of the bellows travel. There should be about equal 
stress on the bellows as it travels from -3 to 0 to + 3. about 270 degrees of 
rotation.

New replacement bellows are available at a cost.
Good used bellows are available.

Getting out the acid core solder and a torch, the bellows can be rebuilt.
The bellows will unsolder from the brass hubs and can be reworked if they 
have been abused.

But think a head a bit, when you reassemble the parts. Clean all the burs off 
the shaft so it works nice in the bushing, fits nice into the extension 
shaft, and fits nice into the bellows hub. Some mechanical alignment may also be in 
order. The BFO can should line up with the shaft center line with no offsets 
of angel. Exact may not be achieved. But what you had did work and would still 
be OK. Just get it back to gather as nice or better than it was before you 
took it apart.

You can grab the hub with a pair of pliers and apply force to the shaft to 
twist things apart. Just grip things on the correct end so you are not applying 
force across the bellows.

Roger AI4NI   </HTML>