Russian Lomo (Biolam?) old monocular-coarse focus wheel slippage
The right hand shaft knob contains the coarse focus locking clutch adjustment mechanisim( big name-simple design). This solution applies if you have the model with the fine adjustment wheel mounted in the base and may or may not apply if your fine focus is in the left-hand knob.
Inside the right hand knob ( as viewed from the rear of the scope) is a threaded disk/nut which has two pins (Slightly and for reasons I don't understand: they are offset vertically, they have different pin diameters and different pin lengths) In theory, they lock into the bushing within the knob proper to keep tension on the clutches while keeping the knob from falling off.
The repair can proceed in two ways depending on if the disk/nut has totally been unscrewed from the focus shaft.
Gently pull the left knob and as you do turn it slowly to see if the pins reseat. If they do you'll feel a slight lurch outward of the knob. Hold gentle outward tension( so as the pins remain seated) as you turn the knob clockwise until the slippage in the clutches is so lessened that your knob is firm and the focus adjustment is operating to your liking.
IF that didn't work it is likely that the threaded disk/nut has come off the shaft and will need to be reset and screwed back down. The disk is easily cross threaded and you'll need tweasers or micro plyers or a hemostat and/or a flat headed finishing nail. Plus I recommend a small bottle of LOC-TITE(tm) semi-solid thread sealer--NOT the kind that freezes the threads
As you unscrew the knob counter clockwise pull on the knob to slid it off the shaft it should come off in your hand revealing about 6-8 washers on the shaft. These are the clutches so be careful not to loose them.
The knob should have a slight rattle and that is the disk nut. To get to the disk/nut put a small finishing nail head first into the shaft whole and push to release the plastic knob insert cover out being careful to not loose the disk/nut.
To clean the threads and insure an easier repair screw the disk onto the focus shaft to insure the threads are clean.
This next part works better with the scope lying on its left side.
This part is optional but not necessary to get the scope back in operation. Place a tiny amount of LOC-TITE thread sealer on the shaft threads. This will make the knob clutch adjustment more stiff but will also reduce the likelihood that the knob will be adjusted out too far again. The loosening occurs when the knob is turned before the operator realizes the pinion gear limit has been reached or by someone who dosen't understand correct opperation of the focusing assembly.. So long as the clutches are engaged the and there is no slack in tension the disk/nut shouldn't come off the shaft again.
Observe the pins in the disk/nut and match them up with the holes in the aluminium/brass knob bushing. You'll have to wiggle the disk around to get it reseated properly. Once you do, hold the disk firmly against the bushing to keep the pins seated as you put the knob back over the shaft, pushing it all the way down against the shaft.(The clutches are springy so don't worry about it locking in place just now).
You may prefer to hold the disk/nut and knob firmly with a finger and spin the left hand knob counter-closkwise for easier threading of the nut but remember this will also move the focus arm. Not a problem if you start with the focus in the range centered.
If using the right knob: Turn the knob clockwise feeling for the threaded shaft maiting back up with the threads. IF it cross-threads, back it off try again. Once the threads are engaged keep the outward tension on the knob so the pins don't slip out. When you/ve screwed it down far enough, the clutches will take up the slack and keep the knob from slipping away from the disk/nut. You'll know the clutches are engaged when the focus shaft turns.
If you are happy with the repair slip the knob cover back on and snap in place. It if falls out place a little of the thread sealer on the rim and try again.
If you like this solution it took me an hour to write it up. Please consider volunteering an hour with a local non profit. I support the American Red Cross, Habitat for Humanity and the USO.
Mar 27, 2009 |