1. Remove the PTO mini BNC from J217.
2. Turn the radio on its back and remove the anti-backlash spring from the Oldham coupler. Store this in a safe place.
3. Loosen the spline screw securing the front flange of the Oldham coupler to the gearbox and pull it back to release the center disc of the coupler. Store this in a safe place.
4. Now remove the PTO. You do not need to pull the front panel to do this. Just loosen the two screws fastening the rear bracket to the chassis and disengage the three green headed screws holding the PTO to the chassis. The PTO can now be withdrawn. Place it conveniently on
the radio so the power connector can remain connected.
5. Connect your frequency counter to the PTO output connector. To do this you need a mini-bnc to bnc adaptor. If you don't have one of these just remove the one that is attached to the
rear apron and use that.
6. Switch the radio to standby and allow the PTO to stabilize for about an hour. Be sure the ovens switch is OFF.
7. Manually rotate the PTO shaft until the counter reads 2.45500 MHz. Mark the position of the shaft on the mounting plate. I use the anti-backlash spring post as an index.
8. Now rotate the PTO shaft 10 turns until the index lines up again. The counter should read 3.45500 MHz but of course it won't otherwise you would not be going to all this trouble!!
So now turn the end point adjusting screw until the counter does read 3.45500 MHz. You need a thin screwdriver to do this. Be careful not to lose the access cover screw,
9. Check the index once more at 2.45500 MHz. If it does not line up then repeat steps 7,8,9 until the range of the PTO is exactly 1 MHz for ten turns of the shaft.
10. Before you replace the PTO check the setting of the 10 turn stop. In its fully counterclockwise position the dial should read between -963 and -972. If it is outside this range adjust the ten turn stop until it does. If the error is minimal the best way to do this is to loosen the small bevel gear on the counter and reset it. After doing this be sure to check the mechanical synchronization.
The check point is 2.000 MHz for the R-390 and 7.000+ for the R-390A.
10 Now replace the PTO using the reverse procedure but do not tighten the spline screw on the Oldham coupler. Set the KHz readout to +000, rotate the PTO shaft until the couter
reads 2.45500 MHz and then carefully tighten the spline screw and reconnect J217.
Thats all there is to it and it should not take more than 10-15 minutes. If the end point adjustment is out of range then you have a much more difficult problem. This involves dismantling
the PTO and removing one turn from the appropriate coil. This is another subject. If you have such a problem let me know. I may be able to help.