02-15-2020, 03:37 PM
Nasty schematic to post...
http://www.nostalgiaair.org/Resources/do...008920.pdf
All but one IF can is commonly used that one is the ratio detector. Therefore, all IF cans should be O.K.
I suspect that the FM oscillator is not working. Try cleaning all contacts on any switches associated with FM with 91% alcohol, using an acid brush and cloth scraps to catch the excess. Careful not to snag a bristle from the brush. Blow dry with compressed air if available, follow with warm hair dryer or heat gun after being sure there are no residual alcohol fumes around... De-Oxit can cause leakage in sensitive switch circuits. Manipulate the switches carefully to be sure there has been no mechanical damage to the contacts, then exercise the switch at least 50 times. That should burnish the contacts. A tiny bit of lube oil on bushings and tiny dab of grease on the ball detent helps...
Be sure there is no De-Oxit in/on tube socket/pins...
If no joy, use a 20k ohms/volt meter for voltage checks, any other meter will tell a lie in respect to the schematic readings. Look for problems in the FM oscillator.
Since the chassis has had a lot of work, shorting wire clipping, solder blobs, solder flowed across tube contacts and tie terminals, wire whiskers from stranded wire, shorting. Poor riveted connections like socket ground rings and chassis grounding lugs. A meter will not show this faults so soldering the rivet and body of the lug to the chassis is a remedy or drilling out the rivet and using hardware with serrated washers.
If you have a generator injecting a 110.7 mhz into the oscillator coil may yield reception if the front end is tuned to 100mhz. Use an insulated link for this to avoid issues like a shock or fried generator level controls.
If no joy, plan on a stage by stage signal injection or tracing. May have to make simple instruments to do...
GL
Chas
http://www.nostalgiaair.org/Resources/do...008920.pdf
All but one IF can is commonly used that one is the ratio detector. Therefore, all IF cans should be O.K.
I suspect that the FM oscillator is not working. Try cleaning all contacts on any switches associated with FM with 91% alcohol, using an acid brush and cloth scraps to catch the excess. Careful not to snag a bristle from the brush. Blow dry with compressed air if available, follow with warm hair dryer or heat gun after being sure there are no residual alcohol fumes around... De-Oxit can cause leakage in sensitive switch circuits. Manipulate the switches carefully to be sure there has been no mechanical damage to the contacts, then exercise the switch at least 50 times. That should burnish the contacts. A tiny bit of lube oil on bushings and tiny dab of grease on the ball detent helps...
Be sure there is no De-Oxit in/on tube socket/pins...
If no joy, use a 20k ohms/volt meter for voltage checks, any other meter will tell a lie in respect to the schematic readings. Look for problems in the FM oscillator.
Since the chassis has had a lot of work, shorting wire clipping, solder blobs, solder flowed across tube contacts and tie terminals, wire whiskers from stranded wire, shorting. Poor riveted connections like socket ground rings and chassis grounding lugs. A meter will not show this faults so soldering the rivet and body of the lug to the chassis is a remedy or drilling out the rivet and using hardware with serrated washers.
If you have a generator injecting a 110.7 mhz into the oscillator coil may yield reception if the front end is tuned to 100mhz. Use an insulated link for this to avoid issues like a shock or fried generator level controls.
If no joy, plan on a stage by stage signal injection or tracing. May have to make simple instruments to do...
GL
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
