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48-482 no SW - Printable Version

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48-482 no SW - DCASAZZA - 10-12-2009

Has anyone experienced a 48-248 with no SW and found the fix?

I have no SW reception and a scope shows no osc in SW mode. SW osc coil coninuity is OK.
Total recap exept for the mica types. All resistors checked and most replaced including some very hidden ones.
AM and FM work pretty well. I have aligned the IF but not touched the front end. I have swept the SW band with a signal generator with no result. I'm working from a Riders manual and the detail is poor and correct ID of the Mica types not good. I realy don't want to do a mass change out of these unless I have to.

Any ideas ?

Still need a power transformer but a smart tap "healed" this for now.

Re: 48-482 no SW - DCASAZZA - 10-17-2009

FOUND IT! Another very hidden resistor on the push button switch deck 22k inside spagetti tubing under wires and caps w/ short leads. Replaced it and it sings like a bird on SW band.

I did a over the air alignment for AM and FM and IF's. I touched up the FM1000 coil /cap but returned to original positions. Sounds pretty good so why recreate the wheel. My Rider diagram is not real clear. Does anyone have a recomendation as to calibrating the SW Osc trimmers?
I may just leave it alone.

Re: 48-482 no SW - exray - 10-17-2009

It looks like the SW adjustments are included under the "AM alignment" instructions.

Re: 48-482 no SW - DCASAZZA - 10-18-2009

They are, but the right side of my physical picture showing layout and the one showing whick C-xxx is for what in the Riders PDF is cut off. The schematic is blurry also (strike three). I experimented and determined which trimmers affect SW oscilator but not sure which is the main osc adjust and which one is the trim for the low end of the band. They do interact of course, but combined with late night fatigue I wasnt getting anywhere. I assume the ant trim for sw is the trimmer at the rear of the chassis.

Re: 48-482 no SW - Sean - 10-18-2009

Dave,

Try the Philco service bulletin on this page:

http://www.audiophool.cjb.net/Philco.html

You will have to scroll down to the 1948 section. I'm working on one of these sets currently and hope to have the recap finished today.

Re: 48-482 no SW - DCASAZZA - 10-18-2009

Thanks Sean

This is much clearer very clean copy. It looks much like the Riders in format, maybe this is where Riders got their Info from. I'm a creature from the TV era and Sam's service info and I know they almost always re worked the schematics to their format which was really pretty good.
Thanks again

Dave