2238B FM alignment - where is L107?

[runningdog]

The 2238B service manual calls for adjusting trimmer C121 and oscillator coil L107. C121 is marked in the manual, it is the top one pointed to in the picture. But where is L107? Is it the coil that the second arrow is pointing to? I do not see it on the board layout in the sm.

It also calls for adjusting RF coil L104, which I also don't know where it is.

 

[ConradH]

Look at page 14ish of the manual where they show the layout of the tuner module. It looks like L107 in down the big square hole. It's probably a coil that gets adjusted by changing the spacing between the coils, not a slug type. My recommendation is not to mess with those unless absolutely necessary. It adjusts the low end and should be close just the way it is. That other coil is marked IF, so it's probably the IF coil, L105 or L106, not sure.

 

[runningdog]

Thank you ConradH! I wondered why there are holes to access the coils. I took a salvage one apart to see. The one you recommended to leave alone, L107, is glued...probably is best to leave it alone.

 

[rBuckner]

I believe Conrad is correct (no surprise here). Sometimes even the ones for the antenna gangs are the coils too the cheap so-and-so's!!

 

[catrafter]

Without an adjustable coil to set the low end local FM local oscillator, you can usually get the dial alignment OK by tuning all the way to the bottom of the dial, loosening the screws holding the tuning drum to the tuning capacitor and making sure the tuning fins are fully meshed and that the cap is against it's stop. You can now slip the drum on the tuning capacitor shaft to get the dial to agree with the low frequency alignment point. Tighten the screws and got to the top end of the dial and adjust the trimmer capacitor as per the manual for the high end, repeat the procedure until the dial agrees as best as possible over the entire tuning range.

All this so that the manufacturer could save a few cents.

Tom

 

[runningdog]

Thanks Tom. Which alignment point for the low frequency? 88MHz or 87.4MHz? The latter should match the tuning capacitor fully closed, but the scale on the dial face does not go out that far. This instruction in the manual has always puzzled me. It says to use 87.4MHz and 109MHz but those points are not on the scale to adjust to. And can you count on the fully open/closed tuning capacitor to always be 87.4/109MHz?

I did adjust the low frequency by tweaking the L107 coil. Prying on it gently with a plastic screwdriver did indeed get it spot on. You have to bend it slightly past where it needs to be and let it spring back into the correct position. Thanks again, ConradH.

 

[rBuckner]

I just use on-air stations and set the dial to them.

 

[catrafter]

Thanks Tom. Which alignment point for the low frequency? 88MHz or 87.4MHz? The latter should match the tuning capacitor fully closed, but the scale on the dial face does not go out that far. This instruction in the manual has always puzzled me. It says to use 87.4MHz and 109MHz but those points are not on the scale to adjust to. And can you count on the fully open/closed tuning capacitor to always be 87.4/109MHz?

I did adjust the low frequency by tweaking the L107 coil. Prying on it gently with a plastic screwdriver did indeed get it spot on. You have to bend it slightly past where it needs to be and let it spring back into the correct position. Thanks again, ConradH.

There are so many errors in the manuals, I figure out the 'value' of the spacing between each 'dot' or mark on the dial and then count down from the lowest number and up from the highest number to get the exact frequency of the end marks.

Tom

 

[Steven Tate]

Uh-oh. Sounds like math is involved. Let me get out my slide rule.