I guess I should know better by now.
My 48-482 just didn't sound good on FM and didn't pull in many stations so I thought I'd go over the alignment again, now that my good sig gen is working.
Bad mistake. As I went to adjust one of the cans (C403) as soon as I touched it I lost my tone and the set went michrophonic. If I tapped it it would work briefly.
OK, so I removed it and opened it up. I tested the mica cap inside and it was within specs. I checked the trimmer and couldn't see anything so I gave it a quick spray with Deoxit and reassembled it and reinstalled it. Nothing!
I managed to get the cover off while it was still connected and when I touch the top of the IF transformer (the ceramic part), I get a tone. if I put a screwdriver to the bad trimmer and touch the blade I get a tone.
What did I do now and how can I fix it?
Thanks,
You made sure that C403 tested continuous, right? I'll assume you did, and it's okay.
I recently tried going through the whole FM alignment procedure in the Philco manual (with some proper supervision), and was fairly successful.
Ground the plate of the FM1000, make the loading network as described in the instructions, and then, after hooking your generator up to L501B (middle coil under the tuning cap) & setting it to 9.1 MHz, clip the loading network to the top padder of C403b and ground, and then adjust the trimmer fro C403c. You're neutralizing the adjacent coil with that loading network & that will enable you to zero right in on the 9.1 Mhz modulated tone.
Do that across all the IF cans and see what you get.
Hold off on adjusting the FM detector (C300b & TC300) for now. Just get the IF chain lined up well.
My problem isn't alignment, it's C403 as I stated in my post.
Thanks
Okay, back to my first point. Did you test the continuity of C403?
I may not understand something, but: how does a cap test continuous?
My mistake. it's the cap that trims Z503.
Possibly there's intermittent contact in that trimmer, or maybe between the pins and the socket of the 7H7 tube next to it.
OK, so here's where I'm at now: I have a 2nd 48-482. I took the IF transformer out and installed it in the first one. With my signal generator connected and set to 9.1Mhz, If I touch the same trimmer on the replacement I get a tone if the screwdriver is touching it. When I remove the screwdriver, no tone.
By the way both have continuity.
Any thoughts?
Thanks,
Eric
Make sure you are using non-conductive screwdriver/socket. (Also when adjusting magnetics - non-ferrous or better yet - plastic ones).
If you don't have the proper tools, you can file down a chopstick to the right size. If you cut too much or wear the D**n thing out, snip the off the problem and file file again.
I have the correct tools. I think I'm having trouble getting my point across, sorry. The problem is: with the sig gen connected per the alignment instructions I get no tone. If I adjust it with the diddle stick I get no sound. If I touch a screwdriver to the trimmer in Z403 I get a tone.
Eric
It is hard to get the point as if you touch a trimmer cap (without pressing) with an insulated took nothing should be happening at all.
Now here's a guess: when you touching it you do fix some cold soldering spot which developed long time ago and you triggered it when first touched the cap.
Take a soldering iron.
Turn the radio fully off / unplug it from the AC.
And touch up with a goodly portion of a rosin flux EVERY contact around that can be possibly flexed when you touch the C404.
All of them - coils and caps.
Then tell us the result.
You almost got it. What I meant was that if I touch it with an insulated tool nothing happens. If I touch it with a metal screw driver, I get a tone. Am I still looking for a cold solder joint?
Sounds like the metal screwdriver is acting like an antenna and picking up the signal from the generator or a previous stage. Where are you connecting the signal generator?