Basic GE AA5 Clock Radio - No Signal at one end of the band?

[Dubis7]

Decided to pull my GE C-403 clock radio off the shelf and get it going again. The electrolytics were dead of course, and I went ahead and replaced C2, which was a paper cap. The schematic (which I've attached) reads 47mmf, but when I took it out the actual cap was .047. I replaced it with a spare of the same value I had on hand, swapped out the filter caps and got it working!

Except!

When I tune it to the lower end of the band, the signal completely dies. Just some crackling. I also noticed that the actual stations seem to be just a hair off what they are on my other AA5 set that I restored, but that may just be from the simplicity of the circuit.

Fiddling with the two transformer adjustments did nothing, and there are few parts left to even replace. I even went ahead and swapped C2 with a 47PF capacitor I had ordered, which only killed my signal until I swapped it back. Is anyone familiar with this sort of problem?

Video of the symptom is here:

https://photos.google.com/share/AF1Q...VIY3YyelVZZVNn

[Electronic M]

The tuning cap plates could be touching and shorting signal.

Dial off frequency across the board can be compensated for with an osc trimmer on most AA5s.

[Dubis7]

I did notice it starting to rub a little when it reaches that point. You can actually hear physical scratching. What's the solution? Just bend the plates a little so they don't touch?

Oscillator coil would be L2 in this case, right? That's a fixed coil on mine - looks like it might just be the nature of this beast.

[Electronic M]

Originally Posted by Dubis7

I did notice it starting to rub a little when it reaches that point. You can actually hear physical scratching. What's the solution? Just bend the plates a little so they don't touch?

Oscillator coil would be L2 in this case, right? That's a fixed coil on mine - looks like it might just be the nature of this beast.

You can bend plates to stop rubbing. Be careful that you're bending the right one(s) or you'll be making new rubbing...

Usually there are 2 screws on the side of the tuning cap that are adjustable open air mica insulated trimmer caps near terminals on the tuning cap. If there's no FM the osc trimmer will be the adjustment screw on the side of the smaller set of fixed plates on the tuning cap. The service manual often calls out a procedure for setting both the osc and tuning sections of the variable cap (and RF section if if we're an AA6 and there's an RF amp stage).

[Dubis7]

Good news - I was able to find the shorting plate and adjust it. Radio receives all across the band now!

I think I saw the screws you're referring to. I'll play a bit with those and see if I can align the band a bit better. That should get it going. Thanks!

[zeno]

Originally Posted by Dubis7

Good news - I was able to find the shorting plate and adjust it. Radio receives all across the band now!

I think I saw the screws you're referring to. I'll play a bit with those and see if I can align the band a bit better. That should get it going. Thanks!

Those are trimmer caps not screws. Use a plastic tool & dont turn far.
Always use plastic for alignment. Metal can detune it & break transformer cores.
Its often a good idea to "flag" your tool so you can go back to start if need be.

Zeno
LFOD !

[Dubis7]

Got it! Yeah I have a plastic adjustment screw set I use for these. I think the clock radio is about as good of a performer as it's gonna be - these weren't meant for HIFI setups. It's just nice to have an easy afternoon project now and again.