04-17-2009, 01:37 PM
Johnny,
Before you play around with injecting signals, I'd try to clean your band switch contacts. Dirty contacts could easily block the signal. Are you sure the oscillator works? In the steps below I am assuming you have confirmed that.
You can probably assume for now that the radio works from the first IF coil forward since you are getting that radio station when you connect your meter to the XXL plate. If you have a signal generator, start by injecting a 455 KHz modulated signal onto pin 6 of the "first detector" XXL tube through a .1 uf cap. If you hear the tone, then you know the first detector and everything forward works. If you don't hear anything, you might try scanning the signal generator back and forth a little in case your IF coils are misaligned. (You could take the time to align the IF coils now if you do hear a tone.) If you hear nothing, replace the XXL tube. If still nothing, suspect the bypass cap or bias resistor on the XXL grid.
If the first detector works, then move the signal generator to the antenna section of the tuning condenser, as described in the alignment instructions for this radio. If you get nothing, then I'd suspect the band switch or the coupling capacitor part 4.
If you hear the tone at the tuning coil, then move the signal generator to the antenna terminal for the broadcast band. (Red antenna wire, I think, but please confirm for yourself.) Usually you can hear a 455 KHz modulated tone even without shorting the oscillator. If you hear nothing, it could still be the band switch, or maybe the antenna transformer part 3 or the antenna coil part 8. Check the continuity of those parts and see what you get. That should isolate the problem to either the band switch, the transformer, or the coil, unless by some chance something is mis-wired. If you get a tone straight through from the antenna terminal to the speaker, but still no music, then I'd suspect something in the oscillator section is open, like maybe coil 13 or caps 31 or 24.
Good Luck.
Before you play around with injecting signals, I'd try to clean your band switch contacts. Dirty contacts could easily block the signal. Are you sure the oscillator works? In the steps below I am assuming you have confirmed that.
You can probably assume for now that the radio works from the first IF coil forward since you are getting that radio station when you connect your meter to the XXL plate. If you have a signal generator, start by injecting a 455 KHz modulated signal onto pin 6 of the "first detector" XXL tube through a .1 uf cap. If you hear the tone, then you know the first detector and everything forward works. If you don't hear anything, you might try scanning the signal generator back and forth a little in case your IF coils are misaligned. (You could take the time to align the IF coils now if you do hear a tone.) If you hear nothing, replace the XXL tube. If still nothing, suspect the bypass cap or bias resistor on the XXL grid.
If the first detector works, then move the signal generator to the antenna section of the tuning condenser, as described in the alignment instructions for this radio. If you get nothing, then I'd suspect the band switch or the coupling capacitor part 4.
If you hear the tone at the tuning coil, then move the signal generator to the antenna terminal for the broadcast band. (Red antenna wire, I think, but please confirm for yourself.) Usually you can hear a 455 KHz modulated tone even without shorting the oscillator. If you hear nothing, it could still be the band switch, or maybe the antenna transformer part 3 or the antenna coil part 8. Check the continuity of those parts and see what you get. That should isolate the problem to either the band switch, the transformer, or the coil, unless by some chance something is mis-wired. If you get a tone straight through from the antenna terminal to the speaker, but still no music, then I'd suspect something in the oscillator section is open, like maybe coil 13 or caps 31 or 24.
Good Luck.
John Honeycutt
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