I have a GE C-525B table clock-radio that is unable to tune just one station on the FM band. A lot of stations come in at once. All the tubes have either tested good or have been replaced. At one time, if found that if I melted the solder on one end of the oscillator stator plates and shifted them so that they nearly touched the rotor plates, it would tune for at least one half of the band. Now that doesn't work, either. I have since then centered the plates again. If I squeeze the front and back of the chassis toward each other and/or try to spread them apart in the area of the antenna terminals, the radio will begin to tune for a while. The radio uses a printed circuit board chassis with a steel frame around it. I've been working with a schematic and can't fiqure it out. There are several soldered ground straps that connect them together, and they seem to be OK. I haven't found where running a jumper helps. Does anyone know what is going on or not working here? I've spent a month with this teaser and I offer thanks for any help with it. Bart

The first thing to do is to determine if possible if those other stations are all FM stations. If they are, try aligning the radio. If they are a mix of FM and AM, concentrate on the band switch or wiring of the switch. I would check the condition of the first RF coil (transformer) that is in the FM section. If it uses the one tube converter, it will be the only transformer. You may need to pop the can off and try resoldering the windings, as well as the solder tracks to the coil. There may also be a cap inside of the can, test it too, replace it if it is a paper type.

Is this one using just a 1 tube FM converter like an HCC85? If it is, try resoldering the solder tracks to the socket. If that does not work, swap the tube with one or two others.

For that matter, check your plate voltages if nothing so far has worked. See if they are about half to two thirds the voltage of the audio output. Slightly more should be okay, anything less, you should look at the resistor network that makes up the voltage divider for resistors that may be out of tolerance.

If this is one that uses two or three tubes, I would focus on the oscillator section, and possibly the switch or switch wiring, if the switch can move around at all, check to make sure that a wire has not broken off inside, and also make sure that the switch actually is functioning as it should. I would also look at the caps in the discriminator and the detector stages, or the limiter stage if so designed.

: I have a GE C-525B table clock-radio that is unable to tune just one station on the FM band. A lot of stations come in at once. All the tubes have either tested good or have been replaced. At one time, if found that if I melted the solder on one end of the oscillator stator plates and shifted them so that they nearly touched the rotor plates, it would tune for at least one half of the band. Now that doesn't work, either. I have since then centered the plates again. If I squeeze the front and back of the chassis toward each other and/or try to spread them apart in the area of the antenna terminals, the radio will begin to tune for a while. The radio uses a printed circuit board chassis with a steel frame around it. I've been working with a schematic and can't fiqure it out. There are several soldered ground straps that connect them together, and they seem to be OK. I haven't found where running a jumper helps. Does anyone know what is going on or not working here? I've spent a month with this teaser and I offer thanks for any help with it. Bart

Thank you! I just found your answer, so I haven't tried any of your ideas yet. To answer your question about the stations recieved, yes they are all FM. I use one of those manifying florescent lights on an arm and no interference comes through like it would with AM. I found after posting my problem that if I connect an antenna wire to the stator of the (I believe) oscillator section of the tuning capacitor, the radio seems to operate normally. I'm pretty sure that section goes to the oscillator because it has fewer plates than the other FM section. I already had the can off the first IF and resoldered the connections. There's a capacitor only on the secondary side which is a mica cap.

The front end uses a 19JN8 two section tube for the RF amp and FM converter. The plate voltage measured 85V as opposed to 80V specified, but that is while powering through a 150 Watt isolation transformer, which tends to supply increased voltage to light loads. So I would say voltage is normal. I'm beginning to suspect caps, but there are no paper caps in this set, just primarily disk caps which are normally pretty reliable. I made a print out of your suggestions for my shop. I hope one of them works.

Thanks again for helping me on this. Bart

: The first thing to do is to determine if possible if those other stations are all FM stations. If they are, try aligning the radio. If they are a mix of FM and AM, concentrate on the band switch or wiring of the switch. I would check the condition of the first RF coil (transformer) that is in the FM section. If it uses the one tube converter, it will be the only transformer. You may need to pop the can off and try resoldering the windings, as well as the solder tracks to the coil. There may also be a cap inside of the can, test it too, replace it if it is a paper type.

: Is this one using just a 1 tube FM converter like an HCC85? If it is, try resoldering the solder tracks to the socket. If that does not work, swap the tube with one or two others.

: For that matter, check your plate voltages if nothing so far has worked. See if they are about half to two thirds the voltage of the audio output. Slightly more should be okay, anything less, you should look at the resistor network that makes up the voltage divider for resistors that may be out of tolerance.

: If this is one that uses two or three tubes, I would focus on the oscillator section, and possibly the switch or switch wiring, if the switch can move around at all, check to make sure that a wire has not broken off inside, and also make sure that the switch actually is functioning as it should. I would also look at the caps in the discriminator and the detector stages, or the limiter stage if so designed.

: : I have a GE C-525B table clock-radio that is unable to tune just one station on the FM band. A lot of stations come in at once. All the tubes have either tested good or have been replaced. At one time, if found that if I melted the solder on one end of the oscillator stator plates and shifted them so that they nearly touched the rotor plates, it would tune for at least one half of the band. Now that doesn't work, either. I have since then centered the plates again. If I squeeze the front and back of the chassis toward each other and/or try to spread them apart in the area of the antenna terminals, the radio will begin to tune for a while. The radio uses a printed circuit board chassis with a steel frame around it. I've been working with a schematic and can't fiqure it out. There are several soldered ground straps that connect them together, and they seem to be OK. I haven't found where running a jumper helps. Does anyone know what is going on or not working here? I've spent a month with this teaser and I offer thanks for any help with it. Bart

As a follow up: I finally did locate and repair the reason the radio wasn't selectively tuning only one station at a time. The problem was in the local oscillator tank circuit. Evidently, a bad solder joint developed at the tank circuit coil. I used a grid dip oscillator to determine whether either the RF tuning circuit or the VLO was the problem. It showed a grid dip at the station frequency, but not at the VLO frequency. A frequency counter was used to set the grid dip oscillator frequency. Grid dip oscillators are still handy things to use. Bart

: The first thing to do is to determine if possible if those other stations are all FM stations. If they are, try aligning the radio. If they are a mix of FM and AM, concentrate on the band switch or wiring of the switch. I would check the condition of the first RF coil (transformer) that is in the FM section. If it uses the one tube converter, it will be the only transformer. You may need to pop the can off and try resoldering the windings, as well as the solder tracks to the coil. There may also be a cap inside of the can, test it too, replace it if it is a paper type.

: Is this one using just a 1 tube FM converter like an HCC85? If it is, try resoldering the solder tracks to the socket. If that does not work, swap the tube with one or two others.

: For that matter, check your plate voltages if nothing so far has worked. See if they are about half to two thirds the voltage of the audio output. Slightly more should be okay, anything less, you should look at the resistor network that makes up the voltage divider for resistors that may be out of tolerance.

: If this is one that uses two or three tubes, I would focus on the oscillator section, and possibly the switch or switch wiring, if the switch can move around at all, check to make sure that a wire has not broken off inside, and also make sure that the switch actually is functioning as it should. I would also look at the caps in the discriminator and the detector stages, or the limiter stage if so designed.

: : I have a GE C-525B table clock-radio that is unable to tune just one station on the FM band. A lot of stations come in at once. All the tubes have either tested good or have been replaced. At one time, if found that if I melted the solder on one end of the oscillator stator plates and shifted them so that they nearly touched the rotor plates, it would tune for at least one half of the band. Now that doesn't work, either. I have since then centered the plates again. If I squeeze the front and back of the chassis toward each other and/or try to spread them apart in the area of the antenna terminals, the radio will begin to tune for a while. The radio uses a printed circuit board chassis with a steel frame around it. I've been working with a schematic and can't fiqure it out. There are several soldered ground straps that connect them together, and they seem to be OK. I haven't found where running a jumper helps. Does anyone know what is going on or not working here? I've spent a month with this teaser and I offer thanks for any help with it. Bart