I’ve got a Jensen armband radio, model SAB-55A [LE], that I would like to modify. My level of electronic knowledge is very rusty. I was an electronic technician in the navy years ago, but I’ve probably forgotten more than I know, and I was never very knowledgeable about RF circuits. I’ve uploaded 4 photos, the front and back of the radio, and two photos showing the circuit board.
The way this radio normally works is that when you depress either the ‘down’ or ‘up’ TUNER button, the sound will cut out and the radio will scan through the band until the button is released, at which time it will continue to scan, finally stopping when it locks on to a good signal, and then the sound comes back. If you keep the button depressed long enough, it will reach the end of the band’s frequency range, then jump to the ‘other’ end of the band (the high end for the ‘down’ button, for example) and continue scanning. As long as the button is depressed, the radio will keep scanning through the band, and there is no sound.
What I want to do is modify the radio so that it will ALWAYS scan through the frequencies, not having to depress the TUNER for this to happen, and I want to hear the sound (noise as it’s scanning between stations, music as it’s scanning through a station).
I don’t have a schematic for this radio. I really have no idea how it’s doing what it’ doing. But there are some things I think I have figured out:
In the photo that has the pen lid in it, I’ve exposed part of the circuitry that the ‘down’ TUNER button activates. In the vicinity of the pen lid, there is an outer gold ring on the circuit board, with a solid gold circle in its center (please pardon this vernacular-impaired description). The silver-colored circular foil normally lays over the gold foil in such a way that the center of the silver foil coincides with the center of the inner solid gold circle. The pen lid is there to hold the silver foil out of position so that the gold foil exposed.
If you look at the center of the silver foil, you can see what looks like a little ‘indented circle’. Normally, that indented circle sits right over the solid gold circle.
The TUNER button itself is made of plastic, and on its underside there is a knob that protrudes down and aligns perfectly with the ‘indented circle’ of the silver foil. When the TUNER button is depressed, the knob on the underside of the button pushes against the indented circle of the silver foil, causing it to bend out of position and make contact with the solid gold circle. And wallah, the radio starts to scan, and the sound cuts out.
I have verified that the indented silver circle makes contact with the solid gold circle ONLY when the TUNER button is depressed. That ‘indented silver circle’ feels and acts like a switch. I’m guessing that when the ‘indented’ circle in the center of the silver foil makes contact with the solid gold circle, it creates a short between the outer gold ring and the inner solid gold circle. And somehow that causes the radio to start scanning and for the sound to cut out.
If that is correct, then making a solder connection between the outer gold ring and the solid gold circle would make the radio scan continuously, right?
But I’m not sure if I’m correct about this. The indented silver circle is much smaller than the solid gold circle, so it stands to reason that other parts of the silver foil might be in contact with the gold circle even when the TUNER button is not depressed, which means that there would ALWAYS be a short between the outer gold ring and the inner gold circle, right?
My Fluke won’t be delivered for a few days, and right now I don’t have a multimeter to do any checking. I have a breadboard, so in a few days I should be able to power this radio up while it’s apart and tinker around a bit.
What I know for sure is that depressing the TUNER button causes the indented silver circle to come into contact with the solid gold circle, and when that happens, then the radio begins to scan and the sound cuts out.
I could try this:
1) Check out the short theory by soldering a short between the solid gold circle and the outer gold ring, or
2) put enough solder on the gold circle so that it is always in contact with the indented silver circle (because that IS when the radio scans).
If there’s anyone here with a general familiarity with how this type of tuner circuitry is working, that would be great.
The way this radio normally works is that when you depress either the ‘down’ or ‘up’ TUNER button, the sound will cut out and the radio will scan through the band until the button is released, at which time it will continue to scan, finally stopping when it locks on to a good signal, and then the sound comes back. If you keep the button depressed long enough, it will reach the end of the band’s frequency range, then jump to the ‘other’ end of the band (the high end for the ‘down’ button, for example) and continue scanning. As long as the button is depressed, the radio will keep scanning through the band, and there is no sound.
What I want to do is modify the radio so that it will ALWAYS scan through the frequencies, not having to depress the TUNER for this to happen, and I want to hear the sound (noise as it’s scanning between stations, music as it’s scanning through a station).
I don’t have a schematic for this radio. I really have no idea how it’s doing what it’ doing. But there are some things I think I have figured out:
In the photo that has the pen lid in it, I’ve exposed part of the circuitry that the ‘down’ TUNER button activates. In the vicinity of the pen lid, there is an outer gold ring on the circuit board, with a solid gold circle in its center (please pardon this vernacular-impaired description). The silver-colored circular foil normally lays over the gold foil in such a way that the center of the silver foil coincides with the center of the inner solid gold circle. The pen lid is there to hold the silver foil out of position so that the gold foil exposed.
If you look at the center of the silver foil, you can see what looks like a little ‘indented circle’. Normally, that indented circle sits right over the solid gold circle.
The TUNER button itself is made of plastic, and on its underside there is a knob that protrudes down and aligns perfectly with the ‘indented circle’ of the silver foil. When the TUNER button is depressed, the knob on the underside of the button pushes against the indented circle of the silver foil, causing it to bend out of position and make contact with the solid gold circle. And wallah, the radio starts to scan, and the sound cuts out.
I have verified that the indented silver circle makes contact with the solid gold circle ONLY when the TUNER button is depressed. That ‘indented silver circle’ feels and acts like a switch. I’m guessing that when the ‘indented’ circle in the center of the silver foil makes contact with the solid gold circle, it creates a short between the outer gold ring and the inner solid gold circle. And somehow that causes the radio to start scanning and for the sound to cut out.
If that is correct, then making a solder connection between the outer gold ring and the solid gold circle would make the radio scan continuously, right?
But I’m not sure if I’m correct about this. The indented silver circle is much smaller than the solid gold circle, so it stands to reason that other parts of the silver foil might be in contact with the gold circle even when the TUNER button is not depressed, which means that there would ALWAYS be a short between the outer gold ring and the inner gold circle, right?
My Fluke won’t be delivered for a few days, and right now I don’t have a multimeter to do any checking. I have a breadboard, so in a few days I should be able to power this radio up while it’s apart and tinker around a bit.
What I know for sure is that depressing the TUNER button causes the indented silver circle to come into contact with the solid gold circle, and when that happens, then the radio begins to scan and the sound cuts out.
I could try this:
1) Check out the short theory by soldering a short between the solid gold circle and the outer gold ring, or
2) put enough solder on the gold circle so that it is always in contact with the indented silver circle (because that IS when the radio scans).
If there’s anyone here with a general familiarity with how this type of tuner circuitry is working, that would be great.
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