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Trying To Modify A Radio

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EdFab

May 4, 2017
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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.
 

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davenn

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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:

all the scanning and similar functions ... volume up down etc will all be controlled by a microprocessor
so the chances of reading the firmware, editing it and reloading it into the micro will be somewhere between
not likely and impossible


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?

all that those do is control the pre-programmed functions of the microP

you cannot have it forcefully continuously scanning else it will never stop and isn't likely to stop on a station
reread you instructions for the scanning mode .... once scanning there are no buttons pushed .........

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.


Dave
 

EdFab

May 4, 2017
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all that those do is control the pre-programmed functions of the microP

you cannot have it forcefully continuously scanning else it will never stop and isn't likely to stop on a station
reread you instructions for the scanning mode .... once scanning there are no buttons pushed .........

Dave...I don't want it to ever stop scanning. I don't even want to have to press the TUNER button to make it scan. As soon as the radio is turned on I want it to start scanning and never stop...effectively I want to make the radio think the TUNER button is constantly being pressed, which will make the radio continually scan. Can you give me some hints how to do this?
 

davenn

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Dave...I don't want it to ever stop scanning. I don't even want to have to press the TUNER button to make it scan. As soon as the radio is turned on I want it to start scanning and never stop...effectively I want to make the radio think the TUNER button is constantly being pressed, which will make the radio continually scan. Can you give me some hints how to do this?

why ? what is the point of that ? you cannot do anything with it when in that mode
 

EdFab

May 4, 2017
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why ? what is the point of that ? you cannot do anything with it when in that mode

I'm trying to modify the radio into a 'ghost box'. It was easy to do with an earlier version of this radio...the SAB-55A [A] version. All you had to do was cut a wire, and the radio would continually scan, playing the static and music as it did so. Later models, the SAB-55A [C] and the SAB-55A [LE] have different circuit designs, and are considered to be 'unhackable' by the paranormal afficionados.

A 'ghost box' is a radio that has been modified to continually scan throughout the band, continually cycling through it, and as it does so you can hear the static noise as it is scanning between the stations, and hear the music as it scans through the stations (of course, you can't really make out the words clearly). The radios that have digital tuners like this Jensen one are the ones that can be modified, some more easily than others.

Paranormal folks believe that these 'ghost boxes' can pick up communication from the spirit world.

If you're curious about these 'ghost boxes', do an internet search...you might find it interesting. Also, there's a youtube video that demonstrates how the Jensen SAB-55A [A] version can be modified into a 'ghost box'. The Jensen I have is the [LE] version with different circuitry than the [A] version.

So what I want to do is somehow make the radio think the TUNER button is always depressed.That's why I'm investigating the physical TUNER circuitry.
 

davenn

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That's I'm investigating the physical TUNER circuitry.


there is no physical tuner circuit ... as I said earlier, it's all done by the microprocessor
It will most probably control a synthesiser and PLL circuit
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Paranormal folks believe that these 'ghost boxes' can pick up communication from the spirit world.

Do I need to add the "WOO WOO" tag to this thread?
 
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