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Tiny FM Radio Chip

Discussion in 'Electronic Repair' started by mv, Nov 19, 2003.

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  1. mv

    mv Guest

    Hello,


    I bought a tiny FM radio (made in China!) that has a chip in it


    The Chip looks like SDC 304M (Cant make out exactly) and has digits
    088
    The rest of the radio contains the amp, coils and capacitors.


    Now, on to my problem - The radio has "Reset" and "Scan", the radio
    was probably manufactured for use in the US so the FM Frequency
    increments are different from those used here in India. This means bad
    reception. How can I fix this? Lots of people will be very pleased if
    they could get better sound from these nifty devices.


    Thanks in advance.

    mv
     
  2. Jerry G.

    Jerry G. Guest

    I have seen these radios. The frequency scan allocations are software
    within the chip. There is nothing externally that you can do. See if you
    can find out who is making these radios in China, and contact them to know
    if they can make a model with the proper allocation.

    If you offer to sell these for them, they may even go along with some type
    of agreement. These manufactures are constantly looking for new markets.

    --

    Greetings,

    Jerry Greenberg GLG Technologies GLG
    =========================================
    WebPage http://www.zoom-one.com
    Electronics http://www.zoom-one.com/electron.htm
    =========================================


    Hello,


    I bought a tiny FM radio (made in China!) that has a chip in it


    The Chip looks like SDC 304M (Cant make out exactly) and has digits
    088
    The rest of the radio contains the amp, coils and capacitors.


    Now, on to my problem - The radio has "Reset" and "Scan", the radio
    was probably manufactured for use in the US so the FM Frequency
    increments are different from those used here in India. This means bad
    reception. How can I fix this? Lots of people will be very pleased if
    they could get better sound from these nifty devices.


    Thanks in advance.

    mv
     
  3. When I opened one up (they are down to 99 cents here in Canada) and
    after doing some searches, and a bit of tracing, it turned out to
    be a Phillip's IC, the TDA7088. I thought it might be a surface
    mount TDA7000, and of course that did not match the number of pins on
    the IC, but Phillips listed some similar ICs, and one matched in
    pin numbers, and when I traced the circuit it was a match.

    Below is something I posted when someone asked about this IC before.

    I haven't read the datasheet in a while, or maybe not carefully,
    but it scans with an analog voltage, with one of the buttons
    starting the ramp, and the other button resetting it to start.
    There's circuitry in the IC for detecting when the radio is tuned
    properly to a station, which then halts the ramp.

    I assumed the ramp was not stepped, for the simple reason that
    the varicap used to tune the thing would not be linear, so a given
    step at one end of the dial would not move the radio to the next channel
    at the upper end of the dial.

    Given that assumption, and you can read the datasheet to see if I'm
    wrong, I would think the radio would work no matter how a given
    country's FM stations are spaced.

    Now, if the question is actually that the FM band in India is
    different from that in North America (88 to 108MHz), then it's
    a matter of changing the coil (or maybe just squeezing or spreading
    it if the difference is little) so it does cover the proper frequency
    range.

    Michael
    -----------------------------------------------------------
    I bought one of those recently, when they were on sale for $1.99 at
    Pharmaprix (which is Shopper's Drug Mart in the rest of Canada).
    I was simply curious about what was inside, and the price became
    low enough that I didn't mind spending the money.

    I had problems reading the IC at first. So I started out tracing
    the circuit. At first, I thought/hoped it was the TDA7000, but
    the pin count was wrong. I looked up that IC at the Phillips'
    site (it was easier than trying to find where I'd stashed the
    paper datasheet), and they made mention of similar ICs, including
    two that had that tuning scheme. I went through them, and
    the match was the TDA7088. Looking more carefully at the IC,
    the "7088" was now visible, though it looked like it was a knockoff
    or a cheap second source, rather than an IC that came from Phillips.

    I'd say this is the same IC, since your "1033" could be a misread
    of "7088". Check the datasheet at
    http://www.semiconductors.philips.com/pip/TDA7088.html

    Likely by comparing the pinout from it with the actual circuit, you
    will find a match.

    I was going to post something about my findings, because they are a curiosity.
    But I'm not sure where my notes are, or even where I put the circuit board.

    The IC uses the same scheme as the TDA7000, ie a conversion to an IF
    of about 70KHz, where an active filter can be used for selectivity.
    And one of those Frequency Lock Loops which reduces the apparent deviation.
    Then they throw in the circuitry for the tuning scheme.

    Having once seen someone suggest using the TDA7000 as a direct conversion
    receiver (when they were readily available at Radio Shack), they claimed
    the mixer was double balanced, I couldn't help but think maybe these
    radios would be a cheap local source for a mixer. Leave the IC on
    the board, and just strip the unneeded parts of, wiring to the board
    rather than wiring to that smd IC. I assume the big problem would
    be that since the 7088 can't handle more than about 3V on the supply
    line, it will be even worse for signal handling than the NE602 is said
    to be. (And I am simply assuming it's a double balanced mixer.) But
    for a couple of dollars, there are times when someone might need
    a mixer that these radios can supply cheap and locally.

    Michael
     
  4. mv

    mv Guest

    Thank you for pointing me to the Datasheet.
    Michael's answer wins ;-)
    The chip seems to be sc1088 from HANGZHOU SILAN MICROELECTRONICS, same
    as the Philips TDA7088T.

    Now, how do I fix the problem? I have already tried expanding the
    coil, the radio stopped working, until I squeezed it back again. Any
    other low tech procedure would be appreciated. Will changing the ramp
    steepness improve sound Quality?

    Thanks
    mv
     
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