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Multi Band AM/FM/SW Radio became only FM radio after over voltage supply

Discussion in 'Troubleshooting and Repair' started by Low Seng Kuang, Feb 8, 2018.

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  1. Low Seng Kuang

    Low Seng Kuang

    11
    1
    Jan 28, 2018
    bandHi,

    I just have a new cheap High Sensitivity Chinese AM/FM/SW Multiband Radio (Kchibo KK-2005A).

    The power consumption is heavy, I have replaced the two 1.5 volt size D (3V) battery with two 18650 Lithium Rechargeable Battery ( 8V) due to my curiosity and oversight.

    After this the SW bank is no more functioning, what it can receive now is FM Stations for all the 9 band.

    I guess that the high voltage might have damaged the delicate Integrated Circuit inside, and this radio now is damaged beyond simple repair unless somebody with professional knowledge.

    Am I right?

    Is there any good and easy solution for me.

    In the future, I will be very careful on the voltage issue of the power supply.

    Appreciate someone professional could comment on this issue.

    Thank you

    Low
     
  2. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    That type of radio tends to use a DSP-type chip for all functionality (with a separate audio amp) and both tuning and band-selection is achieved by selecting voltages from a chain of resistors in a voltage-tapping arrangement.

    If the chip itself hasn't been destroyed - and since it receives FM you might have been lucky, you may find that the resistive divider part has 'broken' such that the only voltage it outputs is the 'highest one' i.e. one end of the divider (or some part of it) has become open-circuit.

    Open it up and post a CLEAR picture of both sides of the circuit board and we can point you to where to take the appropriate test measurements.
     
  3. Low Seng Kuang

    Low Seng Kuang

    11
    1
    Jan 28, 2018
    Hi Kelly,

    Thank you for your explanation on the DSP Radio, I have opened up the radio but I find that all the componebts are niceky soldered to the baord, no wires were used, thus I concluded that the issue is due to damage chip,

    Thank you for your advise anyway.

    Low
     
  4. Low Seng Kuang

    Low Seng Kuang

    11
    1
    Jan 28, 2018
    Hi Kelly,

    I am writing back to you again because, I think is is too early for me to give up on trouble shooting the problem.

    I am sorry for not able to give you the picture of the board, as I do not have a smart phone to capture the image.

    The latest condition of the radio, is that FM station remain at the FM Band, SW station remains at SW Band as I change the band, selector, the problem now is that FM station is not stable, it vibrates and faded out. SW failed to capture any station, I can hear only the ripple wave hizzing sound.

    I have remove the circuit board from the casing for easy measurement.

    Overall the circuit board is very simple unlike the conventional radio.

    The folowing are the component;s location and the test result using a ANANG 8008 digital multimeter.

    1. Potential Meter (Tuner) 3 leg component , sum of resistance 1&3 = 1&2 +2&3, 1&2 and 2&3 changes are I move the dial - I assume this component id OK.

    2.Next to the band selector is a 6V 470 uF capacitor, testing with the component on the board shoes 799 UF when the polarity follows the marking, reverse making give a reading of 731 uF - I guess this component is faulty, can this cause the prsent conditions.

    3. Below the band selector there is a cylidrical silver coloured component, measuring 1.2 cm with a diameter of 3 mm, no marking indicatng what is it at the compenent or the circuit board, diode, capacitor, resistor I am not sure.
    I took the folowing readings:
    Capacitance mode: 0.43uF 0.23 uF reverse side
    Resistance mode: 4.632 M Ohm , Out of Range OL on the revese side
    Diode Mode 1.880V and 1.188V on the reverse side.

    4. At the centre of the board there is an 16 legs IC , 8 legs each side, very small 7mm x 1.5 cm.
    I do not know how to measure to determine its condition, do you need special equipmemt, I only have the digital multimter, appreciate if you could show the way.

    5. Other ICs are smaller ones, mainly squre shape measuring 1 cm x 1 cm, 6 legs 1 unit, 4 legs 1 unit, 2 legs 1 unit, 3 leg 1 units, may I know how to troble shhot.

    6. tHere is a larger capacitor next to the power transfomer 10V , 1000uF, both measuring 1.065Mf (right polarity and reverse polarity), AC supply code can produce the same effec as 3V DC supply, i assume it is ok.


    I hope my description above is giving you a snap shot of the circuit board, if not costly and subject to the availability of the component, I could try to replace the faulty component to restore the radio.

    Ceratainly I need your professional advise as I am a beginer in this area.

    Thank you very much

    Low Seng Kuang
     
  5. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    Is this the insides?

    KK-2005.png
     
  6. Low Seng Kuang

    Low Seng Kuang

    11
    1
    Jan 28, 2018
    Hi Kelly,

    This is the older version KK2005 (conventional radio). My one is KAIDE KK-2005A which is a DSP receiver (Dual Conversion).It does not have those inductors and variable capacitor tunner.
    The tuner is replaced by a 3 Pin Potential Meter (Variable Resistor).

    Certainly, my hope is to troble shoot the fault, appreciate if you could asist if you have the knowledge in this area.

    Thank you
     

    Attached Files:

  7. dante_clericuzzio

    dante_clericuzzio

    33
    2
    Mar 28, 2016
    Once it is damaged i believe the only way to get a new one...by the way i have tested a simple circuit based on the BK1079 to make FM radio and it works very well even on circuit board. Interestingly enough it actually does not even require an antenna to work and seeking the frequency channel just by a press of a button.

     
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