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110V/220V switch in an old power supply

Discussion in 'Troubleshooting and Repair' started by Richard9025, Apr 10, 2017.

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  1. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    Hi !
    I recently got a radio that doesnt start (no sound , just buzzing from the transformer) .(I haven't plugged in it yet , the seller said this)
    The radio is a romanian one , model : maestro stereo from 1971 (according to the components)
    http://www.radiomuseum.org/r/electronic_maestro_stereo.html
    It needs 6 fuse slots , but 1 fuse is missing (3 of them are bypassed with wires) .
    So , in the schematic , 1 fuse is drawn using dotted lines (schematic is attached)
    Power supply section is in the bottom right section .
    Is it dotted because you need it if you're using the radio on 110 V ? what happens if it has both fuses inserted ? (i'm using 220V)
    Also , the 4700uf capacitor (C901) is gigant (like an empty toilet paper roll) and the 0,22uf capacitor (C904) looks like an electrolitic capacitor (cylindrical , pink , 0,22uf at 1000V) (it is used for filtering the noise from the ac line , I don't think it's an electrolitic) , can I replace it with a polyester capacitor ? (or something like that)

    Thanks !
    Alternative link for the schematic (full resolution) : https://goo.gl/photos/ETRJw6exPMktshok7
    Image with the front of the radio : http://proradioantic.ro/data/anunturi/1284840645.jpg
     

    Attached Files:

    csxvn likes this.
  2. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    S5 should be inserted for 220V OR S6 for 110V. DO NOT INSERT BOTH.
    C904 is connected across the mains and is not necessary to get the set to work. If suspicious of it just disconnect it. It is there to reduce interference.

    Take out all other fuses and bodge links and measure the voltage across the large electrolytic reservoir capacitor. I would use an isolating transformer and a lamp limiter for safety.

    It would be easier if you posted a small relevent portion of the diagram at a larger magnification.
     
    Richard9025 likes this.
  3. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    Understood !

    I heard that a lamp limiter is just a light bulb connected in series with the ac line ?(And it needs to have the same wattage as the radio , in my case 50w) , but isn't this used for tube sets ? also , what should be the reaction of the light bulb when I plug the radio into the wall socket ? . For example , It should barely light up for half a second and then it shouldn't produce any light (if it works)
     
  4. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Some form of limiter will enable some voltages to be applied without blowing fuses or other components. I use it for tube radios and other devices such as mains motors.
    You can use a bulb with less than 50W since you will not be taking power out till you have found the fault. The quiescent power may be less than 10W.
    The lamp may light a little until the reservoir capacitor has charged up.
     
    Richard9025 likes this.
  5. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    Also , the 4700uf capacitor needs to have the maximum voltage better than 28V ? A 4700uf/35V capacitor will work ?
     
  6. davenn

    davenn Moderator

    14,003
    2,025
    Sep 5, 2009
    That should have read Minimum voltage of 28V

    as long as the rated voltage is the same or higher that what was in there it is good. Be aware that higher voltages will mean that the physical size will be bigger
    so ensure there is room to mount the capacitor

    Dave
     
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