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Transformer's terminals according to the schematic

Discussion in 'General Electronics Discussion' started by Richard9025, Apr 17, 2017.

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  1. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    Hi !
    Someone messed the wiring in the power supply section of this radio and I can't figure out what terminal of the transformer is what point in the schematic :
    Schematic with the transformer and info :
    transformer.jpg
    Schematic with the whole power supply :
    mini.jpg
    The actual transformer
    DSCN0001.JPG
    DSCN0003.JPG


    So can you tell what terminal is what ? there are 6 terminals on each side , the pink cylindrical thing is the 0,22uf 1000V across-the-line capacitor , or do I have to sherlock this thing out ? (most of the wires in the power supply's section are cut , the rest of the radio is ok)
    Also , what is L6 ?
    Thanks !
     
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Nice pictures.

    L6 looks to be a winding connected at one end only to act as an interference screen between primary and secondary. It should be connected to the core. This will give an indication of the order of the primary connections.

    C904 is shown as connected to one end of the primary but in practice looks to be connected in the middle. To resolve the issues, I would put in a low AC voltage into one winding and measure the volts on the other windings.
     
    Richard9025 likes this.
  3. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    IMG_0003 - Copy.jpg
    Brown line = connection from terminal to the windings
    No wonder why the radio wasn't working !
    The other wire of the 220V ~ goes to a fuse then .. nowhere , someone cut the wires , almost all of them (in the power supply's section .
    Now , I want to rewire all of them but I need to know which point on the drawing (1-12) corresponds to the points on the drawing (a1,b1 ... a5,b5) .
    But almost all of the wires are desoldered , I hope the drawing up above can predict the order of the points .
    Also , "but in practice looks to be connected in the middle" :
    `.JPG
    This may explain the construction of the transformer

    I would need a DC-AC converter or an autotransformer to do that , I don't have one of these.
     
  4. Bluejets

    Bluejets

    4,227
    897
    Oct 5, 2014
    Need the rest of the drawing.
     
  5. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    The primary consists of two windings connected in series. These have the same number of turns but a different wire diameter. The lowest resistance winding will be the 110V winding and the higher resistance winding will be for 220V.

    Al the secondary windings are two terminals only and the voltages can be measured when the transformer is energised. These windings can be connected either way round.

    All my testing is done with a 30mA earth leakage circuit breaker for safety.
    Use a lamp limiter for the first energising and then bypass the lamp for a long term temperature test.

    Some wall warts have low voltage AC output or you could steal a low voltage AC output from another amplifier.

    If things look good, connect the 6.3V winding to C902 and you should get dial lights.
     
    Richard9025 likes this.
  6. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    Umm... Almost all the wires are cut , what you see in the drawing is what is connected to the transformer , to rewire all the wires I need to know which terminal of the transformer is which point in the schematic ...

    I'll do some continuity and resistance tests between the points

    I'll do that when I rewired the power supply section

    So , I searched on the internet the transformer and I found something

    ----------------------------------------------------------------------------------------
    L1+L2=primary=455windings/0,4mm +455sp/0,25mm for 220 V AC

    L3=secondary 1=88windings/1,0mm; for audio amplifier - 20 V AC

    L4=secondary 2=28windings/0,65mm; 6,5 V AC for dial lights

    L5=secondary 3=66windings/0,5mm; 15 V AC for RF and IF

    L6=screen =350windings/0,1mm
    -----------------------------------------------------------------------------------------------


    Also , I found a transformer schematic of ANOTHER RADIO but it is very similar :

    BUCUR TRANSFORMER.jpg

    See that cell in the spreadsheet with : R(Ω) ±10% ? (top left) , I can measure the resistance and I'll post here the results
    NOTE : This isnt the EXACT TRANSFORMER , it is something similar !




    These are the current terminals of my radio's transformer :
    maestro stereo transformer.jpg


    I need to know which terminal (1-12) is which point , you can see that some terminals are blank , like 3 and 10 and 7

    Resistance and continuity tests incoming !
     
  7. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    RESISTANCE.jpg

    The values are approximate , my multimeter is crappy

    Continuity is between 1-2 , 4-5-6 , 8-9 and 11-12
    The dial lights are connected to 11 and 12 (the wires are the same color , they have been cut of course)
    4-6 has bigger resistance than 5-6 so :

    11-12 must be L4
    4-6 must be L1+L2
    1-2 is L5 ?
    8-9 is L3?

    Check these assumptions using data that I provided above
    Anyways I could put 220 through 4-6 and then check the AC voltages between 11-12 , 1-2 and 8-9 ;)

    Thanks !
     
  8. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Do not connect the secondaries until you have the primary running with no faults.
    Measure the secondary voltages to determine where the secondaries are to be connected.
    Go gently, bit by bit.

    Looking at a different transformer is only going to confuse you.
     
    Richard9025 likes this.
  9. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    Got some gloves , a suicide cord and a circuit breaker , I'll disconnect all the wires of the transformer then I'll solder the live wires to 4 and 6 and then , when I hooked them up , I'll measure the voltages across 1-2 , 8-9 and 11-12 .
    DSCN0026.JPG
     
  10. Richard9025

    Richard9025

    205
    7
    May 24, 2016
    After 45 years , the transformer works great !
    transformer.JPG
    One last small question before I can consider this thread closed :
    Why are this new capacitors like ten times smaller than those from 1972 :
    DSCN0038.JPG
    DSCN0030.JPG
    Actually the newer 4700 uf cap is much smaller than in the image , I held it close to the camera .
    Thanks duke for your much appreciated help !
     
  11. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    You are welcome, I enjoy helping people it gives me much satisfaction.:)
     
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