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Quasar gx36005yq boombox

Discussion in 'Troubleshooting and Repair' started by Electric-T, May 16, 2018.

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  1. Electric-T


    Jun 4, 2017
    Trying to bring some life back to this radio.
    First off, this was my journeymans radio until today when it fried. We had wired up a few temporary receptacles for tools and tunes. Well, apparently we "lost the neutral" this afternoon. Since the recep was a leg off of a 480 3ph supply, when the neurtal came disconnected, the once 115v circuit was now supplying 187v. It fried it. He said i could take it and try and fix it so i did.
    I cant find a schematic and visually nothing looks burnt or exploded. When i tested the AC pwr in jack i got 120v. It then goes to a transformer where its stepped down and rectified to a voltage i can only assume is 7.5v (I assume this because it also be powered with 5 D batteries which the radio says is 7.5v.)
    On the other side of the transformer i get no reading ac or dc.
    I have 3 questions
    1. Am i right in coming to the conclusion that the transformer is burned up?
    2. Assuming 7.5v is the output could i get any transformer within the specs to replace it?
    3. Is there any way to find out exactly how many amps the radio pulls on the dc end?
    The power specs are AC 120v 60hz 11W but i dont know if thats true after the transformer
  2. dave9


    Mar 5, 2017
    You are measuring the output (secondary) of the transformer, not after the rectification stage, correct?

    Have you measured the resistance of the secondary and/or primary windings? If they are completely open circuit you can be sure one has a problem but a resistance might also come from somewhere else in the circuit so it could be good to pull the transformer out of circuit.

    I would find an alternate source of 7.5VDC, whether a bench supply or 5 x D cells or whatever, to see if the rest of the radio still works... no point in replacing the transformer if something down-wind of it also fried.

    Anyway, yes you could get a replacement transformer if that's all that is wrong, but you might find it tricky to mount in the available space - or maybe not, some boom boxes used rarer transformers than others and the specific dimensions were held in with molded plastic partitioning - which you may or may not be able to modify if present.

    Anyway, not a high power amp with only 7.5V input. I'd shoot for a 1 amp transformer, OR put a DC barrel socket on the housing and power it with an AC-DC PSU which commonly has a DC barrel plug on it, then you don't need any of the PSU circuitry, can wire it directly to the output from the bridge rectifier, but in case the diode(s) are blown you might just pull them out if you do this.

    It might not hurt to post pictures of anything that seems relevant if the above wasn't enough to get you started.
  3. Electric-T


    Jun 4, 2017
    Thanks. I did have the thought to try strait dc power. I will post some pictures of it when i get home tonight. This will get me off to a good start
  4. kellys_eye


    Jun 25, 2010
    The voltage at the primary may well be on the terminals but not at the actual winding - there is often a thermal fuse fitted (physically) within the covering of the primary winding - look for a 'bulge' in the covering and you might be able to carefully cut the tape away to reveal this fuse and fit a replacement.
  5. Electric-T


    Jun 4, 2017
    Thanks. Ill look at it again when im home. Its super old and it would be pretty cool to get it working again
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