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Old Electronics
Turntable Cosmo B3210 does not turn the engine
265
hace 5 años
hace 5 años
Hello, I have a Cosmo B3210 which after changing the capsule and working well, suddenly the engine has stopped turning overnight, I have disassembled it and from the power transformer there are two cables that feed a plate with 12v, I suppose which will be the engine speed regulator, from that insert two other blue and red wires are connected to the engine, a red wire from the motor housing goes to the positive 12v, and another wire that is connected to the screw of the Metal plate where the motor is screwed is also connected to 12v, apparently there is a short of this last cable since between this and the negative it gives me 10v, it seems that there is a current leakage of a piece that looks like a cylindrical transistor which in turn goes into a heatsink.
If I disconnect the cable from the screw cable, the motor rotates perfectly with the appropriate revolutions and the turntable works well. I would like to know what function the two cables have, the one that is connected to the motor housing and the one that goes to the metal plate screw, and the type of transistor it carries, attached photos.
Transistor Photo
https://image.ibb.co/hxUOxK/IMG_20180907_170038.jpg
Photos of the plate and the motor
https://image.ibb.co/fUVYXK/Foto_placa_motor.jpg
https://image.ibb.co/kEuMKz/Foto_editada_motor.jpg
10.397
hace 5 años
hace 5 años
If the motor is 9v and the power is 12v, the plate must be in charge of lowering the voltage, as you say it is a voltage regulator plate, it measures the transistor that may be short, this transistor is Germanium, very difficult to get today if you are looking for the originality of the device you will have to get it, if you don't mind that you can put a 9v, 1A silicon regulator in place of the whole board, these regulators bring 3 legs and are very economical, the cables connected to The housing can be mass to attenuate engine noise, greetings ,,
265
hace 5 años
Thanks for answering pr122, I have researched and as you say I think it is a Germanium transistor, the problem is that the reference is not seen, everything is deleted, although I think it could be an OC74 Germanium PN74 that can still be found, I have unscrewed and removed from the heatsink the transistor and now it works well, I try it for a short time because without the heatsink it heats up a bit.
Regarding the other question, I don't know what function the two wires that are connected to the positive + 12v have, the red wire screwed to the motor housing and the other screwed to the metal plate.
10.397
hace 5 años
hello as I told you they must be mass, to attenuate noise, I kept in mind that not every time mass is negative, in old devices, the mass was always positive, because they used PNP transistors, the motor noises were coming from the collector, thin, they produce voltaic arc with the coals, this generates annoying noises, more than anything in old engines with little antiparasitic technology, today it is something else, and it has improved a lot in this aspect, as for the transistor I do not think it is an OC74 , these were longer, it seems to be one of the AC line greetings
10.397
hace 5 años
could be AC127 or AC128 according to the PNP or NPN polarity, you could try some silicon in that place when working as a regulator, I do not think there are problems, try to be at least 1 Amp like the BC337, or BC327 always of according to the polarity of the original, greetings
265
hace 5 años
Thanks again, indeed those cables are to prevent hum, after some inquiries, I have discovered that this transistor is an AC188 that has the AC128 and AC 153 as a replacement, and in the OC74 datasheet it appears to me that it has the AC128 as a replacement , AC153 and AC188.
Greetings
10.397
hace 5 años
Always check the voltage and amperage of the transistor's work, many times they give you as a replacement for another transistor with a higher working regime, this is fine, what they do not say is that the reverse should not be replaced because you would be putting a transistor more boy and would have to endure the work regime of the original, this does not hold and burn, greetings
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