Hi everyone. Nice to talk to you all. just registered here. I'm working on a Clairtone 7980 and the lower deck motor voltage is approx. 15vdc instead of 12. that might be why the first motor basically melted. Anyone had this problem before?
Clairtone 7980 lower deck motor voltage
- Thread starter area51
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caution
Member (SA)
The lower deck's motor can take 8.4-15V. There'a a 33-ohm dropping resistor for it at R343, which, if the motor truly draws 72mA like the datasheet says, will drop it by 2.4V. That means you can't exceed 17.4V without exceeding 15V to the motor. But uh oh, the AC rectifiers on these put out 18-20V!
The reality of it is, R343 is never a 33-ohm resistor; that's only what the schematic says. What they really installed is a pair of zener diodes in series. I don't know what the zener voltage rating is and I haven't measured that spot, but I'm guessing it's very similar on batteries as it is plugged in. If those diodes fail and short out, the motor's going to get more than 15V when using a cord, which might damage it.
The reality of it is, R343 is never a 33-ohm resistor; that's only what the schematic says. What they really installed is a pair of zener diodes in series. I don't know what the zener voltage rating is and I haven't measured that spot, but I'm guessing it's very similar on batteries as it is plugged in. If those diodes fail and short out, the motor's going to get more than 15V when using a cord, which might damage it.
That's great info thanks! I guess im back to the drawing board on the lower deck playing and sounding like the Chipmunks
baddboybill
Boomus Fidelis
There is an adjustment for motor speed and if it’s not working then the motor should be replaced!!! And FYI the resistor Caution (Eric) is speaking of, tends to need replacement if never done
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Ok thanks' Mine has the 2 zener diodes in series in place of that, and they seem to check out ok.
BoomboxLover48
Boomus Fidelis
Chipmonks sound can be made by a slippery pinch roller also, besides dirty record switches.
~Royce
~Royce
Radio raheem
Requiem Æternam
I have seen this before on other boxes....if there is an adjustable pot on the board linked to the motor, chances are that will need replacing, a real common issue on jumbo boxes
Hi Haven't posted in a while, but working on that same Clairtone again. still sounds like chipmunks even with the motor voltage adjusted to minimum.I get 15.15vdc at the motor and before r343 (2 zener diodes) i get 16 5v. Stumped
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