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max807
Apprentece
6 Posts |
 Posted - Jul 09 2007 : 2:23:03 PM
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Hi. I'm trying to find out what's wrong with my multitrack cassette recorder. The cassette motor and mechanism works, but the power light and LEDs and all other functions are out. There is no fuse on the circuit board, but I was able to spot a transistor which is badly chipped on one side, so that the copper inside is showing through. Unfortunately I don't have any testing equipment to hand.
Circled in red in this pic:
http://xs.to/xs.php?h=xs217&d=07281&f=transistor.jpg
Is it possible, that this transistor is to blame for why the unit doesn't work? Would this kind of damage be enough to kill a transistor? Thanks |
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tim
Mad Scientist
198 Posts |
Posted - Jul 11 2007 : 08:32:08 AM
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| of course a transistor showing copper is bad but you have to look at other conponets . diodes that reversed polarity in the power supply section, i would start there but befor doing anything try to get a number of that transistor first. |
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max807
Apprentece
6 Posts |
Posted - Jul 11 2007 : 2:42:46 PM
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Yes thanks Tim for your input. I agree it's not looking good for that transistor. On Usenet I found out that the transistor has actually exploded.
I am curious about what you're saying about diodes reversing polarity. Is it possible for a diode to change direction like that?
Also, I have a couple of very domed capacitors in the vicinity of the power input. Could this be a cause? |
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tim
Mad Scientist
198 Posts |
Posted - Jul 11 2007 : 3:23:48 PM
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| hi, does this unit plug into an outlet? if so then if i were you i would go from the power supply in from there. and yes diodes will change direction and can reak havak on other conponents, ive had similer problems with an inverter where a diode reversed polarity and burned up several transistors and a few caps. |
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cyclopsitis
Nobel Prize Winner
Canada
732 Posts |
Posted - Jul 11 2007 : 9:13:46 PM
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I've had some nasty diodes do that to me too! I had one blow up in my face once! After that I always ware safety glases when soldering or checking a powered circuit.
K |
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max807
Apprentece
6 Posts |
Posted - Jul 13 2007 : 08:26:48 AM
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| Thanks for the help guys. This is looking like a much bigger repair job than I initially expected. Thanks to the suggestions I received over the internet here and elsewhere, I know where to start. |
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SamRadford
Apprentece
United Kingdom
10 Posts |
Posted - Jul 21 2007 : 06:46:08 AM
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For the record, diodes don't "reverse polarity". They just go short-circuit.
(56 year old electronics engineer).
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cyclopsitis
Nobel Prize Winner
Canada
732 Posts |
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Is this a dead transistor
