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DIY For Audio
General Tips on Stereo Receiver/Amplifier Restoration
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<blockquote data-quote="Family_Dog" data-source="post: 1086776" data-attributes="member: 82"><p>I think you've covered most things applicable, there are other things that could go wrong as well. I battled many hours with a Technics SE-5 that would work for anything from 30 minutes to 30 hours and then go into protection. I figured the protection IC was faulty because the all voltages around it at the time of measurement were all correct. The bias was correct. I had replaced all the relevant electrolytic caps. The problem persisted. I then started checking each of the little transistors involved in the power regulation/supply circuits - luckily not surface mount - by removing them and checking them out of circuit. Interestingly, I found one transistor that was completely the wrong polarity (NPN instead of PNP - or the other way round, I don't remember now) - and yet the set still worked. I thought I had found the fault, yet I had not. So then I turned to the components other than transistors around the speaker protection circuit, and replaced a very healthy looking diode. The diode did not measure faulty or leaky at all, but it was the guilty part. Replacement with a new diode cured the problem and the amplifier has played faultlessly since. </p><p></p><p>You should also be aware of any part of the circuit heating up abnormally.</p><p></p><p></p><p>-F_D</p></blockquote><p></p>
[QUOTE="Family_Dog, post: 1086776, member: 82"] I think you've covered most things applicable, there are other things that could go wrong as well. I battled many hours with a Technics SE-5 that would work for anything from 30 minutes to 30 hours and then go into protection. I figured the protection IC was faulty because the all voltages around it at the time of measurement were all correct. The bias was correct. I had replaced all the relevant electrolytic caps. The problem persisted. I then started checking each of the little transistors involved in the power regulation/supply circuits - luckily not surface mount - by removing them and checking them out of circuit. Interestingly, I found one transistor that was completely the wrong polarity (NPN instead of PNP - or the other way round, I don't remember now) - and yet the set still worked. I thought I had found the fault, yet I had not. So then I turned to the components other than transistors around the speaker protection circuit, and replaced a very healthy looking diode. The diode did not measure faulty or leaky at all, but it was the guilty part. Replacement with a new diode cured the problem and the amplifier has played faultlessly since. You should also be aware of any part of the circuit heating up abnormally. -F_D [/QUOTE]
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DIY & Tutorials
DIY For Audio
General Tips on Stereo Receiver/Amplifier Restoration
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