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Technics 5170 AM/FM Amp

Problem is that the 3 amp speaker fuses are blowing, also have poor audio signal on one channel.

So far have done basic check on power transistors ... checked out okay but hfe was only 20 or so. They are original parts ... maybe 25 years old.

Checked most of electrolytic caps in power section ... replaced one.

Replaced most, but not all of 'support transistors' in power section ... was able to get a weak audio signal from one channel. However, raising the volume level blew a speaker fuse.

The question now is whether to spend $40 on new power output transistors (total of 4 ... 2SD586). Specifically, could the existing output power transistors check out okay, with no obvious shorts, but still not produce the rated signal power level ... and also cause a speaker fuse to blow?

Thanks ... Dave

Reply to
David Corliss
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You appear to have a DC offset being passed from the amp channel to the speaker, or a (nearly) shorted speaker. Try carefully pushing the woofer in about 1/4 to 1/2 inch and releasing it. If there's a scraping, crusty feel, the woofer is damaged. A woofer in this condition can in turn damage the amplifier. Most newer and especially larger reveivers and amps have protection circuits to help prevent this type of thing.

Mark Z.

Reply to
Mark D. Zacharias

..... I need to check the DC offset at the speakers. Thanks for the suggestion.

Dave

Reply to
David Corliss

.... much ado about nothing.

Problem appears to have been defective external speakers, rather than a problem internal to the 5170.

Thanks again, Dave

Reply to
David Corliss

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