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

Technics 5170 AM/FM Amp
 

"David Corliss" wrote in message
...
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


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.

Technics 5170 AM/FM Amp
 

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

Dave



"Mark D. Zacharias" wrote in message
et...

"David Corliss" wrote in message
...
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


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.

Technics 5170 AM/FM Amp
 

..... much ado about nothing.

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

Thanks again,
Dave


"David Corliss" wrote in message
...
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