?? Old Sony audio power amp , noisy channel

P

Peter Mance

Guest
I've got an old Sony power amp, TAN-7B, that i've had for years.
One channel has gone noisy.

I'm trying to fix it but having a bit of trouble working out which component
is causing the problem.

Its all discrete, FET's, transistors, diodes, capacitors... All the good old
fashioned stuff.
Disconnecting the driver stages from the power stages has eliminated the
power stages.

I've swapped the few capacitors with the corresponding ones from the other
(non-noisy) channel, so its not a cap.

Which components are most likely to go noisy?
Any suggestions for best approach to track such a thing would be
appreciated.

NB. The power rails are clean. so there arent that many options.

Thanks in advance.
 
Peter Mance:
Most usually the source of static like noise is a leaky bi-polar
transistor...... a scope or audio tracer will be of great assistance in
finding the culprit...... also, very briefly touching the soldering iron
to the device in question can make it more or less noisy if it is defective.
Once you have located a suspect you can swap it with the identical
transistor in the good channel. Also you should inspect the solder
connections closely.... look for cracked, cold, or otherwise faulty joints,
particularly near and around the high heat producing components such as low
ohm resistors, diodes and transistors, power transistors and 3 terminal
regulators.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-------------------------


"Peter Mance" <pm@infra.com.au> wrote in message
news:3fcd5192_1@news.iprimus.com.au...
I've got an old Sony power amp, TAN-7B, that i've had for years.
One channel has gone noisy.

I'm trying to fix it but having a bit of trouble working out which
component
is causing the problem.

Its all discrete, FET's, transistors, diodes, capacitors... All the good
old
fashioned stuff.
Disconnecting the driver stages from the power stages has eliminated the
power stages.

I've swapped the few capacitors with the corresponding ones from the other
(non-noisy) channel, so its not a cap.

Which components are most likely to go noisy?
Any suggestions for best approach to track such a thing would be
appreciated.

NB. The power rails are clean. so there arent that many options.

Thanks in advance.
Click to expand...
 
Sometimes freeze-mist used with a pinpoint applicator will help narrow it
down.
You could probably just "shotgun" all the small semi's on that channel at a
reasonable cost.
I have seen dual FET's from Sony's of that vintage cause problems like this.

Mark Z.



--
Please reply only to Group. I regret this is necessary. Viruses and spam
have rendered my regular e-mail address useless.


"Sofie" <sofie@olypen.com> wrote in message
news:vsqp2nkrv7ma47@corp.supernews.com...
Peter Mance:
Most usually the source of static like noise is a leaky bi-polar
transistor...... a scope or audio tracer will be of great assistance in
finding the culprit...... also, very briefly touching the soldering iron
to the device in question can make it more or less noisy if it is
defective.
Once you have located a suspect you can swap it with the identical
transistor in the good channel. Also you should inspect the solder
connections closely.... look for cracked, cold, or otherwise faulty
joints,
particularly near and around the high heat producing components such as
low
ohm resistors, diodes and transistors, power transistors and 3 terminal
regulators.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-------------------------


"Peter Mance" <pm@infra.com.au> wrote in message
news:3fcd5192_1@news.iprimus.com.au...
I've got an old Sony power amp, TAN-7B, that i've had for years.
One channel has gone noisy.

I'm trying to fix it but having a bit of trouble working out which
component
is causing the problem.

Its all discrete, FET's, transistors, diodes, capacitors... All the good
old
fashioned stuff.
Disconnecting the driver stages from the power stages has eliminated the
power stages.

I've swapped the few capacitors with the corresponding ones from the
other
(non-noisy) channel, so its not a cap.

Which components are most likely to go noisy?
Any suggestions for best approach to track such a thing would be
appreciated.

NB. The power rails are clean. so there arent that many options.

Thanks in advance.
Click to expand...
 
"Peter Mance" bravely wrote to "All" (03 Dec 03 13:58:48)
--- on the heady topic of "?? Old Sony audio power amp , noisy channel"

Since you eliminated the power supply to the pre-amp and driver
stage as a source of noise. Perhaps a pre-amp stage bias divider
with a bypass electro which has gone dry? Don't forget resistors can
go noisy too! No effect with the volume control, eh?

If the noise is shot type like popping corn it could be the 1st
preamp transistor after the volume control. Sometimes these may
become damaged over time by the way the circuit behaves when the
power is turned off.

What happens is the transient voltage may apply a reverse bias pulse
to the base-emitter junction during a brief instant. This can cause
the junction to momentarily break down in an avalanche like
behaviour and this does a tiny bit of damage increasing the noise
slightly. But the very slight damage done to the junction is
additive and over a long period of time it may reach a level that
finally becomes obvious.

I repaired a few older amps with this rare problem. The funny thing
is the transistor in the other channel may be just perfect and
completely quiet. Or may simply be a bad internal contact.
Just a few thoughts.


PM> Reply-To: "Peter Mance" <pm@infra.com.au>

PM> I've got an old Sony power amp, TAN-7B, that i've had for years.
PM> One channel has gone noisy.

PM> I'm trying to fix it but having a bit of trouble working out which
PM> component is causing the problem.

PM> Its all discrete, FET's, transistors, diodes, capacitors... All the
PM> good old fashioned stuff.
PM> Disconnecting the driver stages from the power stages has eliminated
PM> the power stages.

PM> I've swapped the few capacitors with the corresponding ones from the
PM> other (non-noisy) channel, so its not a cap.

PM> Which components are most likely to go noisy?
PM> Any suggestions for best approach to track such a thing would be
PM> appreciated.

PM> NB. The power rails are clean. so there arent that many options.

PM> Thanks in advance.

.... Which sparks some mnemonic circuitry.
 
Thanks for the suggestions, it does have a dual FET in the input stage, i'll
check that chap next.

I'd already resoldered just about everything in site (dodgy or not).

"Mark D. Zacharias" <mzacharias@yis.us> wrote in message
news:bqkgr5$22hb5r$1@ID-180484.news.uni-berlin.de...
Sometimes freeze-mist used with a pinpoint applicator will help narrow it
down.
You could probably just "shotgun" all the small semi's on that channel at
a
reasonable cost.
I have seen dual FET's from Sony's of that vintage cause problems like
this.

Mark Z.



--
Please reply only to Group. I regret this is necessary. Viruses and spam
have rendered my regular e-mail address useless.


"Sofie" <sofie@olypen.com> wrote in message
news:vsqp2nkrv7ma47@corp.supernews.com...
Peter Mance:
Most usually the source of static like noise is a leaky bi-polar
transistor...... a scope or audio tracer will be of great assistance in
finding the culprit...... also, very briefly touching the soldering
iron
to the device in question can make it more or less noisy if it is
defective.
Once you have located a suspect you can swap it with the identical
transistor in the good channel. Also you should inspect the solder
connections closely.... look for cracked, cold, or otherwise faulty
joints,
particularly near and around the high heat producing components such as
low
ohm resistors, diodes and transistors, power transistors and 3 terminal
regulators.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-------------------------


"Peter Mance" <pm@infra.com.au> wrote in message
news:3fcd5192_1@news.iprimus.com.au...
I've got an old Sony power amp, TAN-7B, that i've had for years.
One channel has gone noisy.

I'm trying to fix it but having a bit of trouble working out which
component
is causing the problem.

Its all discrete, FET's, transistors, diodes, capacitors... All the
good
old
fashioned stuff.
Disconnecting the driver stages from the power stages has eliminated
the
power stages.

I've swapped the few capacitors with the corresponding ones from the
other
(non-noisy) channel, so its not a cap.

Which components are most likely to go noisy?
Any suggestions for best approach to track such a thing would be
appreciated.

NB. The power rails are clean. so there arent that many options.

Thanks in advance.
Click to expand...
 
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