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Old 14th March 2013, 01:07 PM   #21
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Quote:
Originally Posted by Mooly View Post
Do we have a circuit for this amp ?

The differential amp transistors will be the first "pair" with the emitters connected (or closely connected) together. Those metal tabbed driver types would be my suspects but none of this is helping is it

Be methodical, and it should take very little time to pin the fault down. Ultimately anything could be causing the problem but in practice it will be one of the "usual" suspects. Old preset pots can go intermittent too, not just the wiper but the rivets that secure the leadouts to the carbon track.
Here we are, service manual
Sony TA-3200F | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
It will be the more recent of the 2 as mine has the protection board included on the amp board and not separate .

Strange thing, when I was checking all those carbon resistors R139 Left Channel and R219 Right Channel both read 0 resistance. How is that possible? should be 4.7
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Old 14th March 2013, 01:12 PM   #22
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Thanks. I found a copy

Any resistors that read different in circuit to the marked value need to be confirmed OK by isolating one end. That normally applies to higher values though. Low value ones usually read correct in circuit so in this case I would guess you might have your meter on a range that can't resolve really low values. You need a "low ohms" range. And the amp must be OFF when measuring resistors in circuit.
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Old 14th March 2013, 01:14 PM   #23
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Originally Posted by Max Headroom View Post
Input diff pair transistors are the usual culprit.
Try swapping these transistors from channel to channel.
While you are at it, inspect these transistors for black legs....this is a usual sure sign of noisy transistors.

Regards, Dan.
THere are a number of the small resistors on the board with blackish legs including thee diff 's.
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Old 14th March 2013, 01:17 PM   #24
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Lots of old parts have black legs.

Stick to a plan for fault finding. Two minutes to swap those transistors around.
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Old 14th March 2013, 01:25 PM   #25
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Originally Posted by Mooly View Post
Lots of old parts have black legs.

Stick to a plan for fault finding. Two minutes to swap those transistors around.
I hear you Mooly.
1. Swap around the suggested transistors. If that works on to...
2. Tans swapped out for lyrics
3. replace those carbon resistors.

Just a note on the tants when I measure the top lead I get 0v and .042v on the bottom lead. Is the 0v lead the neg? I measure .051v on the right channel tant FYI.

Is then the top lead 0v my negative lead.
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Old 14th March 2013, 01:36 PM   #26
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That's it

I'd probably put the carbon comps behind the transistor (the one I don't like the look of)

Measure across the tant to determine polarity. If there is essentially zero volts anyway it can be confusing reading from ground to each end.

What's its reference number on the circuit ?

I'll be back shortly......
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Old 14th March 2013, 01:43 PM   #27
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Originally Posted by Mooly View Post
That's it

I'd probably put the carbon comps behind the transistor (the one I don't like the look of)

Measure across the tant to determine polarity. If there is essentially zero volts anyway it can be confusing reading from ground to each end.

What's its reference number on the circuit ?

I'll be back shortly......
C102 LC and C202 RC - A bit confused by the instructions. I see no polarity on the schematic. DO I measure across the leads with power on?
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Old 14th March 2013, 02:03 PM   #28
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The polarity is in the symbol. The tiny bit (toward the transistor) is positive. You could use a 4.7uf 16 or 25 volt electro as a good replacement here.

If you measure the voltage (which has to be done with it on) then be careful. One slip could cause damage. The voltage across the cap should tally with the polarity but in these applications where there is so little DC voltage anyway across the cap it might conceivably be reverse biased by a few millivolts. Worth checking, and fitting any cap to comply with what is actually measured.
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Old 14th March 2013, 02:35 PM   #29
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Originally Posted by Mooly View Post
The polarity is in the symbol. The tiny bit (toward the transistor) is positive. You could use a 4.7uf 16 or 25 volt electro as a good replacement here.

If you measure the voltage (which has to be done with it on) then be careful. One slip could cause damage. The voltage across the cap should tally with the polarity but in these applications where there is so little DC voltage anyway across the cap it might conceivably be reverse biased by a few millivolts. Worth checking, and fitting any cap to comply with what is actually measured.
Great Mooly, got it on the caps.
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Old 14th March 2013, 04:40 PM   #30
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Well it's not Q101, 103 or 106. What next, do the rest of them in the same way I suppose.
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