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Old 15th January 2013, 11:30 AM   #1
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Default Sony TA-AX3, two problems

Hi folks,

I have a Sony TA-AX3 with 2 problems.

One is noise I believe due to dirty switches and that's easy to fix.

But the other is that when I put the Bass control to the MAX level it stops working. When I put it back to the flat point it plays back again normally. It doesn't happen with Treble control. Is it any relay going in protection mode?

Some component out of specs? Pictures attached.

Thanks a lot.
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Last edited by Karl vd Berg; 15th January 2013 at 11:33 AM.
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Old 15th January 2013, 01:55 PM   #2
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Noise is most likely to be leaking capasitors.

Remember that when you put the bass-control fully clockwise, the power output in the bassregion is several times higher than the rest of the frequency range.
If the range of the bass control is around 12dB, the power output will be 16 times higher than the rest of the range. Given You have some subsonics too, the power will even go higher. Some depends on how the tone controls are made.
I guess it is the speaker-protection relay that makes the amp quit working?
All sound gone?
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Old 15th January 2013, 03:10 PM   #3
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Quote:
Originally Posted by TANDBERGEREN View Post
Noise is most likely to be leaking capasitors.

Remember that when you put the bass-control fully clockwise, the power output in the bassregion is several times higher than the rest of the frequency range.
If the range of the bass control is around 12dB, the power output will be 16 times higher than the rest of the range. Given You have some subsonics too, the power will even go higher. Some depends on how the tone controls are made.
I guess it is the speaker-protection relay that makes the amp quit working?
All sound gone?
Yes, all sound go only when I turn the bass control clockwise... Subsonics are off. When it is back to flat position, I hear a "click" and the sound is back...

Shouldn't be like this, should it?
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Old 15th January 2013, 05:21 PM   #4
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Should or should not.
Well that depends on where the volume is set.
Try this next time: Turn the bass clockwise until the relay "pops" and then turn it back to about three o'clock. Wait a second or two, and the relay will most likely to klick in again.
You can also try when the subsonic is ON.

Also fault on the bass pot can make this alone.
If the track is broken inside the potmeter (Happans some times) then the tone control in total may swing and send out even white noise in levels way beyound the triggerlevel for the speaer protection. Often seen in vintage equipment.
Have you tried to clean the pots yet?
Use a good lubricating electronic cleaner.
Avoid those who are based on petroleum. They will damage any nylon parts inside.
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Old 16th January 2013, 12:44 AM   #5
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Quote:
Originally Posted by TANDBERGEREN View Post

Also fault on the bass pot can make this alone.
If the bass pot is breaking the circuit then it could be upsetting dc conditions and the op-amp is going to one rail or the other.

First thing to do is either clean the pot or replace it.
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Old 16th January 2013, 03:14 AM   #6
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Cracking sound is a sign of damaged/opened solder points.

How come there is only one big capacitor...or is it dual

Gajanan Phadte

Last edited by gmphadte; 16th January 2013 at 03:19 AM. Reason: added content
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Old 16th January 2013, 12:31 PM   #7
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Single powersupply and outputs either brigded or with an output capacitor (The two a bit larger ones near the power module) I'll check whats for real.

A bit strange this one.
Depending of model there is two or four 220uF 50V caps in the power. Assisted by four inductors to smooth the rails.
The big one next to the rectifier diodes is a 330uF 400V capacitor, wich is switched in via a relay after the amplifier has been started up.
And there they were. Two 1000uF 50V capacitors, the3 two ones near the powerblock.
But the relay isn't in the schematics, just on the drawings of the boards, likewise with the large cap near the rectifiers.
Must STILL look a bit more what they have done here.

Aha. The power is a SMPS. Thats why the 300uF 400V is there.
The schematics I have available is close to be unreadable in the powesupply areas.
Then the capacitors doesn't need to be as big either.
Explains a lot actually.

OCL-outputs with a +/-40V rail to the powerblock, giving 40 + 40 Watts output.

Want the schematics? Or do You have a copy yet?
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Last edited by TANDBERGEREN; 16th January 2013 at 12:56 PM.
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Old 16th January 2013, 01:09 PM   #8
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The bass pot was completely opened and cleaned, de-oxided. I put it back and still it cuts the whole sound when I turn the bass control clockwise...



Yes, the schematics would be great. Maybe the Bias control are over limits and need to be re-adjusted??? I only need to know where can measure it (Bias/DC offset)...
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Old 16th January 2013, 07:59 PM   #9
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Quote:
Originally Posted by TANDBERGEREN View Post
Want the schematics? Or do You have a copy yet?
Tandbergeren, do you still have that schematics?
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Old 16th January 2013, 08:27 PM   #10
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PM me your Emailaddress, and you will have it in minutes.

BTW.
No biasadjustment in this amp.
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Last edited by TANDBERGEREN; 16th January 2013 at 08:33 PM.
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