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KEF PSW-2500 Subwoofer
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tux
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PostPosted: Tue Jun 20, 2006 8:04 am    Post subject: KEF PSW-2500 Subwoofer Reply with quote

Hi

Common problem with these subs is the power supply/amp board. So if anyone has repair experience or schematic please help.

Thank you

Cheers
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tux



Joined: 20 Jun 2006
Posts: 5

PostPosted: Tue Jun 20, 2006 8:09 am    Post subject: Re: KEF PSW-2500 Subwoofer Reply with quote

tux wrote:
Hi

Common problem with these subs is the power supply/amp board. So if anyone has repair experience or schematic please help.

Thank you

Cheers


Just to add that I have registered in the forum as tux.....
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PostPosted: Tue Jun 20, 2006 6:41 pm    Post subject: Reply with quote

Do all of the powersupplies test within specifications? What do the outputs test like?
Maybe you could follow the signal through the stages with a tiny speaker?
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tux



Joined: 20 Jun 2006
Posts: 5

PostPosted: Wed Jun 21, 2006 5:31 am    Post subject: Reply with quote

Anonymous wrote:
Do all of the powersupplies test within specifications? What do the outputs test like?
Maybe you could follow the signal through the stages with a tiny speaker?


Hi

Thanks for the reply m8.

I have checked power supply section of board and get a reading of +50V and -50V. Also the +15V and -15V are OK. Signal measured into the power amp section from pre-amp board is ok. ( Measured with scope ).

Problem is the relay is not turning on. This is controled by the TA7317P, and without a schematic and lack of experience in this amp I don´t know where the control signals for the protection are coming from.

Best Regards

Cheers
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PostPosted: Wed Jun 21, 2006 6:22 pm    Post subject: Reply with quote

What does the supply at the TA7317 scope like? I guess you have checked all of the solderjoints. I can't help you with a schematic.

Let us know what you find. Smile
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tux



Joined: 20 Jun 2006
Posts: 5

PostPosted: Thu Jun 22, 2006 12:02 pm    Post subject: Reply with quote

Anonymous wrote:
What does the supply at the TA7317 scope like? I guess you have checked all of the solderjoints. I can't help you with a schematic.

Let us know what you find. Smile


Anonymous wrote:
What does the supply at the TA7317 scope like? I guess you have checked all of the solderjoints. I can't help you with a schematic.

Let us know what you find. Smile


Hi

Haven't used the scope on the TA7317 as i don't know what to look for Confused .
I bypassed the protection circuit relay and the amp works for about 20 minutes then outputs 50Vdc on the speaker terminals.
The power transistores don't get hot and they tested OK, so shouldn't be these.
There are some 5 and 2 watt resistors around the power supply section that get VERY hot, even when on stanby. Is this normal ?

Thanks in advance for any clues as to what may be causing the DC voltage on the speaker terminals.

Cheers
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PostPosted: Fri Jun 23, 2006 11:57 pm    Post subject: Reply with quote

I mean scope the power in to the 7317, to make sure it is normal. DC on the outputs after some time...That would cause the protection to operate..... I would be changing silicon devices.......What else could break down like that. What are the resistors/capacitors like between the stages?
What does the power out test like when this happens? I don't know if this is normal.
What is the waveshape like into the outputs when this happens?

let us know. Smile
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Electronicswiz
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PostPosted: Fri Jul 07, 2006 5:15 am    Post subject: KEF PSW-2500 Reply with quote

My kef psw 2500 has just stopped working to. I have had to replace the rectifier and a BD140 transistor. Sadly this has not solved the problem compleatly. I have scoped a lot of it, but sadly in the process of scoping it I stupidly managed to blow up a bit more of it!!!!!!!!!! ooooops! I am about to try and draw up a circuit diagram of it so i can see exactly what is going on. Have you managed to solve the problem with yours?
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bigfathairybiker



Joined: 06 Jul 2006
Posts: 2
Location: Cambridge, UK

PostPosted: Fri Jul 07, 2006 6:26 am    Post subject: Reply with quote

Hi,

Ok, dc on the output!
Q: Is the output Class A, B or whatever or is it Class D?

Check the output capacitor/s.
If class D then it will very likely be the output caps or the toroid open circuit.

Just some ideas.

Mark
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PostPosted: Sun Feb 18, 2007 3:22 pm    Post subject: Reply with quote

I had one of these with similar problems; there is a single 1N4006 fed off one of the transformer secondaries and provides a supply to the relay coil. This half wave rectified supply is smoothed by a single 100uf electrolytic. This had gone dry and the relay wouldn't energise until I replaced the duff cap.

After this, all was well. It looks like the cap had been 'cooked' by a coulpe of underspecified resistors nearby.

Hope this helps someone...
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