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Ev p 3000 power amp fault
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    Posted: 28 May 2011 at 2:05pm
gonna give this ev a rest for the weekend and start a fresh next week...will get it to work correctly Smile
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will warm up the scope later and recheck the sine wave at the o/p's of both channels..
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just having a break from it at the moment....as it's driving me round the bend...
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will re look into that and disconnect to cable and check o/p end...
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Originally posted by ceharden ceharden wrote:

Also, does the output from the two channels look the same on the scope, same clipping points under load etc?  The current limiting circuits could potentially cause oddities like this too.


What does the output signal look like on the 'scope?
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The other fault I've seen which can cause some odd things to happen are the thermistors on the output board going intermittently open circuit.
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Incidentally, the DC offset adjustment is purely for the VCA which does the limiting.  There is no offset adjustment for the output stage itself.

Also, does the offset stay the same whether there is a load on the output or not?

As I said before, your investigation has to centre around why the servo isn't able to correct the offset.  Eg, for starters, is the DC offset present on the input of the integrator and what is the integrator outputting?
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What happens if you disconnect the ribbon cable going to the output board.  Is there still a DC offset?
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Thanks for talking...now you can see how it's acting up...

new pcb more like for this old timer....more testing to be done here...I will post the out come...gin..
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Don't rely on the protection circuits for fault diagnosis.  The VHF sensing part is quite insensitive, you need to have a pretty large oscillation before it'll put the amp into protect.

I think watching the behaviour of the amp running into a load might give you some clues.

The P series has a DC servo to correct for any offset so there must be some reason why it is unable to detect and correct for it.
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@audiomlk, there's no oscillation at the o/p of this unit as it protect's it's self and will pull the o/p relay off...

@ceharden I will be scoping the o/p and see what happens, it's case of looking at it to long and going round the house's as they say...the current limiter as been rebuild in the o/p stage aswel..
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Also, does the output from the two channels look the same on the scope, same clipping points under load etc?  The current limiting circuits could potentially cause oddities like this too.
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