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undefinedza 6th October 2012 02:13 PM

Precision Acoustix 250
 
2 Attachment(s)
Hi everyone,

I have the opportunity to buy two Precision Acoustix 250 monoblocks.

They were built locally in South Africa, and very, very little information is available about them.

One of the monoblocks distorts slightly (unfortunately the seller is in another town, so I can't listen), and the seller claims that a resistors looks slightly blackened.

The price seems pretty good, but before I commit to buying, I'd like to get some input on fixing it.

I have attached the two pictures he has provided. I have asked for a close up of the main PCBs and will post them once I receive...

Any comments on the design, repair, potential specifications, etc would be much appreciated.

Thanks,
Chris

undefinedza 6th October 2012 02:22 PM

2 Attachment(s)
Close ups of the main PCBs attached.

What kind of design is used? Specifications?

How easy would it be to diagnose and solve this problem?

Thanks guys.

sreten 6th October 2012 03:23 PM

Hi,

Complementary paired Mosfet output stage.
Around 150W or so 8 ohm, 200W or so 4 ohm.

You might be able to fix it by comparing the two channels and swapping components.

rgds, sreten.

undefinedza 6th October 2012 03:25 PM

Hi streten,

Thanks for the response!

I'm hoping that the fix is easy.

I think I'm going to pull the trigger on this :)

Cheers,
Chris

rudi 6th October 2012 09:14 PM

they will be easy to fix. I have the circuit diagram for you and can also show you how to mod them to sound much better.

you can buy them with confidence.

undefinedza 6th October 2012 09:20 PM

Quote:

Originally Posted by rudi (Post 3192132)
they will be easy to fix. I have the circuit diagram for you and can also show you how to mod them to sound much better.

you can buy them with confidence.

Thanks Rudi!

Much appreciated :) I'll chat to you soon.

Chris

undefinedza 10th December 2012 12:21 PM

Hi all,
I'm still struggling with these.

I've replaced all of the small signal transistors (BC546 and BC556) on the left and side of the board, as well as the input stage transistors (is that correct?) which are BF470 and BF469.

No luck. Same distortion. I've looked at one monoblock vs another and they look identical. The only difference is the output MOSFETS, which seem to have been replaced on the new monoblock. The current output MOSFETS test fine.

Any ideas?

Cheers,
Chris

undefinedza 10th December 2012 12:48 PM

Tried using the MOSFETs from the working amp in the broken one... no luck.

east electronics 10th December 2012 01:10 PM

Quote:

Originally Posted by undefinedza (Post 3278596)
Tried using the MOSFETs from the working amp in the broken one... no luck.


obviously .... replacing outputs that already work from one amplifier to another will not change anything ...... transistors is like a car wheel either working or not

keep the transistors as was ...check soldering recap the all unit ....

expect any of the small transistors to have some small leak
but 99% of the cases is some of the small capacitors doing the trick


Kind regards
sakis

undefinedza 10th December 2012 01:45 PM

Electrolytics first?


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