Help-Acurus A-250 amp repair advice needed - long. - diyAudio
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Old 7th April 2009, 03:49 PM   #1
hafp is offline hafp  United States
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Default Help-Acurus A-250 amp repair advice needed - long.

Hello,

Was doing basically some parts swapping mods to an Acurus A-250 amplifier and have run into problems.
These mods were done in stages as suggested by members on the threads here.

I have the schematics for the amp; which includes the power supplies and the amp circuits.

The first mod was done to the power supply; changed from the single bridge rectifiers to twin bridge rectifiers along with four new filter caps and bleed resistors.
This amp uses a single 1000va 80v toroidal transformer with the filter caps wired in series and feeding the two amplifier board circuits.
The +/- VDC outputs from the power supply filter caps to the amp boards is 45V.
This mod was completed with no problems and improved the sound a bunch.

Next mod was to change the 1N5408 diodes to Fairchild Stealths, change input caps to MIT, the two input resistors, 2w resistors for the amp transistors, and wiring.
This was also completed without any problems and also improved the sound a tad more.

The last mod attempted was to change all the cheap resistors to wire wound Mills for the high watts, and PRP's for the others.
Every resistor was checked with a meter for correct value and against the schematics before they were swapped out.
Am 99.99% sure that the resistor values are correct.

In any case, this last mod; changing the resistors is where I ran into problems.
The fueses on the amp boards immediately blow when the power switch is turned on.
There are no fried circuits or shorts I can see due to solder leaks or leads, etc.
This happens whether I connect one or both of the amp boards.

I checked the power supply circuit and the input and output voltages are correct, so do not suspect the problem is in the power supply circuit.

As a last resort, I tried replacing the old resistors into one of the amp boards, but still have a problem with blowing the fuses.

Can anyone offer some advice as to any tests I can do.
I do not have a scope, but can obtain one if necessary.

Also if there is anyone in the USA that can offer to fix this amp for me, that would be entertained as well.
There are no repair shops where I live that will work on this kind of hifi equipment.
Maybe just the amp boards could be shipped out for repairs.

The other option would be to replace the amp boards with one of the many DIY kits available.
Any suggestions on which amp board kit that would work with this power supply circuit would also be considered.

Look forward to any replies.

Cheers.
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Old 7th April 2009, 05:55 PM   #2
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Default IT IS OBVIOUS TO ME

that you either made a fatal resistor mistake or some soldering mistake ....

the way you describe things it seems that it cannot be anuy other option ....

the problem is that if you replaced a resistor in the wrong value there is a grate possibility that you deep fryied some active component of the amp

having the same trouble for both amps means that you made the same mistake for both amps .....

you need to check for mistakes in the resistors .... ( your comment say thatb you are 99.9% sure but how this comes ???? from readings on the resistors ??? ohm meter???? or schematic ???)

then you need to check for faulty semis

and then you need to post a schematic

of course you will need tools and knowledge to proceed and it seems to me that this will be the not easy part to do ....

posting a schematic though might help since except me you might get help from others ....

do you really live in japan???? you lucky sob he he he
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Old 7th April 2009, 06:54 PM   #3
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Carefully inspect the solder side of the board under a good quality magnifying glass for solder bridges. The pads tend to be very close and it is very easy to be a bit careless. If you don't find any bridges check each and ever resistor against the schematic to make certain that you didn't swap resistors by accident. I've seen this many times, people swear that they didn't make a mistake but when you brow beat them into rechecking they find their mistake. Take the time and check all the resistors since the amp worked before the resistor swap it makes sense the the problem would be there. Some thing else is always possible.
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Old 7th April 2009, 08:14 PM   #4
hafp is offline hafp  United States
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Thanks for the replies sakis and Andy.
I was very careful at doing the mods, and am pretty sure that there are no solder bridges or mixed up resistors; but like you said, there could always be that possibility...

Any recommendations for these options:

The other option would be to replace the amp boards with one of the many DIY kits available.
Any suggestions on which amp board kit that would work with this power supply circuit would also be considered.
The amp uses a single 1000va 80v toroidal transformer with the filter caps wired in series and feeding the two amplifier board circuits.
The +/- VDC outputs from the power supply filter caps to the amp boards is 45V.

The A-250 output is rated at 250wpc, so any amp board kit with the around the same output would be considered.


Also if there is anyone in the USA that can offer to fix this amp for me, that would be entertained as well.
There are no repair shops where I live that will work on this kind of hifi equipment.
Maybe just the amp boards could be shipped out for repairs.

Cheers.
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Old 7th April 2009, 09:08 PM   #5
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I found a good way of finding problems was to remove the output transistors and feed the output of the VAS back into the LTP.
This way you can read volts without blowing fuses.

Of course you could go back to basics and check each component in the amp. Dont just check transistors for shorts but also check the gain of them on a multimeter.
I had a strange fault once when a transistor had a gain of 1 instead of 45.
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Old 8th April 2009, 07:25 AM   #6
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Default dont be so ready ....

Quote:
Originally posted by hafp
Thanks for the replies sakis and Andy.
I was very careful at doing the mods, and am pretty sure that there are no solder bridges or mixed up resistors; but like you said, there could always be that possibility...

Any recommendations for these options:

The other option would be to replace the amp boards with one of the many DIY kits available.
Any suggestions on which amp board kit that would work with this power supply circuit would also be considered.
The amp uses a single 1000va 80v toroidal transformer with the filter caps wired in series and feeding the two amplifier board circuits.
The +/- VDC outputs from the power supply filter caps to the amp boards is 45V.

The A-250 output is rated at 250wpc, so any amp board kit with the around the same output would be considered.

Also if there is anyone in the USA that can offer to fix this amp for me, that would be entertained as well.
There are no repair shops where I live that will work on this kind of hifi equipment.
Maybe just the amp boards could be shipped out for repairs.

Cheers.
to trush the boards ...... give them some time and basicly give them a lot of time .....it can be a mistake so obvious that you dont even see it


often we make unbelivable mistalkes like exchanging P&N transistors or even place rails upside down ....the mistake is there its obvious and you dont even see it ....

post a schematic .... post pictures of your work
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 7th January 2010, 02:18 PM   #7
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hafp,

I know this is an old thread but I was curious as to whether you were able to fix this amplifier. I have been researching Acurus mods and I stumbled onto this thread. If you fixed it, what did you find?
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Old 12th February 2011, 05:51 AM   #8
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For all you guys that insist on working around the problems with this amp, instead of addresing the real problems.
The flat sound of this amp, has to do with #1 poor power supply caps, and #2 a incorrectly designed input circuit.
If you don't address these, the amp will never sound the way it should sound.
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Old 6th May 2011, 02:36 AM   #9
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Hey I was reading a message you wrote about about acurus amps, you suggested the 2 main problems with the amp are the #1 poor power supply caps, and 2 an incorrectly designed input circuit. I got A A100, and i don't know anything about mods to amps. But what are your suggestions to do to make this amp better ? The power supply caps Are those the Elna 10,000uf Lp5's, I have two 22,000uf Elna For Audio caps, the lp5s are 80v and the 22Kuf are 63v and i think the rail voltage is 60v would these work ? I'm stupid if you got any time tell me your thoughts about what to do It would be greatly appreciated. Thanks, Sorry to bother you.
JON
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Old 13th November 2013, 06:47 PM   #10
HankF is offline HankF  United States
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automaticmojo, I've got an Acurus 200x3. Do your criticisms also apply to it? If so, please offer us mods to fix the "incorrectly designed input circuit". Replacing PS caps is easy if the stock ones are low quality.
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