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Old 24th November 2005, 06:34 PM   #1
namcir is offline namcir  Philippines
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Default help blown yamaha amp

hi to all
i have been around a lot but this is my first post.
i just blown my yamaha amp buy adjusting its bias almost to the max. fortunately nothing in the output devices failed ( i think so) but the power supply devices blew up (swithch mode) leaving black smoke on its surroundings. do anybody have the same expereince? what did i do wrong? help
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Old 24th November 2005, 06:42 PM   #2
MikeB is offline MikeB  Germany
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Possibly you overheated your outputdevices, bias to max might have been several amperes. Solder out one of the outputdevices and measure it. They are very likely to be shorted. In this case i would consider this amp a complete loss...

sorry,
Mike
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Old 25th November 2005, 07:43 PM   #3
namcir is offline namcir  Philippines
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thanks Mikeb for your reply:
yes it is a big loss for me maybe i would be careful next time i tinker to my equipment. now i need a service manual to be able to service it properly could anybody help me acquire one? the model is yamaha pro-audio P7000s. please help
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Old 25th November 2005, 08:38 PM   #4
nikwal is offline nikwal  Sweden
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My experiences with switch mode psu's says that if one component there fails MANY others probably will..
I've looked at a couple of yamaha schematics on pdf and they are'nt too complicated in the power amp , You could at least try to measure the transistors with mutimeter diode function, dont rely on it though! transistors may be "half" broken..
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Old 25th November 2005, 09:05 PM   #5
anatech is offline anatech  Canada
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Hi RICMAN,
Yamaha normally has good protection networks and may be in shutdown mode. With any luck, you just killed the outputs, maybe drivers and more.

In general, leave bias settings at factory default. This is more true with pro amps that have to be reliable.

-Chris
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Old 25th November 2005, 09:08 PM   #6
anatech is offline anatech  Canada
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Hi RICMAN,
Rereading, I see you have let the really expensive smoke out of the box. Could be fun, but not impossible to fix.

To repair switching supplies, you need a way to vari the power so it doesn't just go bang if there is another fault. Another bipolar variable power supply may allow you to troubleshoot and fix the output stage.

Wishing you luck with this.

-Chris
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Old 26th November 2005, 02:11 PM   #7
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Default The work to do, i am afraid, is more ressurection than repair

Because of switching power supply and over bias....extremelly overbiased...will be lucky to find fusistors burned.

I think this amplifier soul is already in the skies.

Sorry....bad luck for you....a hard to work to fix...and no guaranteed that the cost of parts are adequated to the equipment used market value....maybe parts turn expensive to put it in order again....those output transistors are highly selected...they are very well matched...hard to find matched units to substitute them....factory use to order sequence of transistors from the same silicon wafle...almost identical units.

regards,

Carlos
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Old 26th November 2005, 02:21 PM   #8
adason is offline adason  United States
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hi ricman

i once had similar problem with an old akai power amp
it had switching supply to make it light and sleak, which died after a while
i replaced it with outside trafo/rectifiers and caps
sounds great till now

i would not waste time with switching power supply
get the external and start replacing blown parts in the amp
don't give up

good luck
e
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Old 26th November 2005, 05:25 PM   #9
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Default Good idea...removing switching supply and installing a standard supply

Will be more easy to fix...as two problems at same time is complicated...to fix the amplifier you need to trust in your supply.

That's a very good idea.....remove supply, substitute by another you prepare, needing more voltages will be easy to prepare with zener and transistors...just tell me the voltage you have and the voltages you need and i can do it for you...and them go to fix the amplifier.

Have some schematic?.....without it may be more difficult...but not impossible.... remove transistors, one by one, in the power unit, and check them...in advance...disconnect all supply wiring...cut keeping color code into the amplifier board...and measure from plus to ground and from negative to ground searching for short circuits....but remove supply.... as the short can be produce be the supply....well...working hard...you may ressurect it.

regards,

Carlos
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Old 26th November 2005, 08:38 PM   #10
adason is offline adason  United States
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here is the pic of that akai amp
it was part of very fancy mini hifi
amp was the best part of it
preamp sucked, tuner and deck was quite good

it has two huge hybrid power packs inside and with new power supply outside (capacitors are inside the amp) can deliver clean 75 watts
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