Electronics

Livio · Guest

Hello my friends!
I have a little problem with this amp and I'm wondering if anyone has
had similar situation.
I got this amp with both channels burnt out, so I changed all output
transistors, their drivers and their respective resistors. Also some
other transistors were shorted or just leaking and of course, both IC's
PA0016 were out too. After I changed all of this, everything seemed to
be ok. Without signal applied to input or with signal and volume pot
turned up to 1/4 of total turn, it was ok. Output transistors and
drivers becomes warm after very short time but temperature doesn't
change or goes up. Quiescence current was about 200 mA. I don't know if
it's ok because I don't have complete service manual, just schematic
diagram.
I noticed that output voltage is on one channel 2-4 mV but on the other
it was constantly varying from 8-40 mV. Voltages on PA0016 were also as
stated in schematic and stable. This second channel literally has burn
out after I turned volume a bit higher than 1/4.
Because those IC's PA0016 are pretty expensive, I checked once again the
channel that remained alive, found nothing wrong and I've left it to
play some more time to see what will happened. And it happened again.
Just this time it was a bit later and at higher power (about 1/2).

Could it be because I didn't put inside exact original transistors but
direct replacements ( for drivers and some transistors around PA0016,
all of them in signal path or in power supply circuitry)?
Does anybody know how is quiescence current adjusted on this amp? I
guess PA0016 is in charge for this.

SO, it's a bit long one, but I'd like to fix this amp because I already
invested some money in it and it looks pretty mighty. I hope it will
sound up to its looks. :-)

Thanks in advance.

Best Regards,
Livio

Mark D. Zacharias · Guest

Sounds exactly like counterfeit output transistors. It's happened to me as
well, also on a Pioneer using the PA0016's. If you're in the US buy the
outputs or subs from B & D Enterprises (Bdent.com) or direct from Pioneer.
Original 2SA1302 and 2SC3281 transistors were discontinued by Toshiba long
ago, so any new ones you find are definitely fakes.

Mark Z.

daddamarco · Joined: 12 Aug 2006 Posts: 2

Hello, I'm marco and I'm in a your similar situation.
I have an amp AX-450 of Pionner and i have both the channel born, too.
I change the output transistor (2SC3181, 2SA1264) but the amp don't work correctly the sound was very small and distorted...
i'm looking for the PA0016 datasheet, i think is it because now i can heard nothing, But i can't find it... Do you know where i can find it? i've search anywhere but i couldn't found it...! Sad

I'm disperated Crying or Very sad

And do you know where can i buy it? which i find, they are very expensive and they come all from the china...

Can you help me, please?
Smile

Thank you...
Marco[/quote]

neon · Joined: 25 Feb 2006 Posts: 570

one test you should do before you try to play it. is shots the inputs and short it to ground. the output and all the parts should be colds there is no work being done. leave like that for a while [temperatures changes slowly] I Suspect that after changing these parts to probably better your amplifiers goes into oscillation and unless you have a scope you can't tell. A meter analog or digital is too slow to tell you anything but the rise in temperature on the output can give you an indication of what goes on. Only quetient current should flow with no input if you measure 200ma with shorted input that is your solution OSCILLATION.

daddamarco · Joined: 12 Aug 2006 Posts: 2

I think the problem isn't oscillation, because the output transistors are cold, i think there isn't a correct input. i have tried to change the transistor which drive the ouput, but the thing got worse, now there isn't output. I think i have burned other stages during the changes of the transistor.
the PA0016 i don't know what are, i think they are the cause, but if i can't change them or know if are burned i can't move...

I have also tried to search in the B & D Enterprises (Bdent.com) but i haven't find anything...

I'm very disperated... Crying or Very sad

Hoping in your help, i want thank you

neon · Joined: 25 Feb 2006 Posts: 570

then if you are shure that there is no oscillation trouble the look at the power supply as a source of trouble. The output capacitor if there is one in series with the output can be leaking or bad and that can cause this kind of problems. datasheetlocator.com you can find most parts specs. Finaly there are no counterfeit parts why produce discontinue parts when we all know that parts can be replaced by similar specs or better. China buy parts from the same supplier as you and me. discontinue parts means there are better parts available for replacement or the packging is non convential for design.Next time do not apply any signal just let it stay there for a while there should be no heating of any sort. you jump the gun and see if it blow up and it will.

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