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Old 30th March 2015, 05:55 PM   #1
el156 is offline el156  Portugal
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Default 2SB755/2SD845

Hi !
Does someone knows if i can replace this 2SB755/2SD845 for the 2SA1302/2SC3281 ?
Thanks
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Old 31st March 2015, 01:33 PM   #2
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yes and no it depends if the amplifier features bias adjustments and or if the drivers are fully capable of driving the outputs ( in most cases both is possible )

You may as well go for 2922-1216 and this will save you the metal work ...

State model and brand and i will let you know if its done before successfully..

Kind regards
Sakis
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 31st March 2015, 05:57 PM   #3
el156 is offline el156  Portugal
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Quote:
Originally Posted by east electronics View Post
yes and no it depends if the amplifier features bias adjustments and or if the drivers are fully capable of driving the outputs ( in most cases both is possible )

You may as well go for 2922-1216 and this will save you the metal work ...

State model and brand and i will let you know if its done before successfully..

Kind regards
Sakis
Thank you very much for your reply ! The reason i asked this, is because i have a ONKYO A-45 ,wich has an intermitent problem in one of the channels,sometimes the protection circuit turns on because it detects about -40 Volts in the output of that channel, and i could not find where that voltage comes from because the amp is all DC coupled, so i thought in replacing first the output transistors,and because i dont have and cannot get the 2SB755/2SD845, but have plenty of original toshibas 2SA1301/2SC3281, i thought in replacing for this ones.
Thank you friend
Silvino
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Old 31st March 2015, 06:03 PM   #4
wg_ski is offline wg_ski  United States
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I'll bet it's not the output transistors that's causing that. When output transistors die the result is usually more catastrophic, and not intermittent.
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Old 31st March 2015, 06:03 PM   #5
el156 is offline el156  Portugal
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Here is the scematic of the A-45
Attached Files
File Type: pdf Onkyo-A45 amp.pdf (839.0 KB, 22 views)
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Old 31st March 2015, 06:15 PM   #6
el156 is offline el156  Portugal
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Quote:
Originally Posted by wg_ski View Post
I'll bet it's not the output transistors that's causing that. When output transistors die the result is usually more catastrophic, and not intermittent.
Well, it is not a cold joint, because i rebuilt ALL them in that channel, maybe the best i can do is replacing the transistors one by one from one channel to the other and see what happens...but the problem is that the amplifier sometimes works fine for one or two weeks or even more...hummmm not a easy task i have here...
Thank you
Silvino
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Old 31st March 2015, 06:20 PM   #7
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WG_ski is right this is not coming from the output stage give me a few minutes to look at it and i will let you know

Keep the 1302-3281 it is impossible to find original make nice P3A with them ..Trust me it will be very rewarding

Regards
Sakis
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Old 31st March 2015, 06:36 PM   #8
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Truly this will be hard to trace since the amp has a few weak points ( I am referring to similar transistor fails in other similar amplifiers )

you need to check:
--If at the time of failure secondary regulated power supply works properly area of Q902 -901
--Transistor ( dual ) A995 has a report of failure in many models
--Q302-303and 301 might also be in some failure mode
--IC 4558 works as a servo amplifier you might wana replace this as a precaution also capacitors related to it

A heat gun is your friend Use a nose that can spot heat to a small area put it close to any of those transistors for a small period of time it might show you where the fault is .Hot air soldering station will work far better there .

Freeze spray might also help working exactly the other way around

To learn something .... Transistor except on off types of failure where the most common is shorted between C and E
In small transistors until drivers size there is also mechanical failure that means that the die inside from temperature"fatigue" ( going hot and cold all the time ) looses contact with the pin ...Force it to warm up or cool down and will normally restore or present operation or failure respectively ...

the 0.0001%....exception: I repair 1000 audio devices per year .... Only once i had an output transistor presenting the same "mechanical " error IE contact only if warmed up so if you run out of option apply diagnostics there also .

Kind regards
Sakis
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

Last edited by east electronics; 31st March 2015 at 06:41 PM.
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Old 31st March 2015, 06:39 PM   #9
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Avoid swapping parts ..statistically will create more trouble than solving them ...Its a bad practice and it should be used only as a last resort .
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 31st March 2015, 06:56 PM   #10
el156 is offline el156  Portugal
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Thank you for your time and interest !
I already used two freezing spray cans in this amplifier and heated localy in all the bad channel with no results (i have a Hakko hot air), so this problem is not sensitive to cold or heat...so i will replace the more components i can and see what happens.
And about the 2SA1302/2SC3281 ,it is still possible to buy the original Toshiba ones, but ASWO from Germany asks about 45 Euros for one as a Pioneer P/N.
Thank you
Silvino
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