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
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
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
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
Keep the 1302-3281 it is impossible to find original make nice P3A with them ..Trust me it will be very rewarding
Regards
Sakis
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
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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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 .
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
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
I got 110 pairs left ,original, precision matched from Toshiba . I am not willing to give away not even one . All are going to be consumed for personal amusement only !!!
Did you heat outputs also ? Lets think a bit more ....If this was a preamp issue servo should see it and kill it , so what ever happens might be beyond input stage , did you heat drivers also ? It has been some Pioneer failing like that from the drivers ... Then after that you are looking for a ghost ...It will consume time to find.
One more thing when at failure mode voltage in the output is pos or neg ?
Then another thing to study will be grounding ...See how it works make sure that all grounds are correct and firm
One more thing when at failure mode voltage in the output is pos or neg ?
Then another thing to study will be grounding ...See how it works make sure that all grounds are correct and firm
You got them in the Good old Days !!! By ASWO sells them, you have almost 5000 Euros worth in that Toshibas !!!
Silvino
Sorry for my ignorance, but i have been away for Solid State for a long time,and have been working with tubes this last years...can you explain what is that P3A ? or give me a link ?
Thank you
Silvino
Yes, i did heat the outputs ,the drivers, and ALL the other transistors, and freeze them as well, so this is NOT a heat or cold sensitive problem, and i think the best way is to replace the more parts i can in that channel and see what happens, and it will consume lots of time, and next time it happens i will try to measure all the voltages in that channel, i hope it helps...well it is not an easy task ,i know...AH when it fails, i have a negative voltage in the output.
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Next time it happens - first make sure the DC bias servo isn't Doing Something Stupid (to disable, temporarily remove R346). And then try to figure out why Q306 is losing drive. For it to slam the minus rail without releasing magic smoke, and no issues with the bias servo this must be happening. Start with voltage across R329 and work backwards through the input stage.
here is some interesting reading about the P3a
http://www.diyaudio.com/forums/solid-state/164756-p3a-comparison-table-long.html
I trust that when you look at the schematic you will not be surprised Remember that P3A is a CFP so not easy to understand for everyone
Given the simplicity of the circuit and cost of original boards you will be 10.000 times more surprised when you listen to it ....It will change your aspects about tube sound for ever ....
http://www.diyaudio.com/forums/solid-state/164756-p3a-comparison-table-long.html
I trust that when you look at the schematic you will not be surprised Remember that P3A is a CFP so not easy to understand for everyone
Given the simplicity of the circuit and cost of original boards you will be 10.000 times more surprised when you listen to it ....It will change your aspects about tube sound for ever ....
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