Transistor Help?????

jocko_nc · 26th October 2006, 08:25 PM

I posted this at another site as well. This is my first attempt with output transistors...

--------------------------------------------------------------------------------

Please indulge my rank amateur status with this... I really want to tackle this myself, if possible.

I have a CA 400 integrated amp that I have never seen work. It was obviously not the main fuse. Further inspection, I found a symptom of the problem, an internal fuse blows as soon as power switch is completed. It is one of two 2.0 A fuses that seem to run between the secondary of the transformer and the output transistors. There are four transistors in matched pairs, each pair connected to a 2.0 A fuse. It looks like R and L channels to me, with one set shorted out. Is that an expected outcome for a blown transistor? Am I correct that these 2.0 A fuses protect the main outputs? The input fuse is only 2.5 A.

I have the unit largely apart right now such that I can get to the transistors, even with my meathooks. Should I pull the transistors (the ones that I trace to the fuse in question) and test? Is this a logical fix?

Just wanted some advice before I really dig in. This is a really pretty unit. Beautiful.

Thanks in advance.

A671 4M 2 and C1061 4M 5 are the transistors. They have what looks like an Hitachi logo on them.

jocko

I searched ON Semiconductors for suitable replacements. It looks like these are "TO220-style bipolar transistors", 25 watt range. I pulled that from the audio output section. Is it that easy? That is what the OEMs look like. I need to determine whether PNP or NPN construction, how do I do that? Are these suitable for replacement? What am I missing?

I found a paper on how to test.

I am confused and running in circles. Any help would be greatly appreciated.

Thanks,

jocko

Netlist · 26th October 2006, 08:35 PM

Jocko,

Welcome to the forum.

Likely you have broken output transistors.
A671 is in fact 2SA671, PNP
C1061 is 2SC1061, NPN.
If you found how to test them, take them out and measure them as a first step.
Make sure you discharge the main capacitors first before working on the amplifier.
No need to tell you to pull the mains as well.

/Hugo

jocko_nc · 27th October 2006, 04:35 PM

Thanks! I'll get some on their way.

jocko_nc · 27th October 2006, 07:43 PM

I'm getting closer, but still a little dense on purchasing these...

I understand ON Semi is a good source. I found them retail at Digikey.com. I see several part numbers that may work:

As far as volt / amp rating, should I choose a 120V component? They have from 80V to 350V. Why the difference, surely the line voltage isn't stepped up????

Assuming 120V, the part numbers would be MJE15028 and MJE15029. The "G" denoted only lead-free. Would these work for me?

Sincerest thanks for your time and patience.

jocko

Netlist · 27th October 2006, 08:23 PM

MJE15028/29 are reliable components, I'd give it a try.
They are build to withstand a higher voltage than the transistors that are currently in your amplifier so this can't be a problem.
Don't forget to measure other transistors and resistors as well to prevent the new ones from getting toasted again.

/Hugo

26th October 2006, 08:25 PM	#1
jocko_nc diyAudio Member Join Date: Jul 2006	Transistor Help????? I posted this at another site as well. This is my first attempt with output transistors... -------------------------------------------------------------------------------- Please indulge my rank amateur status with this... I really want to tackle this myself, if possible. I have a CA 400 integrated amp that I have never seen work. It was obviously not the main fuse. Further inspection, I found a symptom of the problem, an internal fuse blows as soon as power switch is completed. It is one of two 2.0 A fuses that seem to run between the secondary of the transformer and the output transistors. There are four transistors in matched pairs, each pair connected to a 2.0 A fuse. It looks like R and L channels to me, with one set shorted out. Is that an expected outcome for a blown transistor? Am I correct that these 2.0 A fuses protect the main outputs? The input fuse is only 2.5 A. I have the unit largely apart right now such that I can get to the transistors, even with my meathooks. Should I pull the transistors (the ones that I trace to the fuse in question) and test? Is this a logical fix? Just wanted some advice before I really dig in. This is a really pretty unit. Beautiful. Thanks in advance. A671 4M 2 and C1061 4M 5 are the transistors. They have what looks like an Hitachi logo on them. jocko I searched ON Semiconductors for suitable replacements. It looks like these are "TO220-style bipolar transistors", 25 watt range. I pulled that from the audio output section. Is it that easy? That is what the OEMs look like. I need to determine whether PNP or NPN construction, how do I do that? Are these suitable for replacement? What am I missing? I found a paper on how to test. I am confused and running in circles. Any help would be greatly appreciated. Thanks, jocko

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26th October 2006, 08:35 PM	#2
Netlist diyAudio Moderator Join Date: Jan 2003	Jocko, Welcome to the forum. Likely you have broken output transistors. A671 is in fact 2SA671, PNP C1061 is 2SC1061, NPN. If you found how to test them, take them out and measure them as a first step. Make sure you discharge the main capacitors first before working on the amplifier. No need to tell you to pull the mains as well. /Hugo

27th October 2006, 04:35 PM	#3
jocko_nc diyAudio Member Join Date: Jul 2006	Thanks! I'll get some on their way.

27th October 2006, 07:43 PM	#4
jocko_nc diyAudio Member Join Date: Jul 2006	I'm getting closer, but still a little dense on purchasing these... I understand ON Semi is a good source. I found them retail at Digikey.com. I see several part numbers that may work: As far as volt / amp rating, should I choose a 120V component? They have from 80V to 350V. Why the difference, surely the line voltage isn't stepped up???? Assuming 120V, the part numbers would be MJE15028 and MJE15029. The "G" denoted only lead-free. Would these work for me? Sincerest thanks for your time and patience. jocko

27th October 2006, 08:23 PM	#5
Netlist diyAudio Moderator Join Date: Jan 2003	MJE15028/29 are reliable components, I'd give it a try. They are build to withstand a higher voltage than the transistors that are currently in your amplifier so this can't be a problem. Don't forget to measure other transistors and resistors as well to prevent the new ones from getting toasted again. /Hugo

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