Nikko Alpha II amp troubleshooting

livetoski · 21st February 2005, 06:58 PM

Hoping someone out there can put me in the right direction. I have a Nikko Alpha II power amp with audio output thru only the left channel. It gives equal voltage at the 5.0 amp fuse holders with the fuses removed. If you replace both fuses and power up, it remains in "protect" mode. Now, if I remove the right channel fuse, power up, audio out of the left channel is established. In this state, with power still on, attempting to replace the right channel fuse causes it to immediately blow. Any ideas short of bring it to a pro ? Thanks

BrianDonegan · 21st February 2005, 07:23 PM

Not definite, but I would bet you have dead output transistors in the right channel. You can test this pretty easily by (with power off) checking the resistance between the pins of the transistors mounted on the heatsink. If they are bad, they will show 0 ohms.

These can be hard to find (I couldn't) but I now think I *might* know someone who has a few (2sc2565/2sa1950)

anatech · 21st February 2005, 07:23 PM

Hi livetoski,
How much experience / test equipment do you have?
While in protect mode, what are the amplifier's DC voltages before the relay?

One thing to consider, a good tech is worth his / her weight in gold. A bad tech is everyones worst nightmare.

-Chris

anatech · 21st February 2005, 08:13 PM

Hi Tom,
The original o/ps were 2SD555 and B600. You can use the new On Semi devices or MJ15024 and MJ15025.

Protection circuit will detect either high DC offset (above a few volts) or excessive current through the emitter resistors. You need to find out which is tripping the protection circuit.

-Chris

livetoski · 21st February 2005, 08:39 PM

What components do I specifically begin testing and what am I looking for ? I'm a little weak on some of the terminolgy here... what is o/ps 2SD555 and B600 referring to?

Tom

BrianDonegan · 22nd February 2005, 12:25 AM

Sorry, I was confusing it with the Alpha 230 when I mentioned the 2sc2565's.

"o/ps 2SD555 and B600" means output devices were 2SD555 and 2SB600.

anatech · 22nd February 2005, 12:54 AM

Hi Tom,
I don't think the output transistors are shorted. Please measure the DC offset from the emitter resistor center and let us know what it is. Is there any way you coud post the schematic for the Alpha II. Mine is gone.
Thanks Tom!

-Chris

livetoski · 22nd February 2005, 06:13 AM

Couple more questions before I proceed here... Having some trouble locating/identifying the emitter resistor. I can scan the schematic and attach tomorrow if that will help. Next, what "state" should I perform the voltage check, that is, with the 5.0 amp fuse in place, which puts the amp in protect mode, or without the fuse, which releases the protect mode, enabling the left channel ? Sorry for all the questions, as this is my first amplifier repair attempt.

Tom

livetoski · 22nd February 2005, 06:13 AM

After submitting the last post, I realized that I obviously need to have the fuse in place to send current to the right channel main amp. Now to locate the emmitter resistor.

Tom

livetoski · 22nd February 2005, 06:04 PM

Here the schematics of the Alpha II main cb and Protector cb. I've included the voltages measured at the noted points.

Tom

21st February 2005, 06:58 PM	#1
livetoski diyAudio Member Join Date: Feb 2005 Location: Northern New England -USA	Nikko Alpha II amp troubleshooting Hoping someone out there can put me in the right direction. I have a Nikko Alpha II power amp with audio output thru only the left channel. It gives equal voltage at the 5.0 amp fuse holders with the fuses removed. If you replace both fuses and power up, it remains in "protect" mode. Now, if I remove the right channel fuse, power up, audio out of the left channel is established. In this state, with power still on, attempting to replace the right channel fuse causes it to immediately blow. Any ideas short of bring it to a pro ? Thanks

21st February 2005, 07:23 PM	#2
BrianDonegan diyAudio Member Join Date: Dec 2004 Location: Rock Ridge	Not definite, but I would bet you have dead output transistors in the right channel. You can test this pretty easily by (with power off) checking the resistance between the pins of the transistors mounted on the heatsink. If they are bad, they will show 0 ohms. These can be hard to find (I couldn't) but I now think I might know someone who has a few (2sc2565/2sa1950) __________________ Twisted Pear Audio

21st February 2005, 08:39 PM	#5
livetoski diyAudio Member Join Date: Feb 2005 Location: Northern New England -USA	getting started... What components do I specifically begin testing and what am I looking for ? I'm a little weak on some of the terminolgy here... what is o/ps 2SD555 and B600 referring to? Tom

22nd February 2005, 12:25 AM	#6
BrianDonegan diyAudio Member Join Date: Dec 2004 Location: Rock Ridge	Sorry, I was confusing it with the Alpha 230 when I mentioned the 2sc2565's. "o/ps 2SD555 and B600" means output devices were 2SD555 and 2SB600. __________________ Twisted Pear Audio

22nd February 2005, 06:13 AM	#8
livetoski diyAudio Member Join Date: Feb 2005 Location: Northern New England -USA	proceeding with testing Couple more questions before I proceed here... Having some trouble locating/identifying the emitter resistor. I can scan the schematic and attach tomorrow if that will help. Next, what "state" should I perform the voltage check, that is, with the 5.0 amp fuse in place, which puts the amp in protect mode, or without the fuse, which releases the protect mode, enabling the left channel ? Sorry for all the questions, as this is my first amplifier repair attempt. Tom


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

21st February 2005, 07:23 PM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi livetoski, How much experience / test equipment do you have? While in protect mode, what are the amplifier's DC voltages before the relay? One thing to consider, a good tech is worth his / her weight in gold. A bad tech is everyones worst nightmare. -Chris

21st February 2005, 08:13 PM	#4
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Tom, The original o/ps were 2SD555 and B600. You can use the new On Semi devices or MJ15024 and MJ15025. Protection circuit will detect either high DC offset (above a few volts) or excessive current through the emitter resistors. You need to find out which is tripping the protection circuit. -Chris

22nd February 2005, 12:54 AM	#7
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Tom, I don't think the output transistors are shorted. Please measure the DC offset from the emitter resistor center and let us know what it is. Is there any way you coud post the schematic for the Alpha II. Mine is gone. Thanks Tom! -Chris

22nd February 2005, 06:13 AM	#9
livetoski diyAudio Member Join Date: Feb 2005 Location: Northern New England -USA	Answered one of my own questions After submitting the last post, I realized that I obviously need to have the fuse in place to send current to the right channel main amp. Now to locate the emmitter resistor. Tom

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Nikko Alpha 220 HELP	tombradvica	Parts	4	7th May 2011 02:24 AM
Nikko Alpha Ii Schematic	sakis	Solid State	6	11th June 2009 10:42 AM
Nikko Alpha 440 and 450	lazyjoe	Solid State	0	3rd September 2008 10:00 PM
Nikko Alpha 220	GEirin	Solid State	4	17th April 2008 08:34 PM
Nikko Alpha 130	ecliptica	Parts	1	29th January 2004 10:16 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read