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
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)
These can be hard to find (I couldn't) but I now think I *might* know someone who has a few (2sc2565/2sa1950)
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
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
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
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
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
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
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.
"o/ps 2SD555 and B600" means output devices were 2SD555 and 2SB600.
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
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
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
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
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
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
transistors
Just removed the 2SD555 & 2SB600. No resistance on 2SB600. 1ohm on 2SD555. What do you think ?
Tom
Just removed the 2SD555 & 2SB600. No resistance on 2SB600. 1ohm on 2SD555. What do you think ?
Tom
proceeding w/further testing w/question
After determing the ouput transistors were dead, testing further back exposed 2SD381 and 2SB536 to be suspect. I'm continuing with testing, noting suspects and ordering replacements. QUESTION- Are the drivers the two transistors with the mini heat sinks ? Again, please forgive me for these apparently fundamental queries.
Tom
After determing the ouput transistors were dead, testing further back exposed 2SD381 and 2SB536 to be suspect. I'm continuing with testing, noting suspects and ordering replacements. QUESTION- Are the drivers the two transistors with the mini heat sinks ? Again, please forgive me for these apparently fundamental queries.
Tom
Hi Tom,
Yup, Q707, 708. They are on the larger mini heatsinks. 120V 1.5A 20W hFE~110. Try 2SA1667 / 2SC4381. The older 2SA968 / 2SC2238 would have been my choice ealier in time - NLA.
-Chris
Yup, Q707, 708. They are on the larger mini heatsinks. 120V 1.5A 20W hFE~110. Try 2SA1667 / 2SC4381. The older 2SA968 / 2SC2238 would have been my choice ealier in time - NLA.
-Chris
Updated findings. The following parts failed testing:
Drivers - 2SD381 & 2SB536
TR - 2SA733 & 2SC2088
Diode - VD1212
RES - 5.6kohm 5% 1/4w
Question: Would these be okay to substitute w/NTE cross ?
Tom:
😕
Drivers - 2SD381 & 2SB536
TR - 2SA733 & 2SC2088
Diode - VD1212
RES - 5.6kohm 5% 1/4w
Question: Would these be okay to substitute w/NTE cross ?
Tom:
😕
Hold on here
Hi Tom,
When installing NTE type parts, please do not forget to soak everything in gasoline and light it as you walk away. When you use these replacement parts, you are wasting your time and money. They seem to work okay for TV's for a while. They are useless for audio or anything else pretty much.
Parts with real numbers are not that hard to find. Use them. DO NOT use the NTE manual to find a substitute. Use the above instructions if you intend to do so. Made my point?
2SA1667 and 2SC4381 are better than good. I used to use 2SA968B and 2SC2238B for drivers (NLA) Anything similar and Japanese is good. Try 2SA1015 and 2SC2240 for the other pair. These should be easy to find. The VD1212 is a varistor. If NTE has the same thing, use that. The original is much preferred. The VD1212 loks like a bead on a wire. It may measure open depending on your meter. Normally a low current device, I do not have to change them. Measure the voltage drop across it in both directions connected to a 9V battery through a 9K ~ 10K resistor. It is for temperature compensation. No comment on the resistor.
-Chris
Hi Tom,
When installing NTE type parts, please do not forget to soak everything in gasoline and light it as you walk away. When you use these replacement parts, you are wasting your time and money. They seem to work okay for TV's for a while. They are useless for audio or anything else pretty much.
Parts with real numbers are not that hard to find. Use them. DO NOT use the NTE manual to find a substitute. Use the above instructions if you intend to do so. Made my point?
2SA1667 and 2SC4381 are better than good. I used to use 2SA968B and 2SC2238B for drivers (NLA) Anything similar and Japanese is good. Try 2SA1015 and 2SC2240 for the other pair. These should be easy to find. The VD1212 is a varistor. If NTE has the same thing, use that. The original is much preferred. The VD1212 loks like a bead on a wire. It may measure open depending on your meter. Normally a low current device, I do not have to change them. Measure the voltage drop across it in both directions connected to a 9V battery through a 9K ~ 10K resistor. It is for temperature compensation. No comment on the resistor.
-Chris
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