Hi all,
I'm new to the DIY forums,
I have a Nakamichi PA-1004 amplifier that has recently began emitting some really terrible sounds during playback.
I tore it down to check things out and discovered a burned resistor in the circuit with what I believe are driver transistors.
There are two A1023 Transistors near each other, and in the middle of them is a resistor (the burned one) that is connected across the pins 1 and 3 (Emitter and Base respectively) of one of the A1023's. Sadly it is burned too badly to identify its original color bands.
I am more than happy to take photos or even draw up a partial diagram of the circuit I'm talking about if need be.
I have an above average understanding of electronics, though not proficient at it, and I do have many tools at my disposal for testing including a higher end DMM made by Amprobe, and two Oscilloscopes (one is an old 2 channel and the other is a newer 300MHz 4 channel)
I'm relatively new to repairing amps, but I'm eager to learn more... I already checked the A1023 transistors and none of the legs appear to be shorted to one another, and the readings are almost identical, so I'm fairly confident they're still OK.
Any help is appreciated. If you need pics or a drawing please let me know.
Thanks,
Aaron
I'm new to the DIY forums,
I have a Nakamichi PA-1004 amplifier that has recently began emitting some really terrible sounds during playback.
I tore it down to check things out and discovered a burned resistor in the circuit with what I believe are driver transistors.
There are two A1023 Transistors near each other, and in the middle of them is a resistor (the burned one) that is connected across the pins 1 and 3 (Emitter and Base respectively) of one of the A1023's. Sadly it is burned too badly to identify its original color bands.
I am more than happy to take photos or even draw up a partial diagram of the circuit I'm talking about if need be.
I have an above average understanding of electronics, though not proficient at it, and I do have many tools at my disposal for testing including a higher end DMM made by Amprobe, and two Oscilloscopes (one is an old 2 channel and the other is a newer 300MHz 4 channel)
I'm relatively new to repairing amps, but I'm eager to learn more... I already checked the A1023 transistors and none of the legs appear to be shorted to one another, and the readings are almost identical, so I'm fairly confident they're still OK.
Any help is appreciated. If you need pics or a drawing please let me know.
Thanks,
Aaron
Hi, are both channels burned? if one channel is good you should be able to get the value from that. if not then sourcing a schematic would be the next step.
Tony.
Tony.
Hi Tony,
Thanks for the response!
I feel a bit embarrassed now, I wasn't thinking very clearly at first because I was upset that my amp was not working correctly and basically running through disaster scenarios in my head...
Anyway, after I posted on here, I went back and looked at everything again, and hand drew out the circuit for the portion that needs repaired, and it hit me that only one is burnt.
After a closer inspection the resistor that's in the same position electrically on the other "side" of this circuit is a 22ohm.
What's odd though about this section is the A1023 is typically used as a driver transistor if I'm not mistaken, and there's only two of them in this location on my 4 channel amp... Maybe I'm not dealing with a section of board using these transistors as drivers for output channels?
Thanks,
Aaron
Thanks for the response!
I feel a bit embarrassed now, I wasn't thinking very clearly at first because I was upset that my amp was not working correctly and basically running through disaster scenarios in my head...
Anyway, after I posted on here, I went back and looked at everything again, and hand drew out the circuit for the portion that needs repaired, and it hit me that only one is burnt.
After a closer inspection the resistor that's in the same position electrically on the other "side" of this circuit is a 22ohm.
What's odd though about this section is the A1023 is typically used as a driver transistor if I'm not mistaken, and there's only two of them in this location on my 4 channel amp... Maybe I'm not dealing with a section of board using these transistors as drivers for output channels?
Thanks,
Aaron
I'm not sure what they would be for if there are only two sections with those transistors, but four channels...
The other thing that those transistors might be used for would be VAS I guess, but I'd still expect to see four identical sections for four channels.
It could be time to get googling (or contact Nakamichi) for a schematic (note that if you do find one unless it is on nakamichi's site you should not post it or a link to it here). It would be nice to know what the likely cause of the resistor smoking is. Replacing just the resistor might work but it seems likely that something else has failed causing excessive dissipation in that resistor.
Tony.
The other thing that those transistors might be used for would be VAS I guess, but I'd still expect to see four identical sections for four channels.
It could be time to get googling (or contact Nakamichi) for a schematic (note that if you do find one unless it is on nakamichi's site you should not post it or a link to it here). It would be nice to know what the likely cause of the resistor smoking is. Replacing just the resistor might work but it seems likely that something else has failed causing excessive dissipation in that resistor.
Tony.
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Took a fresh look at this amp today after a nice sleep, and with a clear head, and a phone call to a friend who used to build high end amps for a living, I determined that these are actually the oscillator driver for the pulse transformer in the PWM section of the power supply. Also determined that BOTH 2SA1023 transistors are shot.
I later called a place I found linked in a buried thread on these forums called CIA Engineering, and turns out he's like 25 minutes from my house, we chatted for a good 15 minutes and then I sent him some pictures. Waiting on a response from him to see what he thinks about the state of this unit and if its repairable...
The general consensus so far is that it most likely IS repairable, but we shall see.
I'm going to attempt to get a schematic from Nakamichi, or perhaps the man behind the curtain Steve Mantz of Zed Audio as this model amp is apparently one of his.
Thanks,
Aaron
I later called a place I found linked in a buried thread on these forums called CIA Engineering, and turns out he's like 25 minutes from my house, we chatted for a good 15 minutes and then I sent him some pictures. Waiting on a response from him to see what he thinks about the state of this unit and if its repairable...
The general consensus so far is that it most likely IS repairable, but we shall see.
I'm going to attempt to get a schematic from Nakamichi, or perhaps the man behind the curtain Steve Mantz of Zed Audio as this model amp is apparently one of his.
Thanks,
Aaron
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