As noted a FEW times before; it is FOUR hundred watts of power dissipation capability; am not intending to use just one 100w to test 100w+ amps.
Also noted a few times it is mounted to an aluminum heat sink harvested from an amp; is well suited.
Perhaps I should have posted an image of it instead of using words to describe it......
For the power + / - someone commented about missing polarity labels. I had them labeled just "Power" originally since that is what they are (i.e. a/c and in this cause sine waves within 20hz-20khz). But yielded and added the polarity labels since I was the one asking for help.
Noted for the 75% safety test limit.
Oh dear, that is more inline with what I experienced and was first thinking. But as you see in this thread people agreed the slight difference connection of the circuit to the speaker terminals do not make a difference. (there is of course nuance, and those that said the circuits are equivalent did mention the specific "law")
But your comments about the circuit are only speaking about 3 resistors....with no mention of the fourth resistor in the circuit.
Can you please address that missing bit?
The second and third images within the first post are the same circuit, just connected to the amplifier differently.
And thank you so much for the reply. Of course am familiar with ohms law and the few formulas of. It was needed for creating the circuit.
Funny note, before ordering the resistors, I did not know of the Ohms law; mroe specifically the r/i/v/ohms "Mechanics". I was looking to have 300w / 8ohms and four banks....thinking I would just need to wire 3 resistors in parallel for 300w / 8ohm...
Was surprise when wired up like that and measured MUCH less resistance....then I learned about what resistance actual is....a probability of an electron passing or not. that would be independent of other resistors in the circuit. I now think of them more like a brake (more fundamentally a "friction" of a specific amount)
I revisited this post to updated on the Amp repair part.
Was surprised when I checked for what blew that I only found the power transistor pair shorted, both three way short and one side of the emitter resistor opened / spoiled.
I did check a few other components in the amp section and saw no other spoiled components.
que lack of experience; So concluded the diagnoses with just those components needing replacement.
Didn't check the pre-amp (driver section?) lol and is an error I see now. VERY likely there would be issue in there.
So....by happenstance there was a TX-NR708 for sale with spoiled DSP chip for 30$CAD (my avr is a tx-nr709) Four years diff between amp release dates but share same amp section.
I took the easy route for now, just dropping in the TX-NR708 amp into the 709. All good there.
Am still going to go through the exercise of repairing the original amp I blew.
I found a spoiled resistor when checking out the pre-amp (Driver?) section left channel (the one that blew), that was connected to one of a npn/pnp pair. both those transistors passed the diode test.
Should those be tested out of circuit for more comparative, or is diode test good enough to trust their okay? I have a cheap transistor tester that gives additional measures.
All that said, is all I found so far, and there isn't much left to check. Note am not sampling, am checking each component in the path up to power transistors....and now I'll be checking after just incase there is a short after the power transistors...actuall haven't checked that lol
So I wonder if the sequence was the resistor "failed" (not open, just really high resistance compared to what it should be) and it caused the driver transistor (I think that's what it is) to not do right, and that cause the power transistors and emitter resistor to fail.
I see experienced people talk about driver transistors and driver board ect....is that same as what I would call "Pre-amp"?
Was surprised when I checked for what blew that I only found the power transistor pair shorted, both three way short and one side of the emitter resistor opened / spoiled.
I did check a few other components in the amp section and saw no other spoiled components.
que lack of experience; So concluded the diagnoses with just those components needing replacement.
Didn't check the pre-amp (driver section?) lol and is an error I see now. VERY likely there would be issue in there.
So....by happenstance there was a TX-NR708 for sale with spoiled DSP chip for 30$CAD (my avr is a tx-nr709) Four years diff between amp release dates but share same amp section.
I took the easy route for now, just dropping in the TX-NR708 amp into the 709. All good there.
Am still going to go through the exercise of repairing the original amp I blew.
I found a spoiled resistor when checking out the pre-amp (Driver?) section left channel (the one that blew), that was connected to one of a npn/pnp pair. both those transistors passed the diode test.
Should those be tested out of circuit for more comparative, or is diode test good enough to trust their okay? I have a cheap transistor tester that gives additional measures.
All that said, is all I found so far, and there isn't much left to check. Note am not sampling, am checking each component in the path up to power transistors....and now I'll be checking after just incase there is a short after the power transistors...actuall haven't checked that lol
So I wonder if the sequence was the resistor "failed" (not open, just really high resistance compared to what it should be) and it caused the driver transistor (I think that's what it is) to not do right, and that cause the power transistors and emitter resistor to fail.
I see experienced people talk about driver transistors and driver board ect....is that same as what I would call "Pre-amp"?
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Running an amplifier like yours at its rated undistorted maximum output for more than a few seconds is likely to cause permanent damage to the amplifier, not the load resistors which are designed to run at 80 degrees C or higher.
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You were able to get it working for 30 dollars, count yourself lucky.
Enjoy the music.
If it is working with the new board, don't mess with it, as an experiment, it is not worth it.
Don't load it with dummy loads or whatever.
If you want to learn how to fix audio systems...there are plenty of posts and a knowledgeable community willing to share their experience and time here on this forum.
In India, Onkyo sells a few units a month, it is sold as a high end brand.
As for the broken amp, sell it as scrap, or use it as a learning project.
Or keep it in reserve as a parts donor.
Enjoy the music.
If it is working with the new board, don't mess with it, as an experiment, it is not worth it.
Don't load it with dummy loads or whatever.
If you want to learn how to fix audio systems...there are plenty of posts and a knowledgeable community willing to share their experience and time here on this forum.
In India, Onkyo sells a few units a month, it is sold as a high end brand.
As for the broken amp, sell it as scrap, or use it as a learning project.
Or keep it in reserve as a parts donor.
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The "experimenting" / excersise of fixing the amp is of course with the donor avr and broken amp. the 709 is fixed / working. (i havent checked amp bias of donor amp)
I agree I was "lucky" / was good opportunity, though I had previously bought replacement transistors and pulled a donor emitter resistor tried that repair for a cost of 30$ total, so total is 60$ to repair + I have 708 for whatever.
After buying new components and trying the repair I searched for a used broken one and got lucky with the 708.
The amp I'll be playing / learning / practicing with is the broken spare. I'll be using the donor 708 to test the amp in; obviously?
Of course if successful I'll swap the original and years newer amp into the 709.
I agree internet good resource; communication is tricky but am learning that too.
I agree I was "lucky" / was good opportunity, though I had previously bought replacement transistors and pulled a donor emitter resistor tried that repair for a cost of 30$ total, so total is 60$ to repair + I have 708 for whatever.
After buying new components and trying the repair I searched for a used broken one and got lucky with the 708.
The amp I'll be playing / learning / practicing with is the broken spare. I'll be using the donor 708 to test the amp in; obviously?
Of course if successful I'll swap the original and years newer amp into the 709.
I agree internet good resource; communication is tricky but am learning that too.
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"So I wonder if the sequence was the resistor "failed" (not open, just really high resistance compared to what it should be) and it caused the driver transistor (I think that's what it is) to not do right, and that cause the power transistors and emitter resistor to fail."
More likely; you accidentally shorted the output, frying the output transistors and causing them to short, which in turn caused the resistor to overheat and fail due to dropping more voltage, hence dissipating more power, than it was designed to, due to aforementioned dead short.
Possibly, the resistor burning out/going high protected the driver and the rest of the circuit. But in this scenario, at least the driver should be treated as suspect, and many techs will replace it as a precaution.
A diode test doesn't necessarily prove that a transistor is "good", although it provides an indication for some common failure modes such as open or short.
I've seen transistors which test okay, but completely misbehave in circuit when subjected to higher voltages or different operating conditions. I've also seen transistors pass a diode test, but don't test okay as a transistor ie. component tester shows 2 diodes.
More likely; you accidentally shorted the output, frying the output transistors and causing them to short, which in turn caused the resistor to overheat and fail due to dropping more voltage, hence dissipating more power, than it was designed to, due to aforementioned dead short.
Possibly, the resistor burning out/going high protected the driver and the rest of the circuit. But in this scenario, at least the driver should be treated as suspect, and many techs will replace it as a precaution.
A diode test doesn't necessarily prove that a transistor is "good", although it provides an indication for some common failure modes such as open or short.
I've seen transistors which test okay, but completely misbehave in circuit when subjected to higher voltages or different operating conditions. I've also seen transistors pass a diode test, but don't test okay as a transistor ie. component tester shows 2 diodes.
Follow up
So I managed to repair the amp with the blown left channel. The remaining spoiled components were a few resistors within the driver transistor area. two were much higher resistance and one much lower.
Was super happy to repair it, is moreless my first electronics repair from diagnosis to fix.
What's more, the donor AVR unit, the TX-NR708 that I bought for 30$ sold for parts due to bad "DTS" chip. Common issue is the DSP chip is the BGA connection breaking and results in HDMI video, but no audio.
BUT, it works fine!! no issues with the 708.
So in sum,
Played with my 709 and blew a channel in the process; spent 30$ for a few parts with no luck in repair, then another 30$ for donor AVR. and
Now I have a working 709 and working 708 lol
In addition, for the resistors that were spoiled. I did not have exact values, so needed to make nearly exact same array as the resistor bank I had made earlier.
Super fun and satisfying!
So I managed to repair the amp with the blown left channel. The remaining spoiled components were a few resistors within the driver transistor area. two were much higher resistance and one much lower.
Was super happy to repair it, is moreless my first electronics repair from diagnosis to fix.
What's more, the donor AVR unit, the TX-NR708 that I bought for 30$ sold for parts due to bad "DTS" chip. Common issue is the DSP chip is the BGA connection breaking and results in HDMI video, but no audio.
BUT, it works fine!! no issues with the 708.
So in sum,
Played with my 709 and blew a channel in the process; spent 30$ for a few parts with no luck in repair, then another 30$ for donor AVR. and
Now I have a working 709 and working 708 lol
In addition, for the resistors that were spoiled. I did not have exact values, so needed to make nearly exact same array as the resistor bank I had made earlier.
Super fun and satisfying!
Great that it all worked out!
Often, resistors in that part of the circuit (ie. Driver/output path) are rated to fail under fault conditions and thereby protect the rest of the circuit. Using an array of resistors to make up the resistance value could compromise this design feature. Just something to consider.
Often, resistors in that part of the circuit (ie. Driver/output path) are rated to fail under fault conditions and thereby protect the rest of the circuit. Using an array of resistors to make up the resistance value could compromise this design feature. Just something to consider.
I agree; it could have all turned out much worse!
I think the biggest gain from the experience / exercise was from the testing of components in the spoiled channel. what an effort that is. What's more I had the HUGE benefit of the other channels to compare values to, so no need to look up / determine proper values.
and thank you for letting me know that resistors in that area are sometimes a "fail safe" of sorts.
There was an 83ohm resistor 1/4w I replaced it with a much more robust (1w I'd guess) 83 ohm resistor. Putting it in I understood the risk that it would not spoil nearly as quickly.
noted about the resistor array's; I hadn't considered the issue for those in this context. though did intend to get proper spec in there. I want to put the original amp back into the 709. It could be as much as four years "newer" and the resistor arrays and 1w resistor look so "janky" in there lol
I think the biggest gain from the experience / exercise was from the testing of components in the spoiled channel. what an effort that is. What's more I had the HUGE benefit of the other channels to compare values to, so no need to look up / determine proper values.
and thank you for letting me know that resistors in that area are sometimes a "fail safe" of sorts.
There was an 83ohm resistor 1/4w I replaced it with a much more robust (1w I'd guess) 83 ohm resistor. Putting it in I understood the risk that it would not spoil nearly as quickly.
noted about the resistor array's; I hadn't considered the issue for those in this context. though did intend to get proper spec in there. I want to put the original amp back into the 709. It could be as much as four years "newer" and the resistor arrays and 1w resistor look so "janky" in there lol