Hi all,
I'm currently trying to make an amplifier, so for that I used the driver PCB from an Onkyo NR609, and I have build my own PCB for insert the PCB driver :
The PCB driver is inserted in the 9pin connector on my PCB. GND of the PCB driver is grounded via the pin above the 9pin connector.
The Bias transistor is in a hole in the heatsink.
I tested my amp yesterday for 30min with music without problem, the offset on the output was arround 2mV, nothing hot, all fine.. But suddenly the capacitor C5440 (on the original schematic) has exploded :/
I don't understand why... What can be wrong ?
FOR INFORMATION, I have not mounted the componants for the DC protection, so there are only the output stage, driver PCB and output filter mounted on the PCB.
I'm currently trying to make an amplifier, so for that I used the driver PCB from an Onkyo NR609, and I have build my own PCB for insert the PCB driver :
The PCB driver is inserted in the 9pin connector on my PCB. GND of the PCB driver is grounded via the pin above the 9pin connector.
The Bias transistor is in a hole in the heatsink.
I tested my amp yesterday for 30min with music without problem, the offset on the output was arround 2mV, nothing hot, all fine.. But suddenly the capacitor C5440 (on the original schematic) has exploded :/
I don't understand why... What can be wrong ?
FOR INFORMATION, I have not mounted the componants for the DC protection, so there are only the output stage, driver PCB and output filter mounted on the PCB.
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Nope, I just re-used the PCB driver from the Onkyo, so this PCB is "original", not assembled by me. I mounted a 9pin connector on MY PCB, and inserted the PCB driver.
That cap could only explode because of a fault elsewhere causing the voltage across it to rise. Nothing else could do it. If the cap were inserted incorrectly it would just silently fail, there is not enough voltage across it under normal conditions to cause catastrophic failure. If it went leaky or short circuit it would just reduce the bias to the output stage.
Sounds to me like the driver stages have failed catastrophically and/or the the outputs as well.
Sounds to me like the driver stages have failed catastrophically and/or the the outputs as well.
the 10 ohm with the coil in parallel have to be very close to the base of the power transistors, I guess there is a high frequency oscillation in the output stage. That will cause a high current through this cap and heat it up.
Hmm it can be the reason.
But the tracks on my PCB are not really long, and if I compare to the orignal PCB of the AVR, the tracks are similare...
Other point, when the issue appeared, I have pushed the volume for 10s (maybe 40W to the speaker), and lowered the volume. The issue appear at this point.
The cap was very hot.
The only component that I have not mounted on my PCB is capacitors between the Power Ouput and the GND (C6642 and C6652) :
In this case, C6642 is in // with the RC filter on the ouput.
But the tracks on my PCB are not really long, and if I compare to the orignal PCB of the AVR, the tracks are similare...
Other point, when the issue appeared, I have pushed the volume for 10s (maybe 40W to the speaker), and lowered the volume. The issue appear at this point.
The cap was very hot.
The only component that I have not mounted on my PCB is capacitors between the Power Ouput and the GND (C6642 and C6652) :
In this case, C6642 is in // with the RC filter on the ouput.
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You'll need to attach a scope to the postion C5440 and see if there is any negative voltage or high frequency oscillation. You could safely put a 22 uf 400 v film cap there temporarily, but they are about $15. Sold only at speaker crossover supply houses, not general electronic supply houses. DC negative voltage means a wiring error or layout error. RF there requires further analysis of cause of oscillation.
One tipoff, the NFL line to Q5010 has no compensation cap in it. This is a very long line from the remote output zone, and beside not possibly being compensated for phase shift, could pick up RF noise, especially in a prototype outside a steel case. If RF is picked up on that line, a .1 uf ceramic cap across C5040 could be a help to damp it out. 470 uf ceramics have too much inductance to short out RF. I get AM sports talk radio on my speaker wires in organ installations, for example.
One tipoff, the NFL line to Q5010 has no compensation cap in it. This is a very long line from the remote output zone, and beside not possibly being compensated for phase shift, could pick up RF noise, especially in a prototype outside a steel case. If RF is picked up on that line, a .1 uf ceramic cap across C5040 could be a help to damp it out. 470 uf ceramics have too much inductance to short out RF. I get AM sports talk radio on my speaker wires in organ installations, for example.
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Thx all for you help.
It seems that the issue is due to oscillation, but unfortunately, I have no scope on my side for check this point :/
Other point, I remember something : I could not measures the idling current to the 0.22R resistor, when the amplifier was runing without signal, I had 0mV ! But I have not taken more measures because the amplifier was running nice and I re-used the driver with the idling current already adjusted by Onkyo...
Maybe it is a big mistake :/
It seems that the issue is due to oscillation, but unfortunately, I have no scope on my side for check this point :/
Other point, I remember something : I could not measures the idling current to the 0.22R resistor, when the amplifier was runing without signal, I had 0mV ! But I have not taken more measures because the amplifier was running nice and I re-used the driver with the idling current already adjusted by Onkyo...
Maybe it is a big mistake :/
another issue in the layout is the gnd trace entering bottom right and the speaker gnd top left. it will have probably about 100mR and the multiple gnd connection to the other board is now modulated by the speaker current, with 10A this is 100mV. This can easily cause oscillation.
To repair this solder the power supply gnd directly next to the speaker gnd.
To repair this solder the power supply gnd directly next to the speaker gnd.
OK.
I will check this tonight if there are others components dead...
Concerning the bias adjustment, if I have 0mV like yesterday, is it "dangerous" for the amplifier ? it can be the root of the issue too ?
If I can restart the amplifier tonight, I will check more precisely this point, for read arround 8-10mV, as recommended in the SM.
I will check this tonight if there are others components dead...
Concerning the bias adjustment, if I have 0mV like yesterday, is it "dangerous" for the amplifier ? it can be the root of the issue too ?
If I can restart the amplifier tonight, I will check more precisely this point, for read arround 8-10mV, as recommended in the SM.
Note that the bias circuit is in two parts. Q5410 and R5440 are on board L. The base circuit is powered by the remote Q509 (temperature sensor).
Yep, and I mounted Q509 "in" the heatsink.
Is it necessary to mount the 100nf capacitor between the output and GND, as shown in previous reply ? I have never seen a capacitor alone like that on other schematic !
Is it necessary to mount the 100nf capacitor between the output and GND, as shown in previous reply ? I have never seen a capacitor alone like that on other schematic !
Nope, I ask for the other capacitor.
https://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Onkyo-TXNR-609-Service-Manual.pdf
Chanel Left for example :
There is a RC filter with C6030 + R6130
And there is a capacitor between output and GND (C6640). I have not mounted this capacitor, is it critical ?
https://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Onkyo-TXNR-609-Service-Manual.pdf
Chanel Left for example :
There is a RC filter with C6030 + R6130
And there is a capacitor between output and GND (C6640). I have not mounted this capacitor, is it critical ?
C6642 across the output is unusual. If unit oscillates without it and not with it, it is critical. Most units have .01 uf ceramic cap series 10 to 100 ohms here, as olddiy said.
More expensive but not in these days of dead switcher supplies in every trashed appliance, a 6 to 8 turn inductor close to base lead of Q5010 (feedback) to keep RF out of it. I salvaged mine from a dead PCAT power supply. Long feedback line from outside the pcb acts as an AM radio antenna with boards out of a steel enclosure. Unit is also apparently lacking the 10 to 14 turn inductor right next to the speaker jack to keep RF out of the enclosure. That many turns 20 to 14 ga wire (20 fine for small wattage amps) wound around a china marker or AA battery, then core removed. Often parallel a 3 W 10 ohm wirewound (inductive) resistor.
Do you have a scope to check for oscillation? At least look at the exploded capacitor with a DVM to make sure a wiring error hasn't caused negative DC across it at all times.
More expensive but not in these days of dead switcher supplies in every trashed appliance, a 6 to 8 turn inductor close to base lead of Q5010 (feedback) to keep RF out of it. I salvaged mine from a dead PCAT power supply. Long feedback line from outside the pcb acts as an AM radio antenna with boards out of a steel enclosure. Unit is also apparently lacking the 10 to 14 turn inductor right next to the speaker jack to keep RF out of the enclosure. That many turns 20 to 14 ga wire (20 fine for small wattage amps) wound around a china marker or AA battery, then core removed. Often parallel a 3 W 10 ohm wirewound (inductive) resistor.
Do you have a scope to check for oscillation? At least look at the exploded capacitor with a DVM to make sure a wiring error hasn't caused negative DC across it at all times.
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I have unfortunelty no scope on my side. Concerning the output inductor, it is mounted on my PCB with 11R resistor.
I checked the components, and :
- Output transistor are dead
- Only 2SA driver is dead.
The root of the issue is maybe not the capacitor, because if the driver "2SA" (negative, so) is dead, the cap can take -62V ...
Maybe the issue is elsewhere, and destroy the output transistor and one driver ! I don't know, I'm lost -_-
I add two pics of my project :
I checked the components, and :
- Output transistor are dead
- Only 2SA driver is dead.
The root of the issue is maybe not the capacitor, because if the driver "2SA" (negative, so) is dead, the cap can take -62V ...
Maybe the issue is elsewhere, and destroy the output transistor and one driver ! I don't know, I'm lost -_-
I add two pics of my project :
What makes your scenario odd is that for a static DC fault to cause this would need one of the output devices to fail open circuit in the base/emitter path and that isn't a common failure mode. Usually transistors fail short circuit.
If one output failed open circuit (or equally a open circuit in the board/components to the base/emitter) then the amp could then fail with one of the drivers going short (as you describe) and that could apply supply voltage across the cap via the other intact driver.
Oscillation that bansuri mentions is a possibility but it would have to be bad to be a reason in itself for the cap failure.
If one output failed open circuit (or equally a open circuit in the board/components to the base/emitter) then the amp could then fail with one of the drivers going short (as you describe) and that could apply supply voltage across the cap via the other intact driver.
Oscillation that bansuri mentions is a possibility but it would have to be bad to be a reason in itself for the cap failure.
Caps can explode for a few reasons.
1/ Incorrect polarity.
2/ Too high voltage.
3/ Just a bad capacitor.
4/ Old age.
1/ Incorrect polarity.
2/ Too high voltage.
3/ Just a bad capacitor.
4/ Old age.
