Hi, I'm a low budget PA engineer. I live with many Behringers.
As a representative player, I was using two Behringer inuke NU6000DSP.
However, one of them stopped working and remained in the protected state.
This symptom is known as the "Red Ring of Death".
Luckily, the other one is fine.
I'm using the good one as a reference to try to identify the faulty part in the faulty one
The state when the power is turned on is as follows.
A normal inuke will make two relay clicks on start up.
A faulty inuke will make one relay click on start up.
The large relay near the power plug is not working.
I found the circuit diagram of Inuke NU6000DSP online.
And, I am currently comparing the voltage of a normal inuke with the voltage of a faulty inuke,
comparing the resistance value of a normal inuke with the resistance value of a faulty inuke,
etc.
If there is a big difference between the two,
I would be able to determine that the point of difference is faulty,
or at least is affected by a fault.
Below are the major differences I have found so far.
From this information, can you identify the cause of this failure?
The voltage on the ±83V line is abnormally low.
A normal product had a voltage of ±84V,
while the faulty product had a voltage of around ±3V.
I also measured the voltage and resistance from the COM pin to each major pin on IC16 to IC-19 (IRS20957S).
The results were:
Normal Inuke
COM to VCC
About 11.8V
COM to VDD
About 94.9V
COM to CSD
About 94.5V
COM to VDD (resistance)
About 0.8MΩ
Faulty Inuke
COM to VCC
About 11.8V
COM to VDD
IC16 7.4V
IC17 6.9V
IC18 6.9V
IC19 7.4V
COM to CSD
About 7.1V
COM to VDD (resistance)
About 25KΩ
A typical cause of failure in the Behringer inuke series seems to be a shorted diode,
but in my case, none of the main diodes were shorted.
The diodes that I confirmed were not shorted are as follows.
d10
d13
d14
d15
d20
d22
d25
d26
d27
d28
d29
d30
d31
d32
D37
D38
D39
D40
D41
There were also no shorts in the large electrolytic capacitors.
Below are the capacitors that were confirmed to have no shorts.
C5
C11
C23
C34
C48
C49
C60
C61
C62
C69
C70
C71
C154
C155
C156
C157
There are many reports of inuke series failures on the Internet, but my case may be a rare failure.
As far as I have checked, there are no shorts in any diodes.
Anyway, it is certain that a voltage drop is occurring on the ±83V line.
However, I do not know what is causing this phenomenon.🥶
I would appreciate it if you could give me some ideas to verify this using a normal inuke as a reference.
Finally, I have experience repairing tube guitar amplifiers, but this is my first time repairing a digital power amplifier for PA.
So, it is my first time dealing with such small parts.😱
I do not want to remove parts from the board randomly.
I want to remove parts only after I know which parts are broken.
To do this, I would like to know a way to determine the problem area without removing the parts.
Thank you in advance.
As a representative player, I was using two Behringer inuke NU6000DSP.
However, one of them stopped working and remained in the protected state.
This symptom is known as the "Red Ring of Death".
Luckily, the other one is fine.
I'm using the good one as a reference to try to identify the faulty part in the faulty one
The state when the power is turned on is as follows.
A normal inuke will make two relay clicks on start up.
A faulty inuke will make one relay click on start up.
The large relay near the power plug is not working.
I found the circuit diagram of Inuke NU6000DSP online.
And, I am currently comparing the voltage of a normal inuke with the voltage of a faulty inuke,
comparing the resistance value of a normal inuke with the resistance value of a faulty inuke,
etc.
If there is a big difference between the two,
I would be able to determine that the point of difference is faulty,
or at least is affected by a fault.
Below are the major differences I have found so far.
From this information, can you identify the cause of this failure?
The voltage on the ±83V line is abnormally low.
A normal product had a voltage of ±84V,
while the faulty product had a voltage of around ±3V.
I also measured the voltage and resistance from the COM pin to each major pin on IC16 to IC-19 (IRS20957S).
The results were:
Normal Inuke
COM to VCC
About 11.8V
COM to VDD
About 94.9V
COM to CSD
About 94.5V
COM to VDD (resistance)
About 0.8MΩ
Faulty Inuke
COM to VCC
About 11.8V
COM to VDD
IC16 7.4V
IC17 6.9V
IC18 6.9V
IC19 7.4V
COM to CSD
About 7.1V
COM to VDD (resistance)
About 25KΩ
A typical cause of failure in the Behringer inuke series seems to be a shorted diode,
but in my case, none of the main diodes were shorted.
The diodes that I confirmed were not shorted are as follows.
d10
d13
d14
d15
d20
d22
d25
d26
d27
d28
d29
d30
d31
d32
D37
D38
D39
D40
D41
There were also no shorts in the large electrolytic capacitors.
Below are the capacitors that were confirmed to have no shorts.
C5
C11
C23
C34
C48
C49
C60
C61
C62
C69
C70
C71
C154
C155
C156
C157
There are many reports of inuke series failures on the Internet, but my case may be a rare failure.
As far as I have checked, there are no shorts in any diodes.
Anyway, it is certain that a voltage drop is occurring on the ±83V line.
However, I do not know what is causing this phenomenon.🥶
I would appreciate it if you could give me some ideas to verify this using a normal inuke as a reference.
Finally, I have experience repairing tube guitar amplifiers, but this is my first time repairing a digital power amplifier for PA.
So, it is my first time dealing with such small parts.😱
I do not want to remove parts from the board randomly.
I want to remove parts only after I know which parts are broken.
To do this, I would like to know a way to determine the problem area without removing the parts.
Thank you in advance.
See rectifier.
Check SMPS if any, sometimes bad SMPS chip is responsible.
Also may be bad relay contact.
Start with basics, see the AC volts from transformer to rectifier.
Did not read post fully, just scanned.
May have missed details.
Check SMPS if any, sometimes bad SMPS chip is responsible.
Also may be bad relay contact.
Start with basics, see the AC volts from transformer to rectifier.
Did not read post fully, just scanned.
May have missed details.
Thank you for the information.👍
Next, I will focus on finding the problem in that area.
By the way, I don't have any friends, so I consulted an AI about this problem.💻
Below is Google Gemini's reasoning on this problem and the suspected faulty parts.
I would also like to hear what you humans think about this AI's reasoning. Thank you.
-----------
Summary and Reasoning for Identifying the Faulty Part in Behringer iNuke NU6000DSP Power Supply Unit
Device: Behringer iNuke NU6000DSP Power Amplifier
Main Symptom: The amplifier powers on, but protection does not disengage, and the final output voltage (±83V rails) is only around ±3V. The second click from the soft-start relay (RLY1) is not heard.
1. Initial Diagnostics and PSU Primary DC Bus Voltage Check:
Whether the load connector (X5) to the amplifier modules was connected or disconnected, the main high-voltage DC bus on the PSU primary side was measured to be stable: approx. +280V for the normal unit, and approx. +283V to +284V for the faulty unit.
This indicated that the basic DC voltage generation (AC input rectification, main filter capacitors) on the primary side was largely functional in the faulty unit.
However, in the faulty unit, RLY1 did not engage, and the final ±83V output remained at ~±3V.
2. Control IC Status Check:
The main power supply controller was identified as IC3 (KA3525A), and a timer IC controlling its shutdown was identified as IC2 (NE555D).
IC3 (KA3525A) Pin 10 (Shutdown): Measured 5.2V (High) in the faulty unit, and 4.7V (High) in the normal unit. This suggested a shutdown state in both units (though possibly a normal standby state for the normal unit under test conditions).
IC2 (NE555D) Pin 3 (Output): Measured 3.7V (High) in the faulty unit, and 0.3mV (Low) in the normal unit. Since IC2's output is connected to IC3's Shutdown pin, IC2 was determined to be shutting down IC3 in the faulty unit.
IC2 (NE555D) Pin 2 (Trigger): Measured 0.82V (Low) in the faulty unit, versus 4.6V (High) in the normal unit. This low voltage on Pin 2 was causing IC2's Output (Pin 3) to go High.
Other IC2 (NE555D) Pin Voltages:
VCC (Pin 8): 5.0V (Normal), 5.0V (Faulty) ? Power OK.
Reset (Pin 4): 5.0V (Normal), 5.0V (Faulty) ? Reset not active, OK.
Threshold (Pin 6): 8mV (Normal), 1.3V (Faulty).
Control (Pin 5): 3.3V (Normal), 3.4V (Faulty).
3. Investigation into the Low Voltage at IC2 Pin 2 (Trigger):
Various components connected to the IC2 Pin 2 node were investigated:
IC1 (Comparator) Outputs (via D9): IC1 Pin 13 & 14 voltages were -9.7V (Normal) and -14.1V (Faulty) (ref IC1 Pin 12 GND). Regardless of polarity ambiguity, these were not LOW, thus not the cause of IC2 Pin 2 being pulled low via D9.
D42 Path: D42 cathode voltage was ~14.4V (Normal) and ~15.0V (Faulty). D42 was reverse-biased, not pulling IC2 Pin 2 low.
Resistance from IC2 Pin 2 Node to GND: Measured ~5.9kΩ and was identical in both normal and faulty units, suggesting no abnormal leakage to ground.
Pull-up/Pull-down Resistors:
R23 (47kΩ): Pull-down from IC2 Pin 2 to GND. In-circuit check consistent between units.
R26 (392kΩ): Pull-up from IC2 Pin 2 to "Pull-up Source Node" (IC1-A Pin 5, etc.). In-circuit check suggested R26 itself was not open.
"Pull-up Source Node" (IC1-A Pin 5) voltage: 7.8V (Normal), 7.4V (Faulty) ? No significant difference.
Capacitors C24, C27 (on IC2 Pin 2 node): Resistance checks showed no shorts and similar behavior between units.
Transistor T4 (PNP MMBT3906): Base connected to IC2 Pin 2. Determined to be turned ON as a result of IC2 Pin 2 being low, not the cause.
4. Detailed Investigation of Transistor T9 (NPN 3904):
T9's Collector connects to IC2 Pin 2; Emitter to GND. T9 can pull IC2 Pin 2 LOW if ON.
T9 Base Voltage Anomaly (Faulty Unit):
"Node T9-Base-Drive" (driving T9 base via R82=10kΩ): 0.21V
T9 Base pin (output side of R82): 0.64V
Resistance of R82 (10kΩ) confirmed OK.
Voltage drop across R82: 0.43V in the faulty unit (0.64V - 0.21V), versus 0V in the normal unit. This implies an abnormal current of ~43μA flowing out of T9's base backwards through R82.
AC Voltage Check: No significant AC component found at T9 base or its driving node, suggesting DC readings are reliable.
T9 Diode Checks (Faulty vs. Normal):
Base-Emitter Forward: 0.66V (N) vs 0.66V (F) ? OK.
Base-Emitter Reverse: 1.96V stable (N) vs ~1.4V unstable (F) ? Abnormal.
Base-Collector Forward: 0.65V (N) vs 0.64V (F) ? OK.
Base-Collector Reverse: 1.98V stable (N) vs ~0.93V unstable (F) ? Abnormal.
Checks on components around T9 base driving node (C80, D48): No significant differences found. C81 (T9 B-E) also checked okay.
5. Reasoning and Conclusion:
The significant degradation of T9's reverse junction characteristics (B-E and B-C) was confirmed.
In operation, T9's base exhibits an abnormal voltage (0.64V) higher than its driving node (0.21V), suggesting current is sourcing from the base or an internal fault.
This 0.64V on T9's base is sufficient to partially turn T9 ON.
A partially ON T9 pulls its collector (the IC2 Pin 2 node) down to the measured 0.82V.
The low voltage (0.82V) on IC2 Pin 2 causes IC2's output (Pin 3) to go high.
IC2's high output drives IC3's Shutdown pin (Pin 10) high, disabling the main controller.
This results in RLY1 not engaging and no ±83V output.
Predicted Faulty Component: Internal failure of Transistor T9 (3904 NPN).
Proposed Action: Replace T9.
--------
Next, I will focus on finding the problem in that area.
By the way, I don't have any friends, so I consulted an AI about this problem.💻
Below is Google Gemini's reasoning on this problem and the suspected faulty parts.
I would also like to hear what you humans think about this AI's reasoning. Thank you.
-----------
Summary and Reasoning for Identifying the Faulty Part in Behringer iNuke NU6000DSP Power Supply Unit
Device: Behringer iNuke NU6000DSP Power Amplifier
Main Symptom: The amplifier powers on, but protection does not disengage, and the final output voltage (±83V rails) is only around ±3V. The second click from the soft-start relay (RLY1) is not heard.
1. Initial Diagnostics and PSU Primary DC Bus Voltage Check:
Whether the load connector (X5) to the amplifier modules was connected or disconnected, the main high-voltage DC bus on the PSU primary side was measured to be stable: approx. +280V for the normal unit, and approx. +283V to +284V for the faulty unit.
This indicated that the basic DC voltage generation (AC input rectification, main filter capacitors) on the primary side was largely functional in the faulty unit.
However, in the faulty unit, RLY1 did not engage, and the final ±83V output remained at ~±3V.
2. Control IC Status Check:
The main power supply controller was identified as IC3 (KA3525A), and a timer IC controlling its shutdown was identified as IC2 (NE555D).
IC3 (KA3525A) Pin 10 (Shutdown): Measured 5.2V (High) in the faulty unit, and 4.7V (High) in the normal unit. This suggested a shutdown state in both units (though possibly a normal standby state for the normal unit under test conditions).
IC2 (NE555D) Pin 3 (Output): Measured 3.7V (High) in the faulty unit, and 0.3mV (Low) in the normal unit. Since IC2's output is connected to IC3's Shutdown pin, IC2 was determined to be shutting down IC3 in the faulty unit.
IC2 (NE555D) Pin 2 (Trigger): Measured 0.82V (Low) in the faulty unit, versus 4.6V (High) in the normal unit. This low voltage on Pin 2 was causing IC2's Output (Pin 3) to go High.
Other IC2 (NE555D) Pin Voltages:
VCC (Pin 8): 5.0V (Normal), 5.0V (Faulty) ? Power OK.
Reset (Pin 4): 5.0V (Normal), 5.0V (Faulty) ? Reset not active, OK.
Threshold (Pin 6): 8mV (Normal), 1.3V (Faulty).
Control (Pin 5): 3.3V (Normal), 3.4V (Faulty).
3. Investigation into the Low Voltage at IC2 Pin 2 (Trigger):
Various components connected to the IC2 Pin 2 node were investigated:
IC1 (Comparator) Outputs (via D9): IC1 Pin 13 & 14 voltages were -9.7V (Normal) and -14.1V (Faulty) (ref IC1 Pin 12 GND). Regardless of polarity ambiguity, these were not LOW, thus not the cause of IC2 Pin 2 being pulled low via D9.
D42 Path: D42 cathode voltage was ~14.4V (Normal) and ~15.0V (Faulty). D42 was reverse-biased, not pulling IC2 Pin 2 low.
Resistance from IC2 Pin 2 Node to GND: Measured ~5.9kΩ and was identical in both normal and faulty units, suggesting no abnormal leakage to ground.
Pull-up/Pull-down Resistors:
R23 (47kΩ): Pull-down from IC2 Pin 2 to GND. In-circuit check consistent between units.
R26 (392kΩ): Pull-up from IC2 Pin 2 to "Pull-up Source Node" (IC1-A Pin 5, etc.). In-circuit check suggested R26 itself was not open.
"Pull-up Source Node" (IC1-A Pin 5) voltage: 7.8V (Normal), 7.4V (Faulty) ? No significant difference.
Capacitors C24, C27 (on IC2 Pin 2 node): Resistance checks showed no shorts and similar behavior between units.
Transistor T4 (PNP MMBT3906): Base connected to IC2 Pin 2. Determined to be turned ON as a result of IC2 Pin 2 being low, not the cause.
4. Detailed Investigation of Transistor T9 (NPN 3904):
T9's Collector connects to IC2 Pin 2; Emitter to GND. T9 can pull IC2 Pin 2 LOW if ON.
T9 Base Voltage Anomaly (Faulty Unit):
"Node T9-Base-Drive" (driving T9 base via R82=10kΩ): 0.21V
T9 Base pin (output side of R82): 0.64V
Resistance of R82 (10kΩ) confirmed OK.
Voltage drop across R82: 0.43V in the faulty unit (0.64V - 0.21V), versus 0V in the normal unit. This implies an abnormal current of ~43μA flowing out of T9's base backwards through R82.
AC Voltage Check: No significant AC component found at T9 base or its driving node, suggesting DC readings are reliable.
T9 Diode Checks (Faulty vs. Normal):
Base-Emitter Forward: 0.66V (N) vs 0.66V (F) ? OK.
Base-Emitter Reverse: 1.96V stable (N) vs ~1.4V unstable (F) ? Abnormal.
Base-Collector Forward: 0.65V (N) vs 0.64V (F) ? OK.
Base-Collector Reverse: 1.98V stable (N) vs ~0.93V unstable (F) ? Abnormal.
Checks on components around T9 base driving node (C80, D48): No significant differences found. C81 (T9 B-E) also checked okay.
5. Reasoning and Conclusion:
The significant degradation of T9's reverse junction characteristics (B-E and B-C) was confirmed.
In operation, T9's base exhibits an abnormal voltage (0.64V) higher than its driving node (0.21V), suggesting current is sourcing from the base or an internal fault.
This 0.64V on T9's base is sufficient to partially turn T9 ON.
A partially ON T9 pulls its collector (the IC2 Pin 2 node) down to the measured 0.82V.
The low voltage (0.82V) on IC2 Pin 2 causes IC2's output (Pin 3) to go high.
IC2's high output drives IC3's Shutdown pin (Pin 10) high, disabling the main controller.
This results in RLY1 not engaging and no ±83V output.
Predicted Faulty Component: Internal failure of Transistor T9 (3904 NPN).
Proposed Action: Replace T9.
--------
"A fault in T9 → Abnormal trigger voltage for IC2 → IC2's output goes High → IC3 shuts down → This results in the ±83V rail voltage drop."
In a nutshell, this is Gemini's reasoning.
I would be happy if you could confirm that there are no contradictions in this.
And these are the voltages and resistances at various points that I measured while talking to the AI.
Here you can see where the numerical difference is between a normal unit and a faulty unit.
This table was also automatically compiled by the AI. What a great job.
https://docs.google.com/spreadsheet...iUUfxxy461RAe6HUsIfUJxu7b_wvc3wMls9XK/pubhtml
In a nutshell, this is Gemini's reasoning.
I would be happy if you could confirm that there are no contradictions in this.
And these are the voltages and resistances at various points that I measured while talking to the AI.
Here you can see where the numerical difference is between a normal unit and a faulty unit.
This table was also automatically compiled by the AI. What a great job.
https://docs.google.com/spreadsheet...iUUfxxy461RAe6HUsIfUJxu7b_wvc3wMls9XK/pubhtml