Repair - Behringer X32 doesn't boot

May 24, 2017

For a couple of months now, my Behringer X32 had some booting issues. By turning the unit off and on again a couple of times, it would boot properly after some time. So I ignored the issue until yesterday when the unit seemed to be completely dead.

Because the unit was working correctly after a successful booting process, I suspected a power sequencing problem at first.

Inside the Behringer X32 Rack, the PSU is on a separate PCB in the right front. To take it out, four screws have to be removed.

Before starting the repair, I tried to find a service manual for the Behringer X32 Rack, but I could only find one for the regular Behringer X32 mixing console. Although the PSU in the rack version seems to be different, the processor board is the same. This is helpful because now I know what the voltages going to the processor board should be.

As far as I know, the voltages should be as follow:

• Pin 1: Should be 48V; Measured 35V
• Pin 2: Should be -16V; Measured -12V
• Pin 3: GND
• Pin 4: GND
• Pin 5: Should be 6V; Measured 4V
• Pin 6: Same as Pin 5
• Pin 7: Should be 16V; Measured 12V

Because the voltages are all low by about 30%, the problem is likely caused by the feedback loop for the control circuit of the flyback converter.

A common issue with this type of power supply is the degradation over time of an electrolytic capacitor in the control circuit of the PSU. This leads to a decreased output voltage or prevents the PSU from turning properly on at all.

After locating this capacitor, I replaced it with a new one. In this case, it was a 47µF / 35V.

After replacing the capacitor, the output voltages were as follows:

• Pin 1: Should be 48V; Measured 42V
• Pin 2: Should be -16V; Measured -14.7V
• Pin 3: GND
• Pin 4: GND
• Pin 5: Should be 6V; Measured 5.1V
• Pin 6: Same as Pin 5
• Pin 7: Should be 16V; Measured 14.7V

So the voltages are still a bit (10%) too low, but much better than before.

After thinking about that, I decided to give it a try and tested the PSU together with the rest of the X32.

And it worked. Now it only has to be assembled again.

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It's not over yet

May 12, 2020

Three years have passed since I originally wrote this article. Unfortunately, the issues started to appear again.

This time some of the 1000µF / 25V output capacitors failed.

It's hard to see in the picture, but the capacitors inside the blue circle started leaking.

At this point, I would recommend replacing all the electrolytic capacitors.

The table below lists all their values and quantities:

Quantity	Capacitance	Voltage
5	1000µF	25V
1	470µF	25V
2	470µF	16V
1	330µF	400V
1	220µF	100V
2	47µF	63V
2	47µF	35V

Preferably, Low ESR capacitors should be used for all but the 330µF / 400V capacitor.

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R4 - Another common failure mode

I received multiple messages from people who had to replace the R4 NTC resistor.

The measured cold value of this resistor in my X32 is 10 Ohm.

After some further investigation I found that the NTC used in the X32 console (non-Rack) is a THINKING SCK15056MSY.

The datasheet of the series can be found here.

Thanks to somebody who contacted me about this issue, I can now say that the original part was likely a THINKING SCK10103.

The exact specification for a replacement part is: 10mm diameter, 10 Ohms, 3A.

What is R4 for anyway?

The purpose of R4 is to limit the current to the bulk capacitor (the big one in the middle) when the unit is turned on. It acts as what is called an "Inrush current limiter". Because the bulk capacitor is empty at the time of turn-on, it would draw a high current (called inrush current) otherwise. Being an NTC, R4 will conduct better (lower resistance) as soon as it gets warm. The value of 10 Ohms is only applicable while it is cold. Once it is heated up the resistance will drop to close to 0 ohms.

Without the initial resistance of R4, the PSU would cause a very high current spike (10s or even 100s of amps) every time it is turned on. The full-bridge rectifier inside the PSU would age dramatically from the high current surges and eventually die. Interference with other devices connected to the electrical grid is also possible. Maybe it would even trip the circuit breaker / fuse of the electrical installation.

R4 has therefore a very important role in the PSU.

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D5 - And Another One

February 19, 2022

I was contacted about another new failure mode of the X32 Rack PSU - This time it is the diode D5.

Thanks to Greg for providing the following description (slightly edited by me):

Fault symptom

An audible mechanical 'click' ( ie not through speakers) and all XLR inputs and outputs stopped working (ie all mic inputs and the main outputs to the amp). The front panel display and Jack inputs and outputs were still working (ie instruments on and monitor outs). To the best of my knowledge, the phantom power was off to all mics, but I wasn't there at the time and cannot be 100% certain.

Fault finding

The diode D5 on the PSU PCB had split in half. Fortunately, its description code was visible - SR360. 

Visual inspection of the PSU found nothing else. All electrolytic capacitors appeared normal.

Repair

I replaced D5.

Test

I powered it up and all appears to be functioning correctly!

For now!

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IC2 - PWM Controller

January 3, 2023

Some people have reported issues with the control IC.

The marking on the IC is "200D6" which suggests that the used controller is probably the NCP1200 from ON-Semiconductor.

The datasheet can be found here.

Even if your controller IC is not broken, reading and understanding this datasheet is a good starting point for troubleshooting the PSU.

 

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Schematic

 Oktober 8, 2023

The below schematic was reverse-engineered and sent to me by somebody else who wanted to remain anonymous. It is likely to contain some errors!

The pdf version of the schematic can be downloaded here: Schematic Download.

 

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