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Behringer Inuke NU1000 not powering on.
Behringer Inuke NU1000 not powering on.
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Old 10th February 2014, 09:56 PM   #1
Paulmongan is offline Paulmongan  Ireland
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Default Behringer Inuke NU1000 not powering on.

Hi everyone,

This is my first post, I hope someone out there can help me.

I have a Behringer iNuke NU1000 class D power amp that's not powering up. I have spent a good amount of time on it now and cannot find the fault. I can't find a schematic diagram for it anywhere on line. I contacted Behringer they give me no information at all.


When powered on I have 240V AC up to the Bridge Rectifier, 330V DC out of Bridge Rect into smoothing caps.
Voltage at smoothing caps, 329V & 163V. The caps are in series 1500uF @ 200V each, both testing good on Peak atlas ESR tester.

large TX is getting 163V.
Power Transistor on right in picture is receiving 330V on the drain (centre pin 2) with no voltage on gate & source. Source of this trans is connected to Drain of left power Trans.
Power Transistor on left in picture has 0V on all pins.

VIPer22A Current mode PWM controller is getting
7V on VDD (switched off). According to data sheet it needs to be typically 14.5V at which the device starts switching.

KA3525A Pulse width modulating regulator has no voltage at any of the 16 pins.

I replaced VIPer22A primary switcher, KA3525a pulse width modulating regulator and both power transistors 6R199P and still no joy. I tested all components on the primary & secondary side of the board mainly looking for shorts and all seem to test good.


The unit is about 2 years old and was installed in a primary school where it was probably power cycled for use with volume level full on and switch in on position.


If anyone can give me any advice at all, I will be delighted.

Thanks
Paul
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Old 12th February 2014, 01:45 AM   #2
kASD is offline kASD
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Why do you have removed the white colored relay?
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Old 12th February 2014, 10:00 AM   #3
Paulmongan is offline Paulmongan  Ireland
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Hi workhorse,

Thanks for reply. From my research the white coloured relay is not fitted on the Inuke NU1000. The pictures where taken before any troubleshooting began. I bought the amp new so I know nobody else has worked on it.

I attach a picture of a Behringer Inuke NU3000. It has the Relay you describe in place. If this relay was faulty then no voltage would be present on caps.

Regards,
Paul
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Old 13th February 2014, 12:57 PM   #4
Khron is offline Khron  Finland
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I'm gonna hazard a guess, and say that the trouble may well be in the stand-by section of the power circuit.

If the ViPer22 isn't powered/working, nothing is. I'd point my attention to the so-called "start-up cap", which is filtering the Vcc rail of the ViPer22. That should be (replaced with) a low-ESR cap from a reputed (Japanese) brand, of similar value and voltage rating.

After that (or if that doesn't revive the thing), i'd direct my investigation towards the secondary of the stand-by section, particularly the caps on the rail from which feedback is taken. In ATX power supplies, dying / dead caps on the secondary can (and do) screw up the feedback signal, which makes the associated primary section go a bit haywire.

PS: I've got a hunch that relay on the NU3000 is there just to bypass the thermistor, after a certain delay. So with or without the relay, you'd still have voltage across the primary caps

Last edited by Khron; 13th February 2014 at 12:58 PM. Reason: PS.
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Old 13th February 2014, 01:12 PM   #5
Paulmongan is offline Paulmongan  Ireland
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Hi khron,
Thank you for the information. . I'll try that later on this evening.

Regards,
Paul
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Old 14th February 2014, 03:17 AM   #6
kASD is offline kASD
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Try checking SMD resistors around Viper, VAC across viper bulk cap. Viper secondary side, also check for shorted components on secondary of viper transformer.
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Old 16th February 2014, 07:13 PM   #7
Paulmongan is offline Paulmongan  Ireland
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Hi Workhorse,

Thanks for your advice, I've been away all week end, I hope to get back to it soon. I've ordered some more new parts as Khron advised. I will keep your advice in mind when I get to it again. I will keep you all posted.

Many thanks
Paul
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Old 18th February 2014, 11:17 PM   #8
Paulmongan is offline Paulmongan  Ireland
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Hi everyone,

I have changed all 17 electrolytic caps around VIPer with exact same value Panasonic low ESR type. I used surface mount instead of SMD just because I don't like SMD caps. I have checked all SMD resistors in the board and I am getting sensible readings. All diodes check good too. I am still not getting any power up

I notice pins 2 & 3 on VIPer ( source & feedback are connected with a small SMD cap. I tried to measure the capacitance of this but was unsuccessful. I measure 1.7K across it both ways with no charging effect. I would like to change this component but have no values.
Pins 5 to 8 on VIPer each have 220V dc.. VDD is still around 7v dc..



Paul
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Old 19th February 2014, 12:54 AM   #9
Khron is offline Khron  Finland
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SMD = Surface Mounted Device; did you mean you replaced the original surface-mounted caps with through-hole (ie. legged) ones?

http://www.st.com/web/en/resource/te...CD00087939.pdf

The link above is the datasheet to the ViPer 22A. On page 11 there's some details about the start-up sequence. The second paragraph on that page caught my eye:

"Note that during the real starting phase tss, the device consumes some energy from the VDD capacitor, waiting for the auxiliary winding to provide a continuous supply. If the value of this capacitor is too low, the start up phase is terminated before receiving any energy from the auxiliary winding and the converter never starts up."

Also, see the schematic at page 7? See if you can find which components on the power supply board correspond to R1, C2 and D1 (which comprise the RCD snubber / clamp, across the transformer's primary). I've seen a couple of such flyback psu's "killed" by sub-specced snubber components.

PS: You're measuring 220v *DC* from pins 5-8, relative to what? As in, your black (negative) multimeter probe is connected to... what? Ireland has a 230V AC network, doesn't it? That should translate to something in the region of 315-325V DC after rectification. Perhaps it might be worth checking the rectifier bridge as well?
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Old 19th February 2014, 10:48 PM   #10
Paulmongan is offline Paulmongan  Ireland
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A picture of the components on the power supply board corresponding to R1, C2 and D1 from VIPer22A spec...(which comprise the RCD snubber / clamp, across the transformer's primary).

http://www.st.com/web/en/resource/te...CD00087939.pdf

Ps thanks for the link Khron
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