Question about Line 6 Lowdown Ld150 150 Watt 1x12" Bass Combo Amp

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Low down ld150 power supply

Missing voltages

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Mixing board had all the lights come on at once and no sound


Despite the mixer's namebrand i can say that should be a low voltage supply issue, mixers have normally just 3 voltages, and the ones with effects 4, the critical voltages that mantain a mixing board working are just 2, +15V and -15V and you can check for them at Pin4 for -15V and pin8 for +15v of operational ic's at any channel with the mixer on, one of those are not present and this is you issue for sure, certain mixers have fuses for this two voltages but since you are not posting the namebrand i can't figure it out, if one voltage is missing could be the fuse or the power regulator that reads"MC7825" or "MC7915" which 7815 is for the positive rail and 7915 for the negative one, both are located in the power supply board, let me know more to help you more.

Oct 05, 2013 | Music

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I have Behringer xenyx 1622fx , It will turn on the power but a few minute the power will turn -off , Please help me to solve the problem of this unit in power supply section or other section.

Here is your schematic:

Scroll down and find link "Get manual" and click to download.. IGNORE other download links they are for third party viewers. Power supply is on page 11. This is a switching power supply running from line voltage. For personal safety USE AN ISOLATION transformer when working on it. First thing is to measure all the voltage outputs before and during shutdown. Switching power supplies often require use of an oscilloscope to repair. The three terminal regulators that follow the main switching supply each have thermal shutdown so if one of them is being overloaded it will shutdown and that voltage will drop way down. Use great caution when working on the supply!!!

Jul 20, 2012 | Behringer Xenyx 1002fx Mixer 10 Input 2...

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My Behringer XENYX 2442FX Mixer does not power up, the only light that comes on is the phantom power light. I opened it up and noticed that the switching power supply has multiple voltage outputs.

You should find +/-15 volts and probably +12 volts an +5 volts as well as the +48 phantom supply. If only one of these is missing, check the regulator for it... most are three terminal regulators. If the one that is missing has a hot regulator you have a short someplace and this requires skill to locate Probably the fastest way is to use a thermal imaging camera... however I have often used a millivoltmeter to find where the supply drops tpo near zero. Using a "calibrated" finger and search for a hot component on the circuit board can be very effective. Likely one of the surface mounted chips has shorted. Replacing these requires skill so best leave board repair to a skilled repair person as you can easily damage the board permanently.

Oct 04, 2011 | Behringer XENYX 2442FX Mixer

1 Answer

Have BBE Acousimax pre-amp. Clip light is on and will not turn off. I have not power through the unit but power source seems ok. Fuse problem?

This device, unlike most guitar pedals, requires a 12 volt power supply. Are you sure yours is the original? If the supply is low, the internal electronics will show clipping. Make sure you are using the original power supply and if so, check the voltage it is producing.

May 16, 2011 | Bbe Acoustimax Sonic MaximizerPreamp Pedal

1 Answer

The entire control board on top of the flextone III amp (volume controls, bass, treble, model selector, effects, etc..) is lit up and unresponsive. I tried a factory reset by holding a & d down for 8...

There is probably a power supply failure or with the power on reset circuit. Likely low voltage to the logic electronics. This is NOT DIY unless you are familiar with electronics.

Apr 22, 2011 | Line 6 Flextone III Plus Guitar Amplifier

1 Answer

I have a peavey valvenmaster head that was playing at very low volumes even when cranked up pretty loudly. i replaced all of the tubes with new matched groove tubes and the volume and tone improved. ...

You start by downloading the schematic here:

Scroll down to the link "Get Manual" and download the schematic. Note that it has several pages of parts list preceeding the schematic.

Next, put a 150 Watt incandescent bulb in series with the power cord to act as a current limiting fuse. Now replace the fuse and proceed with testing. You may find that one or more filter caps have shorted. Also pay particular attention the the BIAS power supply. You should see about -35 to -40 volts. Note that the series lamp will come on if excess current is being drawn and voltages will be low if the lamp lights. If the BIAS supply has failed, it is possible your power tubes have been damaged.

Mar 31, 2011 | Peavey ValveKing 100w All Tube 212 Combo...

2 Answers

I get a distorted sound from my speakers throug a Phonic Helix Board. It is connected on a PC through Fire Wire. The distortion is also there while using microphones or other inputs (CD-players etc.). It...

Hallo landgenoot ;)

It seems it is a power supply problem; distorted sound, no meters, solo buttons not working, headphones low level and distorted. One of the power supply voltages might be too low or even missing. The Helix series mixers use mainly 4 supply voltages: + 15 V and - 15 V for the analog part (audio), + 5 V for the DSP and logic and +48 V only for the phantom power. If for example the + or - 15 V is too low, clipping of the positive or negative parts of the waveform (dependng on which voltage is too low) will occur. If possible, first measure the voltages coming out of the power supply. You could use a metal part of a jack as ground reference.
For the FireWire board an extra voltage supplied by the switched PSU is used. It is specified as +12,2 V, but I measured 14 V. This voltage is lowered to + 5 V by a resistor on the FW board and a 7805 regulator. (Not very efficient!) But as far as I can see, the FW voltage is not the problem here. I have some service documentation of the Helix series mixers (12, 17 and 24, so if you need more you can conatct me: frankdevries [at]

Groeten, Frank.

Mar 18, 2011 | Phonic Helix18fw 18 Channel Mixer with...

1 Answer

Korg PA800 not booting up

I suspect you have aa pwer supply problem that is supplying low voltage to the unit. The display will light at low voltage but circuitry will not run when voltage is low.

Jul 05, 2010 | Korg Pa800 Synthesizer

1 Answer

What is the secondary voltage of power transformer

The schematics do not show the actual voltage.

From the design, the phantom power secpndary should be around 35 to 45 volts AC.

The 16 volt supplies would require a secondary winding that will be around 26 to 32 volts center tapped.

Transformers are quite reliable and unless a voltage is missing, the transformer is likely OK.

The most suspect items are the electrolytic filter caps if the voltage is not the design 16 plus and minus values.

Jun 16, 2010 | Mackie 1202vlz3 12 Channel Mixer

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