behringer v ampire voltage supply to pre amp?

[tinny]

hi guys
I've picked up faulty behringer guitar combo LX210 V ampire as a repair project in my retirement and as my field of work was telecommunications I have virtually no experience working on this type of equipment.
So I was hoping someone could kindly point me in the right direction.
The amp turns on ok front panel lights up but when guitar is plugged in o/p is barely audible and only bass freqs.
I have plugged a drum machine into line in jack on rear panel and signal out is loud and clear
I have measured the voltages on the secondary windings of the transformer which brings me to my first question
The secondary winding voltage connected to what I think is the pre amp cct board is approx 10.6 v is that too low ?
I have searched for a schematic or any information on this amp but so far without luck
thank you
ps I have no test gear apart from a digital multimeter

[Mick Bailey]

Try patching the FX send to FX return and then try it. The amp uses a serial FX loop, so all the signal passes through the switching contacts and if dirty these will attenuate the signal. Patching eliminates the switching contacts.

10.6v seems to be off to me - I would have expected a dual supply to the preamp, something like +/-15v for any opamps, as well as 5v or 3.3v for the processors (perhaps regulated down from a positive opamp supply) A clue to the voltages will be what voltage regulators are fitted - take a closer look at the board. Also, any IC part numbers will show the operating voltages in their spec sheets.

[eschertron]

Does this amp have a headphone out? This may help determine if the problem is in the preamp.

[tinny]

Try patching the FX send to FX return and then try it. The amp uses a serial FX loop, so all the signal passes through the switching contacts and if dirty these will attenuate the signal. Patching eliminates the switching contacts.

10.6v seems to be off to me - I would have expected a dual supply to the preamp, something like +/-15v for any opamps, as well as 5v or 3.3v for the processors (perhaps regulated down from a positive opamp supply) A clue to the voltages will be what voltage regulators are fitted - take a closer look at the board. Also, any IC part numbers will show the operating voltages in their spec sheets.

i have tried the FX send to FX return result no out put which leads me to believe the fault is between guitar i/p jack and pre amp o/p
I have checked all jacks on front and rear of amp they appear in good condition but i sprayed them with contact cleaner just in case

the transformer has 3 secondary windings 2 have centre taps voltages are 17.2 v +/- and 26.2v +/- no idea if that is good or not but they connect to board which i think is o/p amp ??? which is working
the third secondary winding measured at around at 10v which is the one I suspect maybe out of spec

I have checked the head phone jack dead unfortunately

thanks guys thats given me some ideas looks like I may have the boards mixed up but still not sure if voltges are correct

[sugeda]

https://www.docdroid.net/5MjgyZ5/lx210-pdf

[g1]

Transformer windings will be AC volts. Supplies to preamp will be DC volts.

[tinny]

thank you so much a great help

[Mick Bailey]

The drum machine in the line in works loud and clear, so that tells us the +/-15v supplies are fine, as well as the main supply rails to the power amp, otherwise there would be no sound. The only other DC voltages are +5v and +3.3v for the processor and logic side of things. If the amp will scroll through and recall patches, then these supplies are also fine. Check the operation to see if this is the case. If all that works, then the all the DC voltages are OK.

[tinny]

The drum machine in the line in works loud and clear, so that tells us the +/-15v supplies are fine, as well as the main supply rails to the power amp, otherwise there would be no sound. The only other DC voltages are +5v and +3.3v for the processor and logic side of things. If the amp will scroll through and recall patches, then these supplies are also fine. Check the operation to see if this is the case. If all that works, then the all the DC voltages are OK.

yes i think that is all working front panel lights up and appears to be ok, selecting patches looks ok but sound is very very low at first I thought it was completely dead and no treble at all so from what you are saying maybe I should start again at the input jack
and completely dismantle it or plug in drum machine and see how far I can follow it
thanks for your help mick I'll keep at it

[The Dude]

I would also restore/reset the unit to factory default settings. It's possible you just have some corrumpt data. From the manual:

"All factory presets can be restored as follows: Hold down
buttons D and E and then switch on the device. "CL"
appears in the display. Now release the two buttons and press
the two arrow buttons simultaneously. This erases all the edited
presets you have stored and restores the factory presets."

[tinny]

awesome i checked it wasnt in some weird mode but I didnt try factory default settings. I will re assemble it tonight and give it a go
thanks mate

[tinny]

https://www.docdroid.net/5MjgyZ5/lx210-pdf

thank you sugeda its helped already

[Mick Bailey]

If you have no improvement with a factory reset an audio probe is useful in tracing a signal through the audio path. It's simple to make and very effective, though you need another basic amplifier to use it with. I have a cheap starter amp that I use for such purposes, though pretty much anything will work. A side project could be to build a self-contained amplifier using an LM386 and small speaker from an old radio.

[tinny]

If you have no improvement with a factory reset an audio probe is useful in tracing a signal through the audio path. It's simple to make and very effective, though you need another basic amplifier to use it with. I have a cheap starter amp that I use for such purposes, though pretty much anything will work. A side project could be to build a self-contained amplifier using an LM386 and small speaker from an old radio.

thanks mick yes the factory reset made no difference so next job is to follow the signal path, i've got an old cheap amp that will be suitable .cheers john