Behringer v tone problem

[izzybell2810]

Hi,
is anyone here familiar with the Behringer V tone? I've been asked to repair one for a friend. The amp powers up but there's no sound. The Power amp section is fine there is sound if I plug into the insert jacks, I get nothing from the effects loop return tho. I've checked what seems to be a small pre amp attached to the input jack and all connections (can't imagine one of those connectors going down with the ammount of hot melt on them.)

Cheers

[Enzo]

YOu mean you get nothing from the effects loop send. It would be normal to get no output from the loop return.


I'd have to look up the V tone, don;t know it. But first place I'd look would be the low voltage power rails for the preamp. I assume +/-15v, but maybe +/-12. Check at some op amp in the middle of the board. Now apply a signal to the input and trace it. I know, there are no schematics. But look at each op amp on the board and see if the output pins have DC on them, usually shouldn't. And is there signal on those outputs?

Put a scope on each output and touch the associated input pins with a meter probe or something. There should be a resulting click or hum.

[izzybell2810]

Thanks for the reply Enzo,
I've checked the voltage power rails and they're just under 11 volts. Unfortunatly I don't have a scope, but I'll be taking it to a friends tomorrow to use his. There are 6 B9QU438 op amps on the double sided board which is a proper eye strain to look at as the components are so small.

This is Behringers discription of the amp:
V-TONE GMX212

True Analog Modeling 2 x 60-Watt Stereo Guitar Amp with 2 Independent Channels, each Featuring 27 Modeled Sounds, FX Processor, Tuner and MIDI Control

The V-TONE GMX212 is the flagship in the V-TONE guitar amp series with 2 x 60 Watts, featuring two 12in JENSEN / BUGERA speakers and authentic V-TONE analog modeling combined with integrated multi-effects and tuner. The GMX212 offers two full-featured modeling channels that boast 3 classic guitar amps, 3 speaker simulation models plus 3 gain modes each—all individually selectable. Ultra-flexible FXT function allows independent effects settings on each channel, while the patented DYNAMIZER circuitry captures every nuance of your playing and lends tube-like compression to your tone. The 24-bit stereo multi-effects processor with world-class effects such as chorus, flanging, phasing, rotary, auto-wah, echo, delay , compressor and various effect combinations offers 99 user presets and MIDI control. The integrated auto-chromatic tuner is controllable via footswitch.

[Enzo]

AH, it's a GMX212.

"V-tone" is not specific - that is like calling your car a GM car, not very specific.

11v is pretty low, the op amp circuits run on +/-15 The 15v rails come from three-leg regulators on the heat sink. Are any of the ICs getting HOT to the touch? Disconnect the preamp card - do the 15s come back up? Disconnect the jack board on the rear - this amp has one doesn;t it? If so, do the 15s come back up then? I am hunting here for something loading down those supplies. In my experience it wil be the TL074 on the rear jack board, but we'll see.

All those op amps are 4580 for the dual and TL074 for the quads.

Does the tape in register an output?

[izzybell2810]

AH, it's a GMX212.

"V-tone" is not specific - that is like calling your car a GM car, not very specific.

11v is pretty low, the op amp circuits run on +/-15 The 15v rails come from three-leg regulators on the heat sink. Are any of the ICs getting HOT to the touch? Disconnect the preamp card - do the 15s come back up? Disconnect the jack board on the rear - this amp has one doesn;t it? If so, do the 15s come back up then? I am hunting here for something loading down those supplies. In my experience it wil be the TL074 on the rear jack board, but we'll see.

All those op amps are 4580 for the dual and TL074 for the quads.

Does the tape in register an output?

Hi again,
sorry about that but I've never had any dealings with the amp before. It just had 'V Tone' written on the front. On closer inspection, it has GMX 212 in small letters on the back panel.
Well looks like the hunt is over! I disconnected the rear jack panel and the rails have risen to +/-15.

Thanks very much for your help Enzo!