Peavey XR684 no sound

jvm · 10-11-2009, 09:26 PM

I have a Peavey XR684 and aXR684+ with the same problem in both units. No signal to power amp. Preamp outputs are working. No sound when plugging into power amp in jacks. Anyone aware of a common failure with these preamps?

Enzo · 10-12-2009, 03:23 AM

Well, so far one thing they may have in common is the same speaker and speaker cord. Did you try others? And for that matter, if bith were used with the same gear, it is possible a problem with a speaker or cord caused the power amps in these to fail.

Beyond that, look inside. ANy blown fuses in there?

Is there ANY sound coming from the speakers? Even a little background hum or something? Or is it utterly silent?

You say "No signal to power amp." If you mean that literally, then explore the ribbon cable from the mixer portion to the power amp. Is one end coming free? If there is signal at the main outs on the front panel, there is still a couple stages between those jacks and the actual powr amp board - could be a failure there, so scope the actual last stages on the front board.

However if what you really mean is that there is no signal FROM the power amp - ie to the speakers - then we are assuming the signal gets to the power amp's own input OK. In that case, verify the high voltages are about 60v. And also verify that the ICs on the power amp board are indeed getting their +/-15VDC power supply.

It would seem significant that both channels of these dual powr amps are silent. Is that correct? The only thing they share is power supply, cabling, and the PV mute circuit - signal "X" on the schematic. The mute circuit is only a couple transistors, so easy to check or disable, but the odds of both amps having a mute failure seem remote to me.

As far as I know, the XR684 amps used the 400SC power amp board. Is that what is in your amps? There were at least four versions of the 400SC - 1998, 1999, 2001, 2005. Which one do you have? Or if none of them, what do you have?

jvm · 10-12-2009, 03:40 PM

Thanks for the suggestions, Enzo. I can inject a signal at the ribbon cable and have sound, so I know the power amps are ok. I will take a look at the final stages on the front board and see what is happening there.

10-11-2009, 09:26 PM	#1
jvm Junior Member Join Date: Jul 2009 Posts: 8	Peavey XR684 no sound I have a Peavey XR684 and aXR684+ with the same problem in both units. No signal to power amp. Preamp outputs are working. No sound when plugging into power amp in jacks. Anyone aware of a common failure with these preamps?

10-12-2009, 03:23 AM	#2
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 9,266	Well, so far one thing they may have in common is the same speaker and speaker cord. Did you try others? And for that matter, if bith were used with the same gear, it is possible a problem with a speaker or cord caused the power amps in these to fail. Beyond that, look inside. ANy blown fuses in there? Is there ANY sound coming from the speakers? Even a little background hum or something? Or is it utterly silent? You say "No signal to power amp." If you mean that literally, then explore the ribbon cable from the mixer portion to the power amp. Is one end coming free? If there is signal at the main outs on the front panel, there is still a couple stages between those jacks and the actual powr amp board - could be a failure there, so scope the actual last stages on the front board. However if what you really mean is that there is no signal FROM the power amp - ie to the speakers - then we are assuming the signal gets to the power amp's own input OK. In that case, verify the high voltages are about 60v. And also verify that the ICs on the power amp board are indeed getting their +/-15VDC power supply. It would seem significant that both channels of these dual powr amps are silent. Is that correct? The only thing they share is power supply, cabling, and the PV mute circuit - signal "X" on the schematic. The mute circuit is only a couple transistors, so easy to check or disable, but the odds of both amps having a mute failure seem remote to me. As far as I know, the XR684 amps used the 400SC power amp board. Is that what is in your amps? There were at least four versions of the 400SC - 1998, 1999, 2001, 2005. Which one do you have? Or if none of them, what do you have? __________________ Education is what you're left with after you have forgotten what you have learned.

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10-12-2009, 03:40 PM	#3
jvm Junior Member Join Date: Jul 2009 Posts: 8	Thanks for the suggestions, Enzo. I can inject a signal at the ribbon cable and have sound, so I know the power amps are ok. I will take a look at the final stages on the front board and see what is happening there.

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