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The owner of the Peavey XR800D 200 Watt per channel mixer loves it and wants it fixed. I already changed a few sliders on it and apparently he hadnt used it in for a while prior. The problem now is after it runs for a minute or so at high output, say with a 40+ V P-P sine wave riding on both left and right main speaker loads (running with wire wound resistor loads), the fan starts on the power supply and the output drops on both channels down to a few volts P-P, with sine waves still looking OK. I dont have a schematic yet so test points need TBD. Thinking power supply...what in your collective experience do you think is happening? Thanks.
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Is the 48 volt supply rail staying constant? How about the low voltage rails? I can't post the schematic here, it's too big unfortunately. Peavey will email you the schematics though, that's where I got them (I have the XR1200D). Or give me an email address that can handle 3 meg files. -
Here, I used a freebie PDF editor and cut out everything but the power supply board part. Maybe this can get you going.Comment
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Bill, Thanks.I have ordered from Peavey previously. Prob will call for additional pages esp power transistor board.Comment
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Is this the problem with the amp, that it shuts down after playing loud for a time? How hot are the heatsinks getting when it shuts down? When it cools down, does it start to work again?Comment
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Quote:"running with wire wound resistor loads"
What is the resistance of the load that you are driving?
This is the rating of each power amp.
135 watts into 8ohms
240 watts into 4 ohms
130 watts into 2 ohms.Comment
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Yep, I had forgotten that the XR800D was only a nominal 200 wpc, while the 1200D and 1600D were 300 wpc.Comment
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I am running with 8 ohm resistive loads rated at appx 100 watts. They get hot as I push the output to appx 50 v p-p but shortly into the test the fan kicks on the power supply and the output starts dropping.
This is consistent with the complaint that the owner said when he began his set the output started clipping. Though he said he flipped his speakers from left to right and got thru the set, though running left channel low (monitor) and right channel driving hard.
I will rerun the test and monitor the rails. Thanks.Comment
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I don't use Volts P-P.
My scope displays RMS.
So if that 50V P-P is true (RMS= 0.3535 x V P-P) that is a 17.67 Volt output where this happens.
Tha's 39 watts at 8 ohms.
I would hook up a decent volt meter & read the output to verify the output voltage.
The fan kicking in & then the amp output drops is weird.Comment
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This is off the back burner and need to get it fixed... The supply voltages seem to be holding up as the power output drops off. I have not enough experience with Transistorized amps to have previously seen a situation where the power drops off as this does, though using the resistor loads and a sine wave input not sure if there is a distortion component...
If someone can post the power amp portion of the schematic it would help greatly. I believe the mixer section is fine...the headphone output is good. I plan to remove the mixer and drive the power amp directly and scope it. If I knew the expected levels would help in isolation.
Still may need to call peavey if not just to hear the sweet southern accent of the parts lady...Comment
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