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Old 9th September 2013, 02:25 PM   #1
rsm5817 is offline rsm5817  United States
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Default Peavey PR12D Loses Power

Any advice is much appreciated - I have a pair of PR12D's (this was an eBay floor unit sold as-is, but said to be "new".) One of them lost power after about an hour of use.

I opened the shell and disconnected/reconnected all of the wires and plugs inside. It worked again for about a week, but the first time I used at live volume, it lost power almost immediately.

If I shake the power module, I can sometimes get a flash of light on the power LED. For the life of me I cannot find a bad connection or solder joint.

Any direction would be helpful. Thanks.
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Old 9th September 2013, 08:24 PM   #2
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You can get the schematic from Peavey.com, the service part of the website. The website also has a forum.
Solder long wires to the main power capacitors, whether switcher or transformer power supply. Run outside the case, terminate so they won't short out. Connect a DVM to them two at a time, preferably meter negative to the analog ground. Use clip leads for this. Play a set. Watch the voltage at the beginning, and then later when the problem is happening. Voltage sags ( pretty common for old equipment) you've found the location of the problem. Hint: the electrolytic capacitors, especially the main ones, if over 15 years old are often the first part to fail.
If not that, you'll have to load it up on the bench with resistors or something, exercise with a radio or waveform generator, and look for something that gets hot when the problem occurs. Takes a meter reading the output at all times, you don't want to blow your ears doing this by loading it with a speaker. I use 5 ohm 200 watt resistors, paired up to 10 ohms if the normal speaker is 8 ohms. You can't use a dual slope integration DVM to read music, they typcially don't read music frequencies accurately and also average the reading over 2 to 4 seconds. You'll need an analog VOM with a 20 VAC scale, or a VTVM, or a scope. If nothing gets hot, you'll have to use the 2 VAC scale and find out where the music goes into always and doesn't come out of sometimes. Block the input probe of a VOM or VTVM with a .047 uf capacitor to prevent it showing AC results on a DC input. My Simpson VTVM has the capacitor built into the probe on the "RF" switch position.
It is not always capacitors. My PV-1.3k PA amp had been putting out 160 VDC on the B channel speaker so often since 1997 the last repairman disconnected the power supply wires to B channel, and put big labels in it "DO NOT USE B CHANNEL!" What is was, was a bad solder joint on an op amp socket, from the factory, in 97. The slightest vibration and the op amp would whang to negative rail and drive the output transistors with them to the positive rail.
It is not always the caps,
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Last edited by indianajo; 9th September 2013 at 08:34 PM.
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Old 9th September 2013, 09:11 PM   #3
rsm5817 is offline rsm5817  United States
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Thanks for the very detailed troubleshooting approach. I really appreciate it.

I will look for the schematic on the Peavey site - I took a look earlier but found only the user manual.

I'm thinking this has to be a simple fault in the power supply circuit. Since last failure all I can get is a brief flash (sometimes) of power.
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Old 9th September 2013, 09:33 PM   #4
dangus is offline dangus  Canada
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I wonder if you can just send the amp module to Peavey for them to repair or exchange? Since it's a current product, Peavey ought to show some interest and concern.
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Old 9th September 2013, 10:46 PM   #5
Enzo is offline Enzo  United States
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You also ought to contact customer service at Peavey to determine if it has a warranty or not. Just because it was sold as is doesn't mean you automatically have no warranty. Most demo units still have full warranty.

The schematics are not so often on their web site, but customer service will always send them. Ask for schematics when you call.

You can send just the electronics to them, but that only makes sense if ALL the wiring is on the module.

I have to doubt it is caps. Even if the caps are totally dried out, the amp would still power up and make noise. It sounds like you are losing all power.

SO try a different power cord. Those go bad as much as anything else does, never assume.

My first suspect is the mains wiring. You have a power cord socket, look at the solder on it, then from there, the mains current flows through fuses. fuse holders. power switches, maybe an inrush limiter, whatever, until it gets to the circuitry. Use an AC voltmeter to see if power is getting that far. The switch and cord socket are on a small board, then a pair of wires goes over to the power supply. Is there 120v on those two wires?

The power supply itself is a switching power supply or SMPS. It rectifies the mains directly and is EXTREMELY DANGEROUS to work on. If you don;t know what you are doing, stay away from it.

Use a wooden chopstick as an insulated probe, and poke at the parts involved. Just because you can'r see a failed solder joint doesn't mean there isn't one. Your mains fuse is on the power supply board, and right next to the bridge rectifier is the inrush limiter, R19. Poke it, he is my suspect.
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Old 10th September 2013, 06:23 PM   #6
rsm5817 is offline rsm5817  United States
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Enzo, thanks so much. I will definitely give this a try and I'll be careful. I did trace voltage form the mains board onto the circuit board and to the fuse holder with full voltage getting to there. I'll check R19 when I get home tonight. I've pecked and poked most everything I could see, but I will take a good look at the inrush limiter for sure.
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Old 23rd September 2013, 01:35 PM   #7
rsm5817 is offline rsm5817  United States
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Update: it seemed that the Quasi-resonant power switch would bring this thing back to life more often than any other component I poked. I replaced it with one from Mouser (same part number). I've got power again - but now the 12D limit light and LED on the front remain red with no signal output.

The manual says it is in protection mode. Any thoughts on this brand new problem? Did I cause this in the resolder? Perhaps I got the new chip too hot - however I did use a heat sink between the chip and solder joints and worked quickly - I tried not to keep heat on the trace any longer than necessary.
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Old 23rd September 2013, 01:37 PM   #8
rsm5817 is offline rsm5817  United States
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Quote:
Originally Posted by dangus View Post
I wonder if you can just send the amp module to Peavey for them to repair or exchange? Since it's a current product, Peavey ought to show some interest and concern.
I sure can. I've talked to their tech support folks in Meridian MS a couple times, very courteous and helpful in troubleshooting. However, I've had no luck yet.
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Old 10th October 2013, 09:48 PM   #9
rsm5817 is offline rsm5817  United States
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Case closed, Peavey was super to deal with. They helped me troubleshoot this and provided some of the best customer support I've ever had. In the end, I sent it for repair. They replaced U3 and some diodes and resistors in the power circuit. If anyone needs the details, let me know.

Thanks to those who offered advice and helped me out. Big time kudos to Peavey!
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