Peavey PV14 mixer, 2012

Surprisingly strong "electrical" smell around the vent ports. Blown TOP244YN , 20 ohms across rectified mains cap. Considering crack to its encapsulation is just observable, on one side only and then under x30. Distorted top to the sillypad (TM) , what may be a puncture hole at the non-rounded, but then not sharp, rear upper edge. Hang on a bit , although the tab holding bolt has an insulating washer, the heatsink is isolated, anti-EMI ?. So if it did puncture , why leading to failure? Any known problems with these presumably fairly generic SMPS sub-units, all else checks out (cold) ok. Mica will be going back in there.

I had a similar mixer in a while back, and it too had a blown TOP chip, but not cracked like yours. To save a bit of troubleshooting time I phoned Peavey UK service dept to see if there were any knows issues regarding the PSU, and was there something that might have broken the TOP chip, or was it just the TOP chip that broke. I was told (a bit sheepishly) that they knew about these TOP chips blowing up, and if I replaced it the mixer should be fine.

I did, and it was.

Cheers,

Gareth.

Are these "chinese versions" of TOP244YN or the real McKoy? I bought mine from Farnell.

Gareth.

All I know is the back face is flat unlike the curved one I came across in a blown Yamaha Stagepas recently, TOP249YN , one of two push-pull , pirate or just sloppy manufacture, maybe stress relieving of the metal after guillotining/machining, developing over time.

Anyway this time. The drummer knocked the mains lead. I wonder if there is an Achilles heel with such 110/240V mains voltage auto-sensing SMPS drivers, if there is a short duration interupt in power and then auto restart after the 8 cycles noted in the datasheet of these TOP24*YN devices. Did you get any insight in to what preceeded the failure of your unit?

Surprisingly strong "electrical" smell around the vent ports. Blown TOP244YN , 20 ohms across rectified mains cap. Considering crack to its encapsulation is just observable, on one side only and then under x30. Distorted top to the sillypad (TM) , what may be a puncture hole at the non-rounded, but then not sharp, rear upper edge. Hang on a bit , although the tab holding bolt has an insulating washer, the heatsink is isolated, anti-EMI ?. So if it did puncture , why leading to failure? Any known problems with these presumably fairly generic SMPS sub-units, all else checks out (cold) ok. Mica will be going back in there.

Oops, I just remembered, my TOP chip wasn't "blown" as such, it was overheating and shutting down. I rang Peavey to try and quickly establish if they knew of anything that might be overloading the chip, or was it just the chip.

Gareth.

Reason for the tab insulator. 20mm high heatsink 2 mm from the metal chassis, so only arctan(2/20) = 6 degree, bending of the pcb would let

340V touch ground.

Going by the curved over top of the sillypad, this has been subjected to substantial heat. This is not a mixer-amp, just mixer loads of apamps and a big DSP chip, so why the heat? Vents are either side of the chassis with no venting local to the smps which is hemmed in between chassis base and main pcb

Decided to grind 4 holes through the pcb in the heatsink footprint and give a graduated set to the vanes, to make a staircase, either side, pointing away from the IEC, plus mica insulator for the replacement. Perhaps the set to one side plus air from under the pcb may give some sideways movement. Despite not the slightest local discolour indication of the pcb overheating or any of that telltale dust accumulation on the underside of the main pcb directly over the heatsink. But I feel I have to do something other than just direct TOP replacement

Decided to grind 4 holes through the pcb in the heatsink footprint and give a graduated set to the vanes, to make a staircase, either side, pointing away from the IEC, plus mica insulator for the replacement. Perhaps the set to one side plus air from under the pcb may give some sideways movement. Despite not the slightest local discolour indication of the pcb overheating or any of that telltale dust accumulation on the underside of the main pcb directly over the heatsink. But I feel I have to do something other than just direct TOP replacement

The replacement chip I fitted did not overheat. Perhaps there is a batch of dodgy chips out there that have a failure mode that causes overheating.

Unlikely as that sounds, it fits in with my experience, and the fact that Peavey seem to know that these chips "break".

Why not just fit the new chip and see how hot it gets? You shouldn't need to add any extra cooling.

Gareth.

Putting my deer-stalker hat on. Someone had been inside to replace the fuse. Left out some of the screws, including one self-tap that holds the IEC. If that one was previously missing and the IEC just "held" by the remaining one next to the TOP heatsink,loosened by repeated IEC insertions AND the sillypad was punctured or close to puncturing. Then the drummer tripped over the lead, IEC twisted and the IEC holding screw touched the heatsink, as it is long enough, then blown TOP244, but about

4mm gap to swing across to do so. But as there are no pcb standoffs to chassis in that area, relying on the IEC screws to chassis, then perhaps the whole pcb being tilted in a downwards sense, by drummer standing on the lead, and then only that arctan(2/20) 2mm gap for heatsink to contact chassis.

This could be your over-temp drop-out failure mechanism. Sitting quiescent for 1/2 hour and an IR thermometer to the TOP body 38 deg C. But if you point it to the rear it picks up 78 deg C of the 330R dropper that is enclosed on all sides by the ps pcb , heatsink,chassis and main board. Perhaps over hours and lack of through draft that radiator heats up the heatsink and so TOP , enough to trigger temp protect. Hopefully the holes I ground through the ps pcb and the staircasing of the h/s vanes will preclude that.

This could be your over-temp drop-out failure mechanism. Sitting quiescent for 1/2 hour and an IR thermometer to the TOP body 38 deg C. But if you point it to the rear it picks up 78 deg C of the 330R dropper that is enclosed on all sides by the ps pcb , heatsink,chassis and main board. Perhaps over hours and lack of through draft that radiator heats up the heatsink and so TOP , enough to trigger temp protect. Hopefully the holes I ground through the ps pcb and the staircasing of the h/s vanes will preclude that.

My TOP chip was obviously overheating, you could tell immediately by putting a finger on it. It would shut down in 10 to 15 minutes.

The new chip went back in the same place on the same heatsink at the same angle. This one did not get finger hot.

Gareth.

This could be your over-temp drop-out failure mechanism. Sitting quiescent for 1/2 hour and an IR thermometer to the TOP body 38 deg C. But if you point it to the rear it picks up 78 deg C of the 330R dropper that is enclosed on all sides by the ps pcb , heatsink,chassis and main board. Perhaps over hours and lack of through draft that radiator heats up the heatsink and so TOP , enough to trigger temp protect. Hopefully the holes I ground through the ps pcb and the staircasing of the h/s vanes will preclude that.

My TOP chip was obviously overheating, you could tell immediately by putting a finger on it. It would shut down in 10 to 15 minutes.

The new chip went back in the same place on the same heatsink at the same angle. This one did not get finger hot.

Gareth.

Just to clarify, these symptoms were observed with the unit dismantled and the PSU in free air, so I could put my finger on the chip/heatsink.

Gareth.