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I need a schematic for the switcher power supply on this. Anyone got one?
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Does the circuit board say Alesis on it? I don't know the unit, but many OEMs buy switchers from another vendor.
I have repaired many switchers over the years, what is wrong with yours? I check the rectifiers for shorts, the chokes from coming loose, the switching xstrs for shorts, e-caps for dryouts. Just a few things to do without documents.Education is what you're left with after you have forgotten what you have learned. -
Yep - says Alesis on it.
Recitifers were my first guess...they all seem to test in the 0.3-0.4 range
Only ONE of the voltage rails seems to be having difficulty - and I want to trace where the voltage rail goes - with the board populated it is a !^$%@#& trying to see the traces.
With the Behringer switcher, they used a well known example circuit from a switcher manufacturer - It was easy to trace. With this one I can't even figure where they're doing the regulation...Comment
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Who says they are? Many switchers regulate the 5v for the computer parts, and the analog voltages just follow along. The draw on these supllies doesn't vary much anyway.
What problerm with what voltage? Is the PS bad or is it loaded down by the loads?Education is what you're left with after you have forgotten what you have learned.Comment
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Ah I just ASSUMED that they would regulate. They're really are no computer parts on this - so there is NO regulation - you got it! I was looking for something that didn't exsist.
Both under load and without load, the -36V rail is all over the place - and there is a ticking noise, like something is arcing. Just the -36V rail, nothing else. All the other voltages are fine...Hmm...
I just can't see the traces well enough to figure out where the voltage is coming from, if you get my drift.
Thanks! I';ll probably take another stab at it...Comment
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Look at the foil side of the board. For safety certification, the high voltage stuff needs to be isolated from the low voltage side. So generally there is a space running across the board where the HV tracery is separated from the LV tracery. If the thing works otherwise, chances are the HV side is OK. At least we hope. SO you can see the parts that make the LV. Mysterious gaps in teh traces are probably bridged by inductors.
The transformer will have secondaries just like a linear supply. Pairs of rectifiers, or possible dual rectifiers in a TO220 or similar package mounted to a heat sink will rectify the stuff that comes out. Not remotely a sine wave, very square wave. The rectifier will see a first filter, then a coil, usually toroidal, and often shared by several windings, followed by a second filter.
Is the PS loaded? Don't know about this one, but some switchers don't work right without a load. They will cycle startup and shutdown. And that can make a ticking sound.
What does a scope say on the outputs?
By the way, the primary side of the switcher is direct rectifies AC mains, and usually voltage doubled, so there is like 300VDC at all the current the wall can provide. DO NOT connect a scope to anything there unless the PS is running off an iso. The secondary side is OK, as it is isolated already and referenced to ground.Education is what you're left with after you have forgotten what you have learned.Comment
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Nice one, I have an one on the bench and was just about to give up on it, until I read this and checked over the circuit board again and found there was a broken track from one of the mains filter caps to a power resistor. Turned an ok day into a good day!Comment
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