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Class D amp cooking output inductors?
Class D amp cooking output inductors?
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Old 16th July 2017, 08:50 AM   #1
ThyDntWntMusic is offline ThyDntWntMusic  Australia
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Default Class D amp cooking output inductors?

So I was recruited to repair an Option Audio OAX2000 amplifier.

It had killed its power supply mosfets, and somehow ONE of its TO220 package diodes.

I replaced all the mosfets, and all the diodes, and as a result, one bank of mosfets decided to run constantly on.

SO I replaced the 8 drive transistors, and the TL494, and we're all good.

Or so I thought.

After running for half an hour at very low volume, something smelt hot, I soon realised it was the output inductor, sitting at 90 degrees Celsius

I swapped out the paralleled 10uf, 100volt non polarised electrolytic capacitors, for some polyester ones borrow from another amp, but this made no difference...

Ideas? Thanks!

Last edited by ThyDntWntMusic; 16th July 2017 at 09:00 AM.
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Old 16th July 2017, 10:30 AM   #2
Perry Babin is offline Perry Babin  United States
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Photo of board and inductor?
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Old 16th July 2017, 10:38 AM   #3
ThyDntWntMusic is offline ThyDntWntMusic  Australia
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Thanks!
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Old 16th July 2017, 10:41 AM   #4
ThyDntWntMusic is offline ThyDntWntMusic  Australia
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Old 16th July 2017, 10:42 AM   #5
Perry Babin is offline Perry Babin  United States
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Those tend to run hot but 90c is very high. I'd suspect a shorted turn. It's most common where the terminal winding comes over the top of the rest of the windings.

Twist/push/pull the inductor while closely watching the idle current. If the idle current changes when twisting, it's likely shorted.
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Old 16th July 2017, 10:51 AM   #6
ThyDntWntMusic is offline ThyDntWntMusic  Australia
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Poking, prodding, twisting, doesn't seem to make any difference...
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Old 17th July 2017, 02:24 PM   #7
MarioRestucci is offline MarioRestucci  Italy
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I've a USBLASTER USB3003 that use two SINUS LIVE SLA1500 board, internally linked.
I've the same "issue".
At this point, i don't think that is an issue.
The two inductors come hot in 10-15min producing a clear audio output.
despite this, the amp work correctly and not have a high current draw.
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Old 19th July 2017, 08:07 PM   #8
ThyDntWntMusic is offline ThyDntWntMusic  Australia
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How hot are your inductors though? Have you measured the temperature?

Thanks!
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Old 19th July 2017, 08:40 PM   #9
MarioRestucci is offline MarioRestucci  Italy
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I've not a thermometer but if i touch the inductors are very hot...
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