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Old 8th August 2008, 01:34 PM   #1
Tom7227 is offline Tom7227  United States
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Default KRK V88 Over heating problem

Gentlemen,

I am having a problem with a KRK V88 studio monitor that came into my shop for repair, and hoping for some enlightenment.

It uses (2) LMLM3886 in parallel to drive the Low end and another LM3886 to drive the high.

The problem is that as you begin to supply audio to the amp, the LOW bass driver IC's get WAY hot, and eventually distort.

I replaced both IC's with no success, I thought perhaps the power supply caps (12,000uf) were the problem, but no. I also looked for High frequency oscillation...none there.

Any idea guys?

Tom
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Old 8th August 2008, 04:09 PM   #2
Tom7227 is offline Tom7227  United States
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Might someone have a schematic?
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Old 9th August 2008, 01:28 AM   #3
Tom7227 is offline Tom7227  United States
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Default The fix

For those folks who like follow ups,

heres the deal,

Two LM3886 are in parallel to drive two woofers, and another LM3886 drives the midrange/tweeter.

All the IC's were getting warm at idle (no audio), when audio is fed into the monitor, the IC's would get blistering hot, and eventually fail. (but they cool, and they are fine)

The clue was to seperate the two LM3886's that were in parallel, the outputs of each IC joining at a .4 ohm resistor to feed the speaker. Each IC had audio feeding it, but only 1 had an output.

Pin 8 of this IC was called mute, it had an RC network and tied to all the other Pin 8s.

The one that wasn't working had a leaky .1uf cap. Small little blue thing.

Worked all day on this thing...made no profit...BUT..I share this with all of you.
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Old 9th August 2008, 01:49 AM   #4
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Thanks tom,for sharing it with us.We never stop learning!
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