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JBL MP 418


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#1 BigBrodeur

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Posted 07 August 2006 - 10:21 PM

Hi everybody.

I'm experiencing a recurrent problem JBL's  MP-418 amp.
It seems that, after a while, they are having trouble evacuating the heat.
I tested a brand new unit, out of the box with a pink noise running and peaking
slightly on  4 ohms load, full power ( both sides with low pass on
for hours without problem

The units I get for repair mostly have the same problem;  they cant take
this test for more than 30 minutes before going on thermal fault.

Electronically speaking,  everything look fine.

I found that, reversing the fan  i.e. having it pushing air into the unit instead of
pulling it,  the amp stay on a lot longer.  In fact, as long as the new unit.  But I'm sure there must be a reason why fans are pulling air ... and this is not a final solution.

So I was wondering if any of you out there ever witnesses the same problem;
and, most important, found a solution.

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#2 DGlass

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Posted 08 August 2006 - 07:16 AM

Although Crown manufactures the amplifier in question they are a JBL product and design. As such Technical Support questions should go through JBL Technical Support. smile.gif

#3 Lou

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Posted 14 August 2006 - 08:28 AM

I'd check your darlingtons. They're the two or three square transistors located next to the LV regulators heatsinks. They're probably not all turning on. Sometimes the collectors loosen up from the board. They'll need to be re-soldered. There's also a bulletin that adds a heatsink to these.
And then you could have a bad fan. Good luck.