JL Audio AMP MHD750.1 Turns on! Power goes from GREEN TO RED - diyAudio
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Old 23rd April 2012, 04:14 PM   #1
diyAudio Member
Join Date: Jul 2011
Default JL Audio AMP MHD750.1 Turns on! Power goes from GREEN TO RED

Hi my name is Joey i have here is a JL AUDIO AMP MHD 750.1 The was working it was pushing one 15 cerin vega now it blew the sub and i installed new subs kicker L7 only to find out that the amp wasn't working. So when i pulled the amp off the amp rack i turn on the key and found that the power led light was going back and forth from GREEN TO RED, was wondering what to check for thank you
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Old 5th May 2012, 03:57 PM   #2
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Join Date: Aug 2008
Hey Joey,

It sounds like the amp is going into a protection mode. When the subwoofer it was driving died, it may have taken part of the amp with it. It may have damaged the output stage.

Unfortunately these types of things are very hard to debug just on the forum with only text. The good news is if the amp is alive enough to power up, figure something is funny, and go into protection mode it can probably be repaired. But you might want to take it to a local repair shop.

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Old 5th May 2012, 11:27 PM   #3
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Join Date: Apr 2008
Location: Carlisle, England
First stop is checking the output transistors.
Could be the class d chip went with them tho.
Murton-Pike Systems PCBCAD51 pcb design software. http://www.murtonpikesystems.co.uk
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Old 6th May 2012, 06:38 AM   #4
MOER is offline MOER  United States
diyAudio Member
Join Date: Aug 2003
Default HD750

There are no output transistors Nigel, they are MOSFETs.

These amplifiers are extremely complex and unless you have a lot of experience with class D amplifiers I suggest you send it to someone who knows these amplifiers. This amplifier employs the single cycle technology which is one of the most complex circuits I have worked on.

The power supply is also complex and they use a separate switcher for the front end whose frequency is clocked to the main PWM chip

Steve Mantz
Zed Audio
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Old 11th July 2012, 07:12 PM   #5
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Join Date: Jul 2011
hi Moer if i send the amp too u can u fix it for me and how much? please i love this amp
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