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Newbie needs help with QSC MX700
Newbie needs help with QSC MX700
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Old 18th October 2013, 04:34 AM   #1
bwilliams is offline bwilliams
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Join Date: Dec 2011
Default Newbie needs help with QSC MX700

I have a QSC MX700 that has no output. I am relatively new to diagnosing amplifier problems so if someone has some patience and knowledge, I am willing to do the work. I can identify and test all the components on the board, just not sure how they come together to do what they do so I need some guidance.
Problem-no sound from either channel. I have checked voltage from transformer and have 96VAC on both sides. From the rectifier, I have 132VDC and if I am doing it right, I have no 15VDC coming out of my power supply. My VCC is 132VDC. I checked all the transistors with a diode tester and they all read the same so one could assume they are okay. All my caps read proper on my capacitor checker. Any help? Here is a link to the website that has the manual with a schematic for this unit. Thank you in advance.

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Old 20th October 2013, 06:31 AM   #2
djk is offline djk
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Join Date: Feb 2001
Location: USA
The 15V zeners burn out on these, replace the opamps at the same time.
Candidates for the Darwin Award should not read this author.
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Old 31st October 2013, 10:31 PM   #3
bwilliams is offline bwilliams
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Join Date: Dec 2011
This one turned out to be relatively easy. I followed the circuit along and found there was nothing after the thermal switches on the heat sink. Turned out to be bad solder joints on these and also at the two four pin connectors from the transformer. Went around and resoldered everything and now it works like a charm. One thing about getting older, need a bigger magnifying glass.
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