MTX Thunder 280 Inverter Issue ! - diyAudio
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Old 25th January 2013, 09:53 PM   #1
diyAudio Member
Join Date: Jan 2013
Default MTX Thunder 280 Inverter Issue !

I am trying to fix this amp for a friend, so I do not know the history of it.
It had the two resistors that feed the gates of the inverter missing, with two burnt marks. I have replaced the two MOSFETs (IRFZ11 50A 60V) with two NDP710A 42A 100V). I know this is not a direct replacement, but I had these from a previous project. There is a small thermistor that I do not know the resistance of ?
I would greatly appreciate someone measuring their thermistor at 70 Deg for calibration and letting me know how many Ohms it should read. I have checked the two FEP16CT diodes, they are fine.
Does the LM339 send a start pulse for the inverter to start or does the inverter start automatically, once 12 VDC is applied to the amp?

Thank you in advance for any help.

All the very best, Mad Yank !
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Old 29th January 2013, 01:14 AM   #2
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
I'm not sure about this amp but many of the MTX amps have constant power feeding the LM339 and the TL494. Pin 4 of the 494 is used to enable/disable the power supply. If you want to try to disable the protection circuit, find a small PNP transistor that has it's emitter connected to pin 14 of the 494 and its collector connected to pin 4 of the 494. Remove that transistor. This will disable the protection circuit so you must take all precautions listed on the basic repair page to prevent damaging the amp further.

With the protection circuit disabled, does the amp produce clean audio?
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