A Buddy at work wants me to try and find out what might be wrong with his MTX Thunder 421D.Recently it started blowing fuses while playing at high volumes.He's had this amp for about a year with no problems until now.He checked all his connections and found his power wire to be loose so he tightened it and replaced the fuses and continued on his way.Now over the course of the next few weeks the problem has become more and more frequent.Instead of blowing a fuse maybe once a week now he pretty much blows them daily if hes got it cranked.i took a quick look at the power supply and output fets visually and saw nothing out of the ordinary.Its been a couple months since I last worked on an amp so I've lost some of my knowledge.How do I go about checking the voltages on the output and power supply fets?I've got some notes from a previous repair that lead me to believe that the power supply fets are good.With the black meter lead on ground and the red lead on the center leg of the power supply fets I'm getting 12.75 volts dc.With the same setup on the first leg I'm getting .003 volts dc with the amp powered on and nothing with the amp off.And on the third leg with the same setup I'm getting that same .003 volts. I'm a little iffy on what voltages to expect and how to obtain them from the output fets.
I was thinking that the speaker could be the problem.I haven't got a chance to check it out for him yet.I noticed while I was checking it out that he had the gain and bass boost pretty high and I'm guessing the settings on his radio are probably the same. He might just be trying to get too much out of that single 10.
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