MTX Audio Amp. Powers up, no sound.. Bad caps??

[Mike Kennedy]

I have a Mtx thunder 6500d amplifier. It powers up, but does not work.. It
has 4 5600uf 63v caps inside it, and the tops of 3 of them seem to be
slightly bulged up.. You can push it down but its like the plastic is warped
and pops back up. Does mean the caps have been overheated and are possibly
bad? Any other ideas on what to check?

Almsot everything else is surface mount components.. : ( so that makes this
thing real fun to work on....

Thanks in advance

-Mike Kennedy

MikeK400 _at_ earthlink.net (replace _at_ with @)

 

[Jfet]

The 4 5600uF 63V caps are most likely in the power supply section. These filter the high
voltage supply required to drive the output transistors. Most caps are designed to vent
when they fail, otherwise, the shrink wrapped shell usually melts and separates. If it
powers up, you need to check if you have high voltage at the transistors.

This requires you to know where the power leaves the power supply. If it had shorted
output transistors, it would more than likely not power up.

However, there are most likely MOSFET transistors in the power supply section. These get
hot, and explode for whatever reason (overdriving the amp, etc etc....)

Your problem could be simple, you just have to diagnose it properly.'

First check the voltages.

If all voltage is good, and visual check of components are ok (test the caps using an ohm
meter, otherwise you can view the output of the DC V with a scope), inject a signal (sine
wave) and follow the signal till it stops. You'll certainly have signal at the RCA
inputs, you may continue to have signal past the several op amps (depending if you have a
cross over, etc.. ), then the pre-drivers, etc..

It is tricky, but can be done.

It is easy when you have the right equipment, but if the caps failed, that means something
else made them fail. That is your job to figure out what happened