NHT SW10 Subwoofer no sound

[redoxy]

Unit was working then one day no sound with the unit humming when the power switch is in the off position. When I move the switch to the Auto or ON position, nothing happens, the humming stops but no sign of life (power LED was off). I opened the amplifier and noticed one of the main power 6800uF capacitors was bulging. I replaced both 6800uF capacitors and also replace the large resistors (R41 and R140) since they looked burned. The humming when power switch is in the off position was still present but the unit will power on now. Tried connecting signal to it but then no sound. When I move the power switch from the off position to the Auto or ON position and vice versa, there is a loud pop sound. The pop sound also occurs when I move the phase switch or the Audio/video switch

After reading some subwoofer "no sound" threads, I replaced all the electrolyte capacitors on the signal input board and noticed most of the 22uF 50v capacitors were bad. That did not solve the no-sound issue.
The manufacturer (NHT) is generous enough to make the schematics available.

Hoping some of the experts here will help point me in the right direction.
Attached are some pictures and the schematics. Happy to answer any questions, and take additional pictures or measurements.

Thanks in advance

[redoxy]

Re: NHT SW10 Subwoofer no sound

Any help please.

[eccerr0r]

Re: NHT SW10 Subwoofer no sound

Do check to make sure all switches and connectors are conductive when they are supposed to be conductive and not when they're not. Make sure you actually get full voltage on your power rails. Check to see with your multimeter if there are any transistors whose pins are shorted together, use diode check mode and see if any show less than 0.1v in a junction both ways.

As you probably can see, most people look at pictures and see if there are any obviously blown components. Either there are none or it's not visible. At this point if nobody can spot any obviously damaged components, this is what people get paid big bucks for doing component level debug, unless they are experienced with this specific model.

What tools do you have at your disposal? Things that are helpful are oscilloscope and/or a test amplifier/headphones with limiters so you can probe along the signal path to see where the signal stops...

[redoxy]

Re: NHT SW10 Subwoofer no sound

Thanks, eccerr0r. I appreciate the input.

I will proceed as advised. I can at least rule out all electrolyte capacitors since I have replaced all. Unfortunately, I have basic tools. I do not have access to an oscilloscope or a test amplifier/headphones with limiters.

Keeping fingers crossed it will be one of the transistors when I test them.

Thanks again.