I have a infinity interlude il120s and it won't power up. I changed the fuse and it made a quick static noise then nothing. Did that a couple times. Then I opened the back panal and didn't see nothing unusual. I should note about six months ago it was smelling like smoke or something. After that it was fine.

Hi and welcome to FixYa,

Initially, the description "...smelling like smoke..." as it would indicate that indeed something did burned.

Offhand, replacing the 4A fuse restored power temporarily and either burned itself again or allowed further damage to the sub woofer. As you have done, repairs involve opening the unit for a look and see.

Options then are:

• consider a DIY (do-it-yourself) repair if and only if very familiar with electronic components & circuitry, use of a DVM/VOM, a soldering iron/station and safe working practices with electrically powered devices. Access to a Service Manual or at the very least, a schematic diagram would be a necessity;
• should you be uncomfortable with a DIY, perhaps your best bet would then be to seek the services of an authorized Service Center (specially if still under some form of extended warranty) or a qualified professional.

• the power supply used in this model is a switch mode type;
• the sub's amp is a 500W class A-B;
• remove the power supply unit (PSU) PCB (printed circuit board) from main chassis by squeezing the heads of the plastic standoffs with a long-nose pliers;
  
• bench test the PSU;
• tests components Q501, Q502, both are IRF740 MOSFETS;
• tests components R506, R503, both are 22 ohms 0.6 watts;
  
• tests components R505, R502, both are 422 ohms 1/4 watts.

I have a infinity interlude 50 the toggle switysre real sensitive. Might be shorting out. Subwoofer comes and goes. Infinity or harman do not carry these types of toggles anymore do you know if those are replaceable or could o bypass that toggle. It is for the low pass. Thank you