One of my circuit boards is blown (104 sub 15000 V06 SCS 150PW) in my JBL sub150 subwoofer. Any chance of a replacement board or an easy fix?

replace C42. easy fix. ordered the new capacitor from amazon (100uf 35v)

Fuses blow when something is shorted. In this case it will be a semi-conductor of some kind. If the device uses IC for the main amplification then you are right to be worried!

The 158 amp is totally unsuitable for the JBL.
This is the specification of the JBL:

• Recommended Amplifier Power 10 Watt
  
• they are also 4 Ohm speakers.
• 158 is: Output Impedance / Channel
  8 Ohm.

Isolate the power transformer from the circuit board, just to determine

if it is from transformer or from circuits on the board.

There is a guy on Ebay who repairs these - not sure but I don't think the board is available - you could check with Harmon - they own Infinity and JBL

Didn't it come with a manual?

Of course it needs external electronics to provide sound sources, controls, bass management AND amplification for the other speakers. It's just a sub.

Have you checked the Impedence of the old speaker. If you can measure to below 8ohms you need not replace the speaker. Check with proper LFe signal at input of your amp. Also check for power indications before going further.

Check that the audio source is feeding the sub is wired correctly and that there is no problem with the leads if you still have no joy and you have a multimeter check that the speaker isn't blown allthough it would be very odd if it was it still rules it out. after this you could be looking at any number of problems IE bad joint on the circuit board blown parts the list is endless try the simple sollutions 1st

The boards can be repaired - look for we repair and your model number on ebay -

poor design, the amps that are screwed to the heat sink are below a transistor which is catching all the heat,heat rises and changes the bias of the transistor so high it causes runway in circuits that results into failure also the amplifiers are sealed with no air flow, this can't be good.Maybe if they put air vents or remove the cover to panel then the heat will have somewhere to go instead of just building up inside.If this problem is not fixed a replacement is going to fail too.good price bad design.

check the cable between your sub and the receiver for short circuit and if the cable is ok you will have an problem in the printed board.