Energy AS-90 Subwoofer Issue

[molalani]

I decided to replace all the electrolytic capacitors in this old home theater sub as it was starting to act "funny". When a standing fan was turned off, on the same circuit, it would send out a thump. Also, when I turned the power off, it would also make a loud noise. In addition, when connected to no input signal, the sub woofer would be vibrating erratically. I have another sub that did not relay the ground noise from the fan. I also tried it in another home and it exhibited all the same issues therefore I didn't think it was a grounding issue with the home circuit so I figured maybe a cap was on its way out. None of them were looking expanded, but I figured for about $10 it would be a cheap attempt at a fix.

In the process, I made a colossal mistake and reversed the polarity on one of the two largest capacitors in the circuit , specifically a 4700uF, CF9 (see schematic attached)

I then powered it up and the fuse blew instantly.

I looked over the board and realized my idiotic mistake pretty quickly, but the damage had been done. I replaced the capacitor once more, but now when I turn on the sub, after the 5 second turn on delay (see attached manual) the sub lets out a large thump and then does not function, however when I turn off the sub, it does let out the same thump it always did.

I understand that a large amount of current would have probably made it through the circuit before the fuse blew, but I'm not sure what I could have blown. My experience with electronic theory is limited, however I'm hoping someone here would be able to help me understand what could have blown or if the symptom that my sub exhibits is a tell tale sign of any specific issue.

Any help would be HUGELY appreciated!

Thanks so much!

Mo

[tahwos]

Re: Energy AS-90 Subwoofer Issue

If you are still working on this - those boards have really crappy through-hole plating, and you may have inadvertently "disconnected", one side of the board, from the other.

i.e. One of your caps may not be soldered, to the top of the board, completing the circuit, because the hole plating came out, with the old cap or is just broken..

[Longbow]

Re: Energy AS-90 Subwoofer Issue

I'm not sure your backwards capacitor actually wrecked anything. The loose eyelet theory sounds reasonable, so make sure the cap is soldered on top and on the bottom of the pcb. There are 2 ways to go here if you approach it without much experience. Basic multimeter voltage checks will probably find the problem, but you have to make note of where and how much voltage you measure. Or you can throw darts at the schematic to figure out what part to replace next. As with anything, you need to start with the power supply. The +/- 15 volts power all the op amps. The +/- RAIL (probably about 35 volts) powers the audio output. I always love subwoofs with the amp inside the cabinet. The electronics are subjected to high heat and constant vibration. Any history on this unit?

[teg93gsr]

Re: Energy AS-90 Subwoofer Issue

molalani, Did you fix your problem. I too have a problem with my AS-90. Mine would have no sound but if I switched the phase switch to 180 the speaker would vibrate erratically. I purchased a new subwoofer but it would be a shame to throw out the AS-90.

[orrforpm]

Re: Energy AS-90 Subwoofer Issue

Thanks to the suggestions posted I fixed my AS-90. Started with the 4700 uf caps and just as posted I pulled the trough hole plating out. Didn't realize until until new caps were in and unit didn't fire up. Luckily there is another spot for caps because the board is set up for 4. Jumpers through the board solved the problem. Fired up again and had the same buzz/hum as before. Checked the cap pairs further down the chain 10uf pair and 47uf pair and one of the 47's checked bad. Replaced all 4 fired it up and success! Had replaced both the 100k pots a few years back due to bad noise and I notice now they are getting a little touchy. I have had this sub since 1995 and it's the best of all 3 sub's I own, was not looking forward to scrapping it. Was happy to find a schematic here. Thanks again!