edit (Tall tell signs to a blown amp) Problem fixed!

SharkyRivethead · « **on:** 5 Jan 2010, 04:40 pm »

After pairing a different sub and amp together, the amp no longer functions. The driver hit one low too low and popped. The sub went dead. I unplugged it and let it be for a while. I was not to concerned about it for my attention was focused elsewhere. Now, I'm back to it and wish to fix it.

I plugged it back in.There is power, but no sound. I matched the original driver to the amp, which was a functional driver. Still no sound. I opened up the sub to look at the board. There is nothing wrong with the board that I can see. None of the caps are blown, none of the resistors are bloated, none of the trace lines are burnt. The amp has a reset switch on the back that is set, there is also a fuse hard wired to the board. It looks like a ceramic fuse of sorts. I was thinking of desoldering it and replacing the fuse to see if it would do anything.

I've never blown an amp in such a way. Is there something I should be looking at first? It's not to say that the driver that was put in could have been one with a lesser ohm rating than the amp could handle. But I very much doubt it. It was just a cheap ass sub.

*Scotty* · « **Reply #1 on:** 5 Jan 2010, 05:09 pm »

I suggest you buy a Digital Multimeter or DMM for short. Use the DC voltage measurement function to check for large amounts of DC voltage being applied to the driver terminals when the amp is turned on. You can also use the Ohms function to test the fuse to see if it is still good.This should be done after the unit has been powered down for awhile to allow the power supply storage caps to discharge. I suspect that the amp is indeed dead but you never know,good luck.
Scotty

SharkyRivethead · « **Reply #2 on:** 5 Jan 2010, 06:55 pm »

I have a small radio shack DMM, not sure if it can read power, but then I should be able to check the fuse. Even though the power and power light comes on, you think the amp may be a lost cause? I was wondering if it would have something to do with the audio line of it. Don't know if that makes sense. Trouble shooting suggests....

1 If in fact the driver had a lower impedance (4ohms) than the amp was rated for. Is there an order in which I should check things? From high/low input terminals, all the way up to the the driver connection.
2 If it was just the speaker being a piece of crap and it blew, what route would I take?

In the past I would have just replaced the speaker. But I truly want to learn how to make/repair my own stuff. I'm trying to find some good books for beginners. But the financial situation has me waiting a bit. If there are any good websites that can be recommended that would be great. Most don't seem to offer much....at least the ones I've come across.

TomS · « **Reply #3 on:** 5 Jan 2010, 06:57 pm »

This is a nice site to get you started, all free http://sound.westhost.com/articles.htm

*Scotty* · « **Reply #4 on:** 5 Jan 2010, 07:33 pm »

With the power on put the DMM into its DC voltage reading position 200 volt setting and put the probes across the drivers terminals and see if there is any DC voltage present. If you don't get any reading at the 200volt setting start downward on the scale until you reach the 200milivolt postion. If power is being applied to the circuit there should be some voltage there. Be sure that you have the amp in its constant on mode and not an auto mode where the amp only turns on if a signal is present at the inputs. It would not be a bad idea to put shorting plugs in the inputs just in case the amp does like being turned on with no cables connecting it to a source in place.Frequently when a major failure occurs the amp will put the entire rail voltage out the door and apply it to the driver,this is why in-line speaker fuses are in place,they blow and save the driver. More advanced protection sometimes uses relays for this function. If the fuse is not blown I really don't have any bright ideas to suggest. If the fuse is blown replacing it may result in further damage to the circuit farther down stream as the fuse blew for a reason.Tracking down step by step what blew and where is beyond the scope of an on-line exchange.
Scotty

SharkyRivethead · « **Reply #5 on:** 23 Feb 2010, 12:22 am »

I am soooo proud of myself! *pats myself on the back*

I fixed my sub. I tracked down the problem to a blown IC. It was a stereo amp IC. After ordering the part and resoldering it to the board....soldering a 15 pin IC was not easy, considering I've never done a IC before. Anyways, reinstalled everything and the sub works perfectly.

The problem was caused by pairing a 4ohm driver with a 6ohm amp.

I'm only posting this for those who helped can see. Thanks everyone, saved me at least 200.00 for having to take it in and getting it repaired.