[digitalmind]

Quote:

Originally Posted by bperboy /img/forum/go_quote.gif Unless KLH sends me a schematic, I think I might be better off waiting until i'm in EE in college and can figure out how to reverse engineer the circuit. I'll keep it as a summer project.

Rebuilding this board will not only cost you a lot (!) of time, but the cost of it will most likely be just as high if not higher than buying the same subwoofer again. It's a fun project, and definitely something that's good to lean, but I think designing/building a headphone or speaker amplifier would be much more useful considering the cost that goes into such a project.

You can always buy a cheap speaker amp like AudioCats mentioned, and make a small passive adjustable 2nd or 3rd order filter in the line stage. This isn't hard to do, fairly cheap, and also gives you a good idea of what your first year of EE will be like.

However, a filter like that will cost roughly $20-30 USD if you want it cased, etc. Combined with a cheap amp, and you're already looking at roughly the price of a new sub. Doesn't mean that you shouldn't do it though.

 

[bperboy]

Quote:

Originally Posted by digitalmind /img/forum/go_quote.gif Rebuilding this board will not only cost you a lot (!) of time, but the cost of it will most likely be just as high if not higher than buying the same subwoofer again. It's a fun project, and definitely something that's good to lean, but I think designing/building a headphone or speaker amplifier would be much more useful considering the cost that goes into such a project.

Thats good advice, and I think I might follow it. I'll stick all the parts in my basement and forget about it, but maybe in a couple of years, I'll have a fun project to work on, if only to enjoy the experience of repairing something.

 

[kenleekenlee]

You know, that board really doesn't look too bad. It's burned, yes, but the traces look fine on the back, and all of that brown/yellow/burned crap on the power cap is probably just glue they used to hold it down. If you look on the other board, there is similar stuff around all of the caps. Replacing components is (relatively) cheap and fairly easy with this type of board (thru-hole). This project shouldn't take more than a weekend to finish.

Just _carefully_ discharge the large capacitors (with an appropriate resistor, not a screwdriver!) and unscrew the board from the brackets. From the looks of things, this was probably hit with a power spike. I doubt there was water damage - the rust colored crap on the back looks like burned flux. That wouldn't surprise me if there was still tons of flux on the board, judging by the build quality. Several resistors look burned (close to Q9, can't read the screenprint), as well as the two silver-colored zener diodes.

So yeah, take the board off, clean it a little with some acetone, and post some more pictures if you'd like.

Good Luck!

 

[kevin gilmore]

If you think that is bad you should see the power board on heavily
used dynaco stereo 400. Much worse.

The diodes are definitely zener diodes, and they run hot, and after
a while the circuit board definitely will look like that or worse. The
electrolytic definitely needs replacement.

Likely there are other problems preventing the thing from working.
Not the zeners or the cap.

Boy is that cheaply made crap. Better check the driver with an
ohmmeter, or look for fuses. Other than that, prepare to spend
way more time than it is worth fixing it.

You can certainly use an outboard amp, but you are also going to
need a crossover.

 

[threepointone]

That capacitor looks really suspicious. I recall one of the cheapie chinese/taiwanese cap manufacturers which made caps labeled "vent": in my experience a lot of electronics fail because the manufacturers use cheap power supply caps. The top "vent" cap looks a bit deformed, and I think it might have leaked electrolyte from the bottom.

However, I've only seen digital circuits completely fail due only to the decoupling caps--the ripple goes way up and the ICs no longer work reliably / at all. There might be other problems on the board, possibly caused by the ripple or maybe not.

 

[AudioCats]

I thought "vent" means the cap is vented (the top will open to release pressure so it won't explode into pieces)

 

[threepointone]

I mean, what cap manufacturer would be crappy enough that they'd need to advertise that they actually HAVE a vent?

Either way, most of the cheap caps I've seen vent out from the bottom or explode despite the fact that there's a "vent" on the top.

 

[daveg.01]

Guys... I have this same sub. The resistor on the top right (gray) is burnt. It says it’s R63 on the board. Does anyone know what the spec's are on this resistor? It looks like it’s pretty easy to change out.

Quote:

Originally Posted by bperboy /img/forum/go_quote.gif Pics First is the board that appears to be fine. This is the biggest view of the burnt board I could get. The transfrmr is in the way. Closeup of the most burnt part

 

[Nemo de Monet]

You have to love a manufacturer that sticks el-cheapo capacitors rated to 85 degrees right next to power resistors that get hot enough to discolor the el-cheapo PCB. It's like planned obsolesence, only... cheaper.

 

[Alpha 1 Omega]

just in case nobody suggested it LINK

 

[gore.rubicon]

Quote:

Originally Posted by Alpha 1 Omega /img/forum/go_quote.gif just in case nobody suggested it LINK

x2

was just about to say, why hadn't any one brought this one up yet

 

[iriverdude]

Considering the quality of KLH is it even worth bothering with repairing? It's one thing if you were given a M&K S-5000THX.

 

[Shike]

Quote:

Originally Posted by iriverdude /img/forum/go_quote.gif Considering the quality of KLH is it even worth bothering with repairing? It's one thing if you were given a M&K S-5000THX.

I have to agree with this.

At this point a more constructive use of time would be building a sub and throwing this one out . . .

 

[Listen2this1]

Good price good guy

ApexJr Subwoofer Amps

 

[daveg.01]

well.. its junk like it is. I figured it it was an easy fix (just swapping the resistor) it was worth it. It wouldnt take me 5 min to swap it..... just dont know how to tell what part it is.