R12 blown resistor replacement

[hotsho111]

Hey, I have a set of promedia 4.1's that were working fine one day, went to work the next day, came home and it wouldn't power on. I took apart the sub and it looks like the r12 fuse blew. I have 2 quesions, if I replace this should it be ok? I've included some pics and the board is a bit burnt. Also, where can I find a replacement resistor?

I also took a look at the r26 resistor and it's not looking so good so I figured I'd replace it at the same time. Where can I find one of those?

Should I replace the main fuse as well (it looks ok though)?

Thanks

Jeremy

[erik2A3]

Jeremy

Nice closeup work on those pictures. A brief thought on your situation with this component: Damage such as this often suggests the presence of some other problem. It's not unlike discovering water- damaged and stained acoustic tiling in a ceiling, and then trying to fix the problem by just replacing the tile with a new one -- when the real problem is a leak in the roof; the newly installed tile will be fine until the next downpour. Speaking of which, was there any chance you had a lightening and thunder storm in your area on the day you discovered this? It's mildly possible the cause were the parts themselves. I don't know what power supply components are associated with this, but it would be far better to send the unit out for a professional evaluation and repair. There may be a very real shock hazard present. It appears that there is a filter capacitor in one of the pictures, and those can hold dangerous charges for days. Moreover, that big cap may be included in the damage report too. BTW: I recently repaired an amplifier with a very visually similar problem, which resulted from a short circuit elswhere that found it's way back to the power supply, taking out several capacitors amd resistors in the process. Good luck, erik

[JJkizak]

If you replace this will it be OK? Probably not. Some parts can be obtained from MCM electronics .com. You should have a schematic diagram to see what circuit those resisters are part of and replace other involved components which could add up to nightmares. But then again you could get lucky.

JJK

[Marvel]

Hey, I have a set of promedia 4.1's that were working fine one day, went to work the next day, came home and it wouldn't power on. I took apart the sub and it looks like the r12 fuse blew. I have 2 quesions, if I replace this should it be ok? I've included some pics and the board is a bit burnt. Also, where can I find a replacement resistor?

I also took a look at the r26 resistor and it's not looking so good so I figured I'd replace it at the same time. Where can I find one of those?

Should I replace the main fuse as well (it looks ok though)?

Thanks

Jeremy

Jeremy,

I'm suprised Erik didn't point this out, but R12 isn't a fuse but is also a resistor, hence the 'R' in the designation. It may be, without replacing, that the solder connection on the burned section of the board is all that is bad. Heating and cooling through some components/solder connections, can cause the solder to deteriorate.

If you can read the values on the resistors, you could go ahead and replace them. Just make sure you match the wattage ratings.

Bruce

[erik2A3]

You'll notice, Bruce, I didn't refer to any specific part -- fuse or resistor, although I did mention the large capacitor. The point, again, is that problems like this (regardless of part involved -- L,C, or R) can be symptomatic of problems elsewhere. Good luck Jeremy, and if replacing a couple of resistors is all this takes, wonderful. Are you able to solder, and are there any static precautions that need to observed with this component? There are some things that could be important to consider prior to doing ANYTHING, and it surprises me that others are not mentioning that. There is not even the slightest doubt that those resistors in question should be replaced, and possibly the capacitor, as well (the circuit board will have to be removed to do that correctly, BTW.) Looking at the pictures again, it seems there may be an MOV present in the PSU, which would of course offer protection against heavy line transients.

[erik2A3]

and an FYI: To read the values on the resistors on the board in this case requires knowing the color coding of the bands. There is information available through the usual searches for that. Measuring with a multi-meter may or may not be suitable because of potential -- probable internal damage. and BTW, there is another part that should be considered, too. There is a single nearby diode, which appears to possibly be a zener, that also shows signs of extreme heating. That should be checked, as well. The whole unit should be inspected for safe operation, particularly if left, as seems to be the case above, unattended. How can one be too careful with this sort of thing?

edit: if you check the image that shows the fuse, there is a light-colored, disk-shaped component just behind it that looks similar to a ceramic capacitor. My thought that it is an MOV (as mentioned above) has been confirmed by its part number. My opinion is that simply replacing burned and damaged parts without trying to determine the cause compromises safety of self and possibly others. I would get it checked out, Jeremy. Erik

[JL Sargent]

Look carefully at the nearest solder joint on R12! Compare it to the other solder joints in all pictures. Looks less than conductive.

Take a meter and test the resistors in question. Judging by how hot that board got, it could be as simple as it looks. That being a cooked component. Anyway resistors do fail, it's just not as common as some of the other components. But hey, they're cheap and you're already in the thing. Swap it/em out and see whats up!

If it were mine, after assurance that no voltage present. I would simply snip the lead of R12 just above the cold looking solder joint. I would then measure resistance across R12 only. I would then measure resistance through that bad looking joint only. After doing these two thing I would expect to know something about R12.

[hotsho111]

Thanks for the replies everyone. They were going into my spam folder
which is why I didn't get back earlier This unit is almost 12 years
old now and hasn't really had any issues besides this (it didn't seem to enjoy the cross country move too much). The one resistor is 47k
and the other is 680, neither are that hard to find (local radioshack
has them). I don't think there was a power issue that night since nothing else seemed to have problems (no clocks had been reset, etc).

Soldering/circuit board work I've done before so I'm not too concerned with that. I was planning on trying to replace them this weekend.

Also, I'm almost positive that resistor should be brown...

I did a quick once over of the board and nothing else looked too out of the ordinary but I'll take a good look at it when I get a chance to see if anything else is damaged.

[erik2A3]

Jeremy:

FWIW: the brown resistor is in bad shape, and shows signs of gross overheating. If you look at the body of the resistor, it is badly crazed ( a term that referes to the fractured appearance of the outer 'shell' or body of the resistor. Also, damage in electronics is not always visible from the outside, so a quick look around to see if anything else is wrong can be, sorry to say, totally misleading. The resistors may not be the only problems, as mentioned before. There is an electrolytic capacitor that to me is suspect as well. It is in close proximity to one of those resistors, and there are signs of either leakage, scorching, or both near the bottom. For the boards to get discolored to the degree they are indicates that things got very, very hot in there.

[Marvel]

You'll notice, Bruce, I didn't refer to any specific part -- fuse or resistor, although I did mention the large capacitor.

You misunderstood me. The OP said fuse when referring to R12, and I thought you would have caught it. It wasn't meant as a criticism of you.

And yes, some of the parts certainly need to be replaced. I used to do repairs on three phase motor controllers, and circuits handling a lot of current. Some looked far worse than this board, and only needed connections resoldered. Some parts still measured correct, when they looked awful. We would usually replace them, for safety's sake. Plus, if the customer looked at them, they looked a lot better... []

Bruce

[hotsho111]

So I got a chance to take a good look at the board and the only odd thing I discovered was this. The C309 thing (I have no idea what it is) looks a little cooked. This is on the largest board in the sub where all the audio cables are connected. Not sure how big of a problem this is, but my wild assumption is this may be why one of my speakers was buzzing slightly. Either way, I'm going to replace the resistors this weekend and I'll let you all know how it goes.

Also, from my OP, I knew it was a resistor I just mistakenly called it a fuse.

[erik2A3]

Jeremy:

You had correctly identified other resistors, as well as the fuse, in other parts of your post, so it's obvious this was just a simple mix-up....easy to do. C309 is s surface mount capacitor, and SMT components can be kind of tricky to work with. With stuff like this, sometimes it's honestly easier, particularly if you don't have the correct equipment and experience to make the repair, to replace the entire board, although I know that must seem kind of drastic. So, if replacing just the resistors helps, that's good, but that little C309 guy has seen better days, and is not looking very good. It seems to me this is more than just a resistor going 'bad' which is kind of rare but of course not impossible. Whatever happened seems to have affected more than a single, isolated part of the circuit.

If you have doubts about anything, please get some help from someone who knows this equipment. Perhaps the manufacturer can help with this. Sometimes professional troubleshooting and repair can cost enough to make one consider a brand new replacement, which is not a slight to anyone. We all need to earn a living! erik

[hotsho111]

I'm just going to try replacing the resistors this weekend and hope all goes well. I'm kinda doubtful though because that C309 capacitor doesn't look so healthy. Any idea about getting a replacement for that? I'd be helpful if someone from Klipsch could chime in on that.

I'll let you guys know how it goes tomorrow after I replace the resistors.

On a side note, anyone know the difference between the v2.400 and v4.1? I have a v4.1 and found a replacement sub but it's from a v2.400 system. I'm not sure what differences there are between them.

[hotsho111]

It looks like that C309 SMC is a 10µF 25V capacitor. Anyone know how to remove and replace one of these. I've never dealt with one of these before, but have no problem doing it.

Edit: I looked it up online and it can be done with a regular soldering iron. Digikey has some but I'll check radio shack tomorrow to see if they have them. I'm going to replace them all before trying to see if it works.

[Marvel]

The main problem in doing the surface mount parts is how you can overheat them very quickly. They will be cheap, so you might want to get more than one. Make sure you have some low temp solder and don't bridge across the pads. A reasonably priced, temperature controlled iron is the way to go.

Bruce

[hotsho111]

Just to give everyone an update (in case this becomes useful in the future) radioshack had the resistors, but at too small a watt rating (1/2W). I just ended up ordering everything from digikey. Hopefully I get a chance to work on it this weekend

[hotsho111]

A little update, I replaced the r12 and r26 fuses without much trouble. The c309 smd I'm having some issues with though. In my overeagerness to remove it I pulled up the pad with it. I have no idea how to find one of those, or even how to replace it. Even if it was still there, the part I bought isn't the right one. The board is getting power though.

I think I found a board I can replace it with and I'll let you know how it goes.

[erik2A3]

Good job with the resistors. As mentioned, that cap had the potential for a little difficulty because it has to be removed, the connection area cleaned and solder flux removed, and the new part installed. That the pad has lifted does not necessarily mean you wouldn't be able to make a bridge with a fine piece of hookup wire connected to the same place the damaged part of the trace leads.

[Marvel]

That the pad has lifted does not necessarily mean you wouldn't be able to make a bridge with a fine piece of hookup wire connected to the same place the damaged part of the trace leads.

Agreed! Been there and done that.

Bruce

[hotsho111]

I was thinking of trying that as a last resort. One thing though, the surface mount cap I got is 10uf25v which is about 3 times the size (physically) of the ones actually on the board. I saw someone else with the same one blown (c309) and replaced it with a 100nF/50V one. I'm not sure how the sizing would go on these, but is that one physically smaller? Can you get the same measurements in different sizes?

As for repairing it, I've never heard of hookup wire, or how I would even repair that pad. My plan if I had no other ideas was just to fill that area with solder and then put the surface mount on that.