Hi,
I've been using a set of M-audio Bx5a monitors, and today -suddenly- one of them started "buzzing". It's not very loud, but it doesn't need to be loud in order to be disturbing
It still seems to be working - there's nothing wrong with the sound, but with the added buzz.
The buzzing is not related to the signal source (it stays there even when i unplug the cable), and it's at constant volume (it's not affected by the volume knob).
Now, keep in mind that, each of these speakers have its own amp circuit inside (actually two circuits in each - these are bi-amplified: separate amps for the tweeter and the woofer) , so by comparing the broken speaker to the other one, here are a few more differences in behavior:
- when i turn off the working speaker, its power led keeps glowing for a few more seconds before it goes off. But on the broken one, the led turns off instantly as i turn the power off.
-when i turn off the broken speaker, there's a very loud popping sound, but not with the other speaker.
What do you think could be wrong with the circuitry? I'm thinking it might be a capacitor failure (maybe in the power supply?) causing all this, but i'm not sure. If it's something as simple as that, i can just replace the broken component instead of sending it away for repair (which might take months).
Thanks in advance.
...
emre
I've been using a set of M-audio Bx5a monitors, and today -suddenly- one of them started "buzzing". It's not very loud, but it doesn't need to be loud in order to be disturbing
It still seems to be working - there's nothing wrong with the sound, but with the added buzz.The buzzing is not related to the signal source (it stays there even when i unplug the cable), and it's at constant volume (it's not affected by the volume knob).
Now, keep in mind that, each of these speakers have its own amp circuit inside (actually two circuits in each - these are bi-amplified: separate amps for the tweeter and the woofer) , so by comparing the broken speaker to the other one, here are a few more differences in behavior:
- when i turn off the working speaker, its power led keeps glowing for a few more seconds before it goes off. But on the broken one, the led turns off instantly as i turn the power off.
-when i turn off the broken speaker, there's a very loud popping sound, but not with the other speaker.
What do you think could be wrong with the circuitry? I'm thinking it might be a capacitor failure (maybe in the power supply?) causing all this, but i'm not sure. If it's something as simple as that, i can just replace the broken component instead of sending it away for repair (which might take months).
Thanks in advance.
...
emre
Thanks teemuk and Leolabs
I opened it up, and took this photo. As you can see, there seems to be something wrong with the cap on the right; it looks as if it's about to explode, not to mention it somehow managed to free itself from the glue. Am i safe to assume that this is the cap i should be replacing?
...
emre
I opened it up, and took this photo. As you can see, there seems to be something wrong with the cap on the right; it looks as if it's about to explode, not to mention it somehow managed to free itself from the glue. Am i safe to assume that this is the cap i should be replacing?
...
emre
If you can't see the attachment, here's the photo:
.
e
An externally hosted image should be here but it was not working when we last tested it.
.
e
Hi,
Seeing this pic there is certainly something wrong with that cap.
The top is bulging due to pressure inside, and the sooner you replace it the better. This will very likely cure the present problem, but I would have a careful look at all other similar caps in the circuit while you are doing some work on this.
After maybe 10 or so years (depending on use and cap quality), these electrolytic caps do deteriorate somewhat, and if I was doing this job I would replace any similar caps as a matter of course, because they will probably go the same way soon.
However, if the unit is only a year or two old, then maybe this was just a rogue cap, and the others should be OK for a few more years.
Regards,
Seeing this pic there is certainly something wrong with that cap.
The top is bulging due to pressure inside, and the sooner you replace it the better. This will very likely cure the present problem, but I would have a careful look at all other similar caps in the circuit while you are doing some work on this.
After maybe 10 or so years (depending on use and cap quality), these electrolytic caps do deteriorate somewhat, and if I was doing this job I would replace any similar caps as a matter of course, because they will probably go the same way soon.
However, if the unit is only a year or two old, then maybe this was just a rogue cap, and the others should be OK for a few more years.
Regards,
emremeydan said:
HI,
Be vary careful now that you have told me this, and at all costs, avoid switching the unit on whilst there is no cover on it.
With 'old' electrolytics, they tend to dry out over the years, so if and when they explode, there is usually less of a problem.
However, with newer caps, they will often spew out caustic electrolyte from within the caps when they fail like this, and it will make a real mess inside the unit. The greatest danger is if you are working over the unit when this happens and if your eyes are not covered at that time, you could end up with severe eye-damage!
Unless you purchased this second-hand, I would get back to the seller and get it properly sorted out, if it is as new you say. If you cannot do this for some reason and you need to do the repair yourself, assuming that the other other cap is potentially similar (probably from the same batch in manufacture) I would replace this at the same time, out of caution. Such caps shouldn't be too costly, and if one does later explode, it will certainly be a big mess and a lot more work to put this right.
Good luck.
Regards,
Hi,emremeydan said:
I'm glad to know that you will be careful here as I have seen some rather nasty sights when this happens.
No, I doubt that any explosions could occur when not being powered up, but I would still be cautious when working on these, and especially I would wait a few hours after the last time power was applied, as gasses could still be building up for a while.
Good luck, and do take care.
Regards,
It might be worth checking what the voltage across them is. 25V capacitors would suggest 18V supplies are being used, but i wouldn't be surprised if the rail voltages are 25V - too close to the limit. Check this in the working speaker.
If it's using 25V supplies, replace the capacitors (in BOTH speakers) with some decent quality 35V units. Go for a good brand such as Nichicon or even Panasonic.
If it's using 25V supplies, replace the capacitors (in BOTH speakers) with some decent quality 35V units. Go for a good brand such as Nichicon or even Panasonic.
Well, i replaced that cap and the problem is gone
I couldn't find a 6800 uf cap the size of the original one (all the ones i found were a bit bigger and wouldn't fit), so i used a 4700 uf cap which had the same footprint (a little taller, but that wasn't an issue). This cap is just for power supply filtering, so it shouldn't make much difference whether it's a 4700 or 6800.
I didn't replace any other caps, cause de-soldering the old cap turned out not to be so easy - the copper "dot" on the PCB got removed as i was desoldering the legs of the cap, leaving behind only a tiny area for soldering the new cap. I managed to solder the new cap to that tiny trace, but didn't want to take any further risks trying to replace the other caps (which look fine for now).
And Jaycee, thanks for the advice. Turns out there are L7812's inside, which suggests that the amp runs on 12V, so i used a 25V cap again. Of course, it could be that it runs on +12/-12V, so 25 might not be high enough to be totally safe, but i'd have to go with an even smaller capacitance value if i were to pick a 35v cap (or it wouldn't fit). Besides, every single cap in the circuit (there is a total of 10 or so electrolytics) is 25V rated. It probably will work fine under normal conditions.
And thanks Bob, for the info. Good to know that they won't explode when not powered - there are many caps on my desk these days (as i'm building a headphone amp on my breadboard)
...
emre
I couldn't find a 6800 uf cap the size of the original one (all the ones i found were a bit bigger and wouldn't fit), so i used a 4700 uf cap which had the same footprint (a little taller, but that wasn't an issue). This cap is just for power supply filtering, so it shouldn't make much difference whether it's a 4700 or 6800.
I didn't replace any other caps, cause de-soldering the old cap turned out not to be so easy - the copper "dot" on the PCB got removed as i was desoldering the legs of the cap, leaving behind only a tiny area for soldering the new cap. I managed to solder the new cap to that tiny trace, but didn't want to take any further risks trying to replace the other caps (which look fine for now).
And Jaycee, thanks for the advice. Turns out there are L7812's inside, which suggests that the amp runs on 12V, so i used a 25V cap again. Of course, it could be that it runs on +12/-12V, so 25 might not be high enough to be totally safe, but i'd have to go with an even smaller capacitance value if i were to pick a 35v cap (or it wouldn't fit). Besides, every single cap in the circuit (there is a total of 10 or so electrolytics) is 25V rated. It probably will work fine under normal conditions.
And thanks Bob, for the info. Good to know that they won't explode when not powered - there are many caps on my desk these days (as i'm building a headphone amp on my breadboard)
...
emre
Hi,
I know the problem you mentioned, and it is not unusual, unfortunately.
What I do if this happens and the solder pad is damaged or lost, is to bend the cap's lead across the PCB underneath, cut it to a suitable length, and solder it to a part of the trace which isn't damaged.
You will probably need to remove any solder-mask which covers the trace with a bit of careful scraping so that the cap's lead can be soldered properly, but I have never been beaten by this, and I have done hundreds of these jobs. Often you can bend the lead and solder it to another solder-pad nearby, but make certain that this other pad is directly connected to the damaged pad, of course, and that it cannot short out on to anything else.
When removing caps, I find it needs more heat usually than when soldering a new joint, and plenty of flux, and even adding some more solder temporarily can help to get these cap leads out quickly. The main thing is not to apply heat for too long as this will tend to cause lifting of the pads.
If the lead cannot be 'moved' freely within a couple of seconds or so, it isn't good to keep the heat on this area. It is better to begin again, maybe with more heat (a hotter iron tip, if it is variable temperature) or maybe with a bigger soldering iron.
Far more damage is likely in my experience if the iron is too small (not powerful enough) or at a too low temperature than using more heat and completing the de-soldering job quickly.
Incidentally, it would be unusual in my experience if you do have a +/- PS and for any one cap like this to be across *both* supplies. With large electrolytics like you have there I would guess that one is across the +12v, and the other across the -12v rails, so you will have plenty of margin on voltage-rating if this is so.
Sometimes a cap is added across both PS rails, but I have never seen anything large in value used like this, and it is generally a very small cap (maybe 1uF or less, and not usually an electrolytic cap, either) which is installed to help just with HF decoupling.
I'm glad that you have solved the problem, anyway.
Regards,
I know the problem you mentioned, and it is not unusual, unfortunately.
What I do if this happens and the solder pad is damaged or lost, is to bend the cap's lead across the PCB underneath, cut it to a suitable length, and solder it to a part of the trace which isn't damaged.
You will probably need to remove any solder-mask which covers the trace with a bit of careful scraping so that the cap's lead can be soldered properly, but I have never been beaten by this, and I have done hundreds of these jobs. Often you can bend the lead and solder it to another solder-pad nearby, but make certain that this other pad is directly connected to the damaged pad, of course, and that it cannot short out on to anything else.
When removing caps, I find it needs more heat usually than when soldering a new joint, and plenty of flux, and even adding some more solder temporarily can help to get these cap leads out quickly. The main thing is not to apply heat for too long as this will tend to cause lifting of the pads.
If the lead cannot be 'moved' freely within a couple of seconds or so, it isn't good to keep the heat on this area. It is better to begin again, maybe with more heat (a hotter iron tip, if it is variable temperature) or maybe with a bigger soldering iron.
Far more damage is likely in my experience if the iron is too small (not powerful enough) or at a too low temperature than using more heat and completing the de-soldering job quickly.
Incidentally, it would be unusual in my experience if you do have a +/- PS and for any one cap like this to be across *both* supplies. With large electrolytics like you have there I would guess that one is across the +12v, and the other across the -12v rails, so you will have plenty of margin on voltage-rating if this is so.
Sometimes a cap is added across both PS rails, but I have never seen anything large in value used like this, and it is generally a very small cap (maybe 1uF or less, and not usually an electrolytic cap, either) which is installed to help just with HF decoupling.
I'm glad that you have solved the problem, anyway.
Regards,
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