Looking for schematic for Cambridge Soundworks P300HD subwoofer

[Childof70s]

I own a P300HD subwoofer built and sold by [the now defunct?] Cambridge Soundworks. After 12 years of use, the subwoofer will no longer power up. Looking at the input board, I see that one of the capacitors is smoked (C618). I'm seeking a schematic so that I can determine the value of C618 and how it is incorporated into the circuit.

Does anyone have any insight as to where I might locate and obtain the schematic?

 

[Eppie]

No schematic on-line that I can find. If you unsolder the part can you remove it to see if you can read the value? If not, see if the circuit is symmetrical. Perhaps there is a matching part of equal value that you can reference. If this is part of the power supply then the exact value is not critical if it is just a filter cap. Bear in mind that something caused that cap to blow. There may be other damaged components. Subwoofer amps are often covered in goop to prevent vibration and are notoriously difficult to repair.

Here's a story of someone who tried to have it repaired. He lived near a former CS engineer who simply replaced the entire circuit board. That's usually the only fix available.

 

[TLS Guy]

I own a P300HD subwoofer built and sold by [the now defunct?] Cambridge Soundworks. After 12 years of use, the subwoofer will no longer power up. Looking at the input board, I see that one of the capacitors is smoked (C618). I'm seeking a schematic so that I can determine the value of C618 and how it is incorporated into the circuit.

Does anyone have any insight as to where I might locate and obtain the schematic?

View attachment 51504

I came up empty.

Unfortunately service manuals these days do not often exist, and if they do are released to no one, and kept proprietary.

I have a couple of comments.

1. Smoked components are more often than not the result of the failure and not the cause.

2. Sub amps with their switching power supplies are a nightmare to service, and frankly usually impossible.

The unit does not seem to me to be one worth going to to a lot of trouble over.

Was it part of some type of HTIB system? I suspect it might have been.

Either way my advice is to cut your losses and move on.

 

[Childof70s]

Thank you both for Insight. Sounds like I'd better give up unless I happen to stumble upon somebody that has the replacement board I need.

 

[colofan]

If it is a typical switching supply. need to replace the FET's on the switcher and replace all of the caps in the power supply circuit. If you have the time and a DMM you should be able to debug. Another source is the local HAM group could help out with the electronics.

 

[jose.hernandez]

I own a P300HD subwoofer built and sold by [the now defunct?] Cambridge Soundworks. After 12 years of use, the subwoofer will no longer power up. Looking at the input board, I see that one of the capacitors is smoked (C618). I'm seeking a schematic so that I can determine the value of C618 and how it is incorporated into the circuit.

Does anyone have any insight as to where I might locate and obtain the schematic?

View attachment 51504

This might be a little late but my P300HD just died after 12 years as well. I went exploring, but it wasn’t the C618. Here’s a pic of the clean C618 if it helps

 

[ROMzombi]

Does anyone know if the OP repaired this? I have the same C618 cap burned out. It appears to be the only thing burnt on the board.

 

[Eppie]

Does anyone know if the OP repaired this? I have the same C618 cap burned out. It appears to be the only thing burnt on the board.

You know as much as we do from the above thread. The prior post shows the cap at 250nF 250V. Something made your cap blow, though. As colofan mentioned, I would first be looking at the FETs and diodes for the switch mode power supply section and check for any shorts. Inspect all caps for deformities. Repairing a switch mode power supply can be as easy as replacing the electrolytic caps but when a cap blow out like that you likely have a short somewhere. Not the kind of repair I would recommend for a novice to repair. Be sure to discharge any caps before working on it. There can be some high voltages in there.

 

[ROMzombi]

I've been staring at the board and really see no other burnt, leaking, or deformities in any of the components. If the board isn't fixable i'm tempted to connect the subwoofer to my car (suv) stereo sub amp and hear what it sounds like.
* can shorting input cause that cap to blow like that? No that would not make sense.

This was given to me so I don't know what happened to it. What about shorting the power source input? Or some power surge in mains. This is also marked "risk of fire replace fuse as marked". I don't see any typical fuses on the board. If there were wouldn't it have saved that cap?

 

[Eppie]

I've been staring at the board and really see no other burnt, leaking, or deformities in any of the components. If the board isn't fixable i'm tempted to connect the subwoofer to my car (suv) stereo sub amp and hear what it sounds like.
* can shorting input cause that cap to blow like that? No that would not make sense.

This was given to me so I don't know what happened to it. What about shorting the power source input? Or some power surge in mains. This is also marked "risk of fire replace fuse as marked". I don't see any typical fuses on the board. If there were wouldn't it have saved that cap?

Parts do not always show physical signs of damage when they break down. If you don't know how switch mode power supplies operate and can't diagnose a circuit board with a multimeter then this is likely beyond your ability and at worst could be dangerous. These circuits sometimes use a grey fuse resistor instead of a glass fuse and they need to be measured. A surge could damage the unit but a failed cap could just as easily cause the power supply to fail. It's unlikely anything on the input caused the damage.

Car audio speakers tend to be designed differently from home audio components. I would not expect that unit to make a decent car audio sub.

 

[ROMzombi]

Yes, it is different being that each woofer is 17 ohms. I like the size of the cabinet and that there is potential to move air with more combined surface area than what I'm presently using.

 

[TLS Guy]

Yes, it is different being that each woofer is 17 ohms. I like the size of the cabinet and that there is potential to move air with more combined surface area than what I'm presently using.

If that is a 17 ohm driver, then that unit is a boat anchor.

 

[Eppie]

This sub wouldn't need this since the cabinet doesn't vibrate at all. You can't feel any vibration even down to 35 Hz.

The sub wouldn't need what? The glue they use to cement down components? You can not judge what is happening inside the enclosure by trying to feel cabinet vibrations. Speaker cabinets are designed to be nonvibratory. There is plenty of air movement inside a ported cabinet and temperature variations cause components to expand and contract. Manufacturers would not waste money on gluing down components if it was not required.

 

[TLS Guy]

The cabinet is sealed. No part of the amplifier is inside the sub enclosure. Since the sub enclosure does not vibrate, I hardly think the amplifier, being outside the enclosure, is going to suffer damage.

It is not that simple, as sound travels through solids 17.5 times faster than air. But speed still equals frequency X wavelength. So a 30 Hz tone in the air of the enclosure and the room, will be a 525 Hz tone in the solids of the box, circuit board and components. So vibration can certainly occur.

So as sound travels through different mediums its frequency changes according to the density of what it is passing through.

Sound travels 4.4 times faster in air than water. So the frequency of sound traversing water has its frequency increased 4.4 times.

 

[BassResonance]

Does anyone know if the OP repaired this? I have the same C618 cap burned out. It appears to be the only thing burnt on the board.

I can't speak for the OP, but I have the same C618 burnt up. I did replace it, tested, immediately heard some hissing, which I thought was a capacitor leaking (about to burn up/smoke), so I unplugged it. I don't think the repair was complete. *I also replaced one of the MOSFETs in the PS section, as it had slightly different resistance readings than the identical one next to it. I had them on hand, so why not, I thought. It's not exactly a shotgun repair, but close! Anyway, I'm missing something else that's bad, I guess. I haven't given up yet. The hissing sound was odd, especially since this failed cap looks to be in the power supply section. I just haven't gotten my mind wrapped around this amplifier circuit yet.