20 Most Recent KEF Audio PSW 2500 Subwoofer Questions & Answers

I have experienced the problem of the output cutting out in a KEF PSW2500. I have also previously replaced C52 which is mentioned in previous posts and is the storage capacitor to power U13 that protects the speaker from direct current in case of fault. The problem of cut out at high volume levels occurs on my unit as follows: When the input level is high in bass content, regardless of the input level (VR1) setting on the back of the unit, the output has a loud pop and stops until power is recycled, or just pops loudly on peaks but will recover. If I remove one channel of the input the problem is much less apparent. The previous C52 fix corrected the buzzing noise caused by the protection relay coming on and off when the capacitor was dry, but the new problem is slightly related as follows: The audio operational amplifiers (opamps) make up the filter and gain stages and are powered by a +/-15V supply composed of U14 and U15. If you measure the -15V output (this can be done without the speaker connected and using a VOM) you may see that its output will go to 0V during peaks or may lock at 0v while the +15V side is stable. If you do measure this, the result is that the output of the opamps will have DC on them instead of 0V, causing U13 to detect this and shut down the output to the speaker to avoid damage. Cause: The cause of this problem is due to the lack of input capacitors in the original design, between the Vin pin and ground of the voltage regulator IC's which in some cases can lead to latch up of one of the regulator IC's; especially the negative regulator (U15, LM7915). This part is not defective, but just latching up due to instability in the design. Fix: To fix this problem, you need to add some components as follows: For simplicity sake, I used the same 47uF/63V parts that are used in the C52 repair. You need to solder 2 pieces in parallel with Vin and ground of U15, making sure the minus side of the capacitor is to the input and the plus side is to ground. Secondly, you need to solder 1 piece to the Vin and ground of U14, where in this case the minus side will go to the ground and the plus side to the input. Note: If you get the polarity wrong, the capacitor will blow up due to overheating. The reason that you unbalance the capacitors, is so that you make sure the positive regulator comes on first and then the negative regulator second. This is well documented by the manufacturers of the parts so it is not new. Since this instability may be due to parts ageing, you may also want to add 1 piece of capacitor at each side of the +/-15V connector on the preamp board side, which is labeled CN2. This will make sure the audio circuits still have a healthy filter on the supply to keep the audio nice and clean. Note that the ground is common between the supplies so CN2 is only 3 pins. You can test the unit without the speaker connected first with some high level content while re-checking the 15V supplies. Both should be stable and the protection relay should only come on when powered up and stay engaged anytime there is music content. If that checks out, re-assemble the unit (remembering to connect the red and black speaker wires) and enjoy your new sounding sub-woofer.

Have just repaired a similar problem with a KEF 2500 - relay was chattering at 50 Hz rate, buzz in speaker output.

Problem was caused by overheated / dried out Electrolytic filter cap (C52 - 47uF 63V) on the relay coil supply feed.
The overheating is caused by adjacent power supply dropping resistors which run very hot due poor design of power supply.

A service manual for a similar model is available at following link, refer to power supply section:-
http://www.eserviceinfo.com/downloadsm/35375/kef_psw2000.html

To replace,
1) remove chassis from speaker cabinet (8 screws), disconnect red/black speaker wires from main PCB spade connectors.
2) Remove 4 screws attaching main pcb heatsink assembly from face panel - lift assembly from faceplate (a bit messy , much heartsink compound between mounting faces)
3) unplug the AC 3 pin connections adjacent to the large capacitors and the 3pin connector on end of pcb (near C52), then roll assembly over the top of the audio sub-board to access underside of pcb.
4) solder connections to C52 is accessible at edge of board without further dis-assembly.
Take extreme care replacing C52, as the circuit board is of poor quality, (usual domestic electronics quality) being single sided copper without plated through holes.
The board is already heat damaged by heat buildup from power supply resistors, so the track will most likely lift and crack when disturbed- to counter this problem link the +ve capacitor pigtail to an adjacent solder pad on the same track.
Assembly is reverse of above, take care to preserve/ensure minimum disturbance of heatsink compound.

Just for clarity, I need to explain what the four inputs are on the KEF subwoofer. There is a left and right RCA input which is the input signal to the subwoofer and there is a left and right RCA output which is the High Pass output from the subwoofer. On the back of the Yamaha receiver, you said you have a subwoofer output. This output is most likely the mono subwoofer part of the home theater system and can be used if you like. The left right signal input into the KEF is summed into mono so if you only connect one channel you will basically reduce the signal level by 1/2 (-3dB) but it will work fine. Alternatively, if your Yamaha receiver has monitor out and monitor in, you can run the monitor output signals to the subwoofer and you can then run the high pass outputs from the subwoofer back to the monitor in. This will give you the subwoofer and provide a smoother signal matching with your audio system. It is not always easy to connect the subwoofer up to an integrated receiver/home cinema system using the high pass channels of the subwoofer as you don't always have access to the analog output and input of the front channels. In this case, just use the Subwoofer output or just the monitor out only. I hope this solution is helpful.

This symptom is most likely due to RLY1 (protection relay) not coming on. The purpose of this relay is to give some time for the circuits to settle during power up to avoid a "pop" noise as well as to detect DC in the output that may cause damage to the speaker. If there is a fault condition, this relay may stay off so there will be no sound. Note that the LED indicator for auto on/off is not driven by this relay so that is why you get an indication of signal even though you have no output. If you don't hear the relay click on, this may be the problem. It may also click on and off again. One quick thing to try is to have music playing into the unit before you power it on. Power it on for 1 second and then power off and see if you hear any output, even for a short time. This tells us that the speaker and amplifier may be OK, but the power supply is having problems. You need a VOM to check the following: (all measurements are referenced to ground) (speaker does not need to be connected) (be careful of the mains supply voltages) 1. Check to make sure you have around 50Vdc at cathode of D10 (side with the painted line on the case of the diode). This is the power supply to the relay. 2. Check connector CN2 and make sure you have +/-15V. The center of the connector is ground and this is a 3 pin connector, so each side will be a rail voltage. If either voltage is not close to +15 or -15, the relay may not come on. 3. Check anode side of D9. This should be close to 0V if the unit is normal, and close to 50Vdc if the unit is in protect mode. If the unit is in protect mode and 1 and 2 look normal, the power amplifier has DC and is most likely damaged and will need some expertise to repair. If all seems normal and there is no output, the speaker may be burnt out. You can put the VOM in ohmmeter mode at the lowest ohm setting and measure the resistance of the voice coil which should measure below 10 ohms and above 2 ohms. When connected to the meter, slightly push on the cone and you should see the measurement change value slightly indicating that the speaker is probably not at fault. If 1 above is normal, but 2 is not, look up (on FIXYA) how to fix this model when it cuts out at high levels as this fix should also work. If after applying this fix, the rails are not the correct voltage, you may need to replace either of the regulators U14 or U15. Trouble shooting is the only way to approach this problem, but is you stick with it, you should have enough information to pinpoint the problem which will lead to the correct fix. Good luck.

I have a 3500 and after 2 months it failed. I have an electrical engineering background but I am not a tech. I noticed that that the design has some small capacitors that lay right beside some rectifiers on the power supply. The rectifiers heat up the caps and they blow. My brother in law is a tech and replaced and upgraded the caps, moved them away from the heat source and it seemed to solve the problem. I don't know how the amp would survive without these fixes. My other option was going to buy a separate subwoofer amp for $200 because I like the rest of the unit. I bought a Bryston 4B from him for 500 bucks and he threw the repair in for free.

I HAVE FOUND THE SOLUTION THANKS

Sounds like bad capacitors in power supply.you`ll need to take it to a repair shop if your not handy with lectronic parts and tools

HI,go into the yam setup menu and make sure you have the sub turned on and cross over set to about 80hrtz if this suits your speakers,set sub level to about -5 on amp and say half way on the sub,this should work if not pull out sub cable at amp and touch the end,you should get a hum,if not you may have no power,faulty cable or sub.
PS>make sure you are pluged into the sub PRE OUT and NOT the six channel in.
Hope this helps.
CABLE GUY.

Either you need new high quality cables,or your amp has output filter capacitor problems.

Check main fuse or power cable.