I have a Kef PSW 2500 that emits a loud buzz when on. I pulled the amp, but I'm not sure if its the speaker or amp. What should I be looking for the speaker outputs from the AMP? How can I tell if its a grounding issue?
Audio Players & Recorders - KEF Audio - PSW 2500 Subwoofer
Answers & Comments
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.
My father gave me this subwoofer and simply said "its broken, fix it and its yours". Thank you for this post!!! I'm an EE, so I can say that this fix was simple, but it may be more difficult for others that aren't as skilled with a soldering iron. I ended up changing C52 to a 100uF 85C cap (its all we had on hand at work). I kept the leads long on the cap to try and get it away from the power resistors. So far its been working like a charm.
Two things I would do differently:
1) If I were to buy a cap, I'd get one with a higher thermal rating to try and avoid the obvious heat issues that are in this section of the board.
2) I am a bit concerned that the heat sink compound should be replaced. I may come back after getting some arctic silver to clean up this job.
Happy fixing!
THANKS A LOT !!!!!
I had the same buzzing on the 2500 after five years and KEF told me it was the relay that needed fixing. It costs £113 to repair and this includes it being sent back to you.
Fantastic, it worked for my PSW 2010 which had the buzzing sound...
:-)
If this is a powered sub, then when the amp is not connected and it emits the buzz, then it's the sub that's at fault. It's perhaps a capacitor inside that's doing it. Have a look inside. Suspect the largest Electrolytic Capcitors first.