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KEF PSW2000 fault – fixed!

Discussion in 'Subwoofers' started by crispybig, Oct 2, 2004.

  1. crispybig

    crispybig
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    Just thought I’d post this for posterity in case it could help anyone in the future.

    My PSW2000 sub-woofer (part of the Kef KHT2005 package) died last night. The LED came on red and then green as normal, but zero sound. I noticed there was no click from the box shortly after power on, as there usually is.

    Opened the box this morning, and saw there was a small relay next to the speaker connections (blue, RLY1). Tracing the tracks revealed this switches the SPK+ output between earth and the amp output.

    Found RS had a direct replacement, stock number 369-488, £1.96. One quick trip to the RS trade counter and 10mins with the soldering iron later, and a fully working sub once more. :thumbsup:

    You can hear the relay click about a second after the green LED comes on if things are working OK.

    Hope someone may benefit from this in the future.

    Chris
     
  2. Nimby

    Nimby
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    Somebody ought to congratulate you. :)

    So it might as well be me! :blush:

    Try not to think of it as the consolation prize. :devil:

    I hope your sub was out of guarantee? :cool:

    Regards
    Nimby
     
  3. crispybig

    crispybig
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    Thanks - but your congratulations are premature.

    It seemed too easy to be true - it was! :mad:

    Worked fine last night watching a movie (home theatre setup). But this afternoon - dead again!!!

    Same symptoms:With power on and no input signal the LED is red (as it should be in "auto" mode). Give it some input and the LED turns green, then - nothing!

    No "click", so I assume the relay is not going over.

    I'd opened up the original relay just out of interest, and the n/c contacts were firmly welded together, with heavy black burn marks around the area. I can't for the life of me imagine how, just switching the amp output, but there it was. The contacts are rated at 240v a/c 10 amp! It looks almost like it had been switching mains to earth....

    I can't imagine the new relay has gone the same way after just one evening's use. I had cycled it several times and all was fine, clicks at the right times, etc. It didn't seem like the control circuitry was damaged at all.

    Guess I'll have to extract and autopsy the replacement relay. If it too is welded up I'll........ well, I don't really know. Probably bite the bullet and off to a dealer to check out (or anyone know if KEF service manuals are available?).

    It's well out of warranty btw. About 3 years old, bought off eBay a few weeks age (now I know why he was selling it!).

    Ah well, it was good while it lasted. :(

    Chris
     
  4. Toyboy

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    Ask KEF for advice
     
  5. johndoe1

    johndoe1
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    my psw2000 died on me after warranty had run out - told kef symptems... bloke said send the board back and we'll have a look. When I asked about cost he said that it will either be free or not cost much (parts only)

    got it back about a week later with several new components soldered on - capacitors resistors and triacs (i think) works a treat now.

    :smashin: Kef.
     
  6. Nexer

    Nexer
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    Sorry I know this is an old thread :oops:

    What happend to your sub? My PSW2000 is showing the same fault. I'm gonna try and replace the relay.
     
  7. FIXITNOW2003

    FIXITNOW2003
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    TIP no operation at all and the relay protect relay was not engaging
    The amp uses parallel pairs of 2SC5200's and 2SA1943's in complementary with all collectors tied together at the centre point. There is also a TA7317 speaker protect relay driver chip. I raised the mains input using a variac to give a +/- 10V supply and found that the centre point was at -10V. The main output transistors checked out ok and so did their drivers so attention was turned to the small signal transistor Q11 (MPSA56). This was found to be totally open circuit and its replacement restored the centre point to 0V. Now the speaker protect relay operates to connect the speaker and normal operation is restoredalso check the large capacitors
     
  8. Matt24

    Matt24
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    Hi,

    I found my relay RY1 faulty a while back. I found the relay on RS and fitted it. It worked for a short while and is nor behaving the same again. I did this before finding this forum and now my heart sinks.

    I really don't want to spend much money repairing it if possible.

    I was looking at the circuit diagram and the only role the relay 'seems' to play is to switch over when an input signal is detected. Why could we not cut the pins from the contacts of the relay and link the speaker into the circuit rather than have the relay do it? I wouldn't have thought it would be a problem if the sub was turned off it not in use.


    Any thoughts would be very welcome.

    Thanks

    Matt :hiya:
     
  9. TrophyJem

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    My guess is that if your replacement relay dies after a very short period of time, that there is DC on the output caused by another fault within the amp. If the woofer jumps from its natural power off displacement point to another position when the relay kicks in (with no audio supplied), then this would be a sure indication of this fault.
     

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