NEFF S5456 Dwasher circuit board fried

Discussion in 'Appliances' started by stockwood, 30 Dec 2010.

  1. stockwood

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    Hi,

    My 9 year old Neff S5456 dishwasher gave up the other day. According to my wife it went pop (shortly after switching it on) and then started to smell a bit and hasn't shown any signs of life since. Incidentally it also tripped the mains elec.

    I've taken it apart and found that the circuit board is fried in a couple of places. The copper track has vaporised and a couple of components have exploded.

    So, it sounds starightforward to simply get another board and replace it, but as it will cost around £150 for this I'm a little cautious about assuming it is the board that has just given up on it's own, and not been caused by a fault somewhere else. I'd hate to put a new one in and fry that in the same way.

    The reason I'm cautious is that a day or so before, I felt it wasn't working just quite right. It was going through it's cycle without problem but during it's 25 minute drying period it had a faint sound of a motor/pump running. There was also a faint ticking from around the base...the only reason I heard it was because I knelt down to listen more closely to the motor/pump.

    Does anyone have any experience of fried circuit boards and whether it's likely to have been caused by another fault or can offer any other advice?

    Any info on the problem and good places to get new and used spare parts is appreciated.

    Thanks.
     
  2. zipper

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    Fried pcb's can certainly be caused by other electrical components shorting out, but they can also fail on their own. It is important to check for other failed components before replacing the pcb. Do you have any more information on your model? A service or product number would be very useful...look on the door lip for a sticker.
     
  3. stockwood

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    It's a S5456X1GB/12.

    Looking at the PCB I can see that the tracks that have been burnt are
    "UEB2" pin 2
    "VER1" pin 4

    I've traced "VER1" pin 4 (grey with black line) to a connector right underneath the unit at the back in the middle hidden away so it's difficult to see what it connects into without dismantling the body from the base. It looks as though it goes into a 4/5 way connector into the back of the main sump.

    I haven't traced "UEB2" yet but on the PCB it's the track through to L1 that's burnt out. Not sure what the L1 component is.
     
  4. zipper

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    UEB2 & VER1 don't ring any bells. Could you post a good close-up photo of the pcb (component side up) & mark (or describe) where the burnt tracks are? Did you notice if any of the triacs are burnt or damaged? (or one is missing small piece of its surface). There should be 7 triacs on the board (small black devices with 3 legs on one side & 1 on the opposite side). Failing some sort of identification you'll have to follow the wiring to identify possible culprits.
     
  5. stockwood

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    I've traced UEB2 back to the main power switch. If the colour coding of the supply cables is per UK standards (Brown Live - Blue Negative) then it's the switched negative that runs to UEB2 pin 2. This is one of the tracks that has fried, in this case up to the L1 component.

    Incidentally the insides of the mains power switch are still intact albeit the contact points are a little black due to effects of the fault.

    One of the Triacs has broken up and has fried the track up to VER1 pin 4. This is the cable I can't trace fully until the body & base are separated.

    I've uploaded a few photos and identified the fried bits.
     
  6. zipper

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    UEB2 terminals 1 & 2 are the power supply to the pcb. I believe VER1 terminals 1 to 6 control the "water points" system. If I am correct in my assumptions then I suspect a worn seal has allowed water into the synchronous motor assembly that controls the alternate operation of the upper & lower spray arms. See here for an explanation of the "water points" function http://www.diynot.com/forums/viewtopic.php?t=248887&highlight= If this is the case then it is bad news. For your own peace of mind I would still check the physical wiring to make sure. I think I am right in my diagnosis, but to save you a very expensive repair I do hope I am wrong in this particular instance.
     
  7. stockwood

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    Thanks zipper. This sounds the logical cause as there is water in the base that I know wasn't there 6 months ago when I had it apart for another fault.

    I'll strip it down and trace the wiring to confirm.

    If it is water leaking through the seal to the assembly can the seal be replaced or must the whole assembly (approx £90) be replaced?
     
  8. zipper

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    For your sake I hope I am wrong (it won't be the first time). Apart from being a god awful job to change out the instantaneous water heater, it is also expensive. Detergent charged water can be corrosive. If a leaking seal has allowed water to enter the workings the mechanism over time I doubt if you will get away with a patch-up. I suspect the blown triac you see on the board is the one that controls the small synchronous motor inside the water points. A triac is in essence just a simple switch but when one blows it usually means that the device it switches has short circuited. In my opinion it would be economically questionable to change out both the pcb and the complete water heater assembly on a 6 year old machine. This is the pcb on your machine http://www.espares.co.uk/part/dishwashers/bosch/p/1083/856/0/0/759497/dishwasher-control-module.html Fingers crossed...I hope the reality of the situation is better than the prognosis :D
     
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  9. stockwood

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    Stripped it down today and sure enough the blown triac does control the motor for the spray arms.

    I opened up the motor assembly and it had a good amount of water inside (the water is glissening in the attached photo) and you can also see dirty water stains on the underside of the motor housing (see other photo) so it had penetrated through. It's frustrating that a simple rubber seal caused £250 worth of damage.

    Considering the cost of the replacement parts, it's age (9 yrs) and that this seal is likely to be the first of many to go, I'm reluctantly going to scrap it. :(

    Have just ordered it's replacement for delivery on Friday. :D

    Thanks for all your help.

     
  10. zipper

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    Thanks for the feedback. At least you can console yourself with the fact that you didn't waste a bunch of money on a new pcb just to have it blow again...because that is what would have happened. Its a shame to scrap a machine all for the sake of a defective 20p o-ring but think you made the right decision. Better luck with the new one :D
     

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