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electric recliner chair problem

Discussion in 'Troubleshooting and Repair' started by peskycats, Jan 27, 2014.

  1. peskycats

    peskycats

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    Jan 27, 2014
    I am trying to fix my recliner chair, it is a two motor job with Dewert hardware and electronics. I have narrowed down the problem to two burnt out relays (removed and marked by large red circles on pcb). I also see that the 2 protection tr's going across the relays coil (I think) are damaged so suspect they have exceeding their duty cycle / time of just 2 mins in 18 mins - probably by my grandchildren using my chair as fairground ride.

    I would like to know the chips proper identity and what it exactly does (data sheet etc) to help me draw up a circuit diagram for future needs (and to keep my brain busy).

    I know the inputs come from the hand controller (4 for up/down of back and feet) and have traced those but would like to know the inner workings.

    I think I have traced the 6CW on the tr's to possibly BC817 transistors and they are in a SOT23 package I believe.

    Any help would be most welcome indeed.
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,249
    1,746
    Sep 5, 2009
    hi there, Phil

    I have moved your post to its own thread

    for future reference, It isnt a good thing to hijack some one elses thread

    cheers
    Dave
     
  3. peskycats

    peskycats

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    Jan 27, 2014
    I hadn't realised that I had 'hijacked' someone elses post.

    I can repair just about any computer but I have not used a forum to post in myself so it is a steep learning curve. Maybe you should not assume that everyone knows how to use your site when you reply to them.

    I took the trouble to read as many 'stickies' that I could find, including finding a new post button but alas didnt find one.

    I certainly do not find your remark user friendly and if this is how you communicate to new users then maybe I have chosen the wrong forum after all!:mad:
     
  4. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    Life is one long learning curve. Have another look, you will find a new post button. It is neater to keep the subjects separate, particulary for search purposes.
    One of these next years, I will find how to quote a previous post!

    I find it strange that both the relay drive circuit and the relay itself have failed. If the relay has failed, then the load has been too great. You can check the current with a meter to see if the contacts are underspecified.
     
  5. peskycats

    peskycats

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    Jan 27, 2014
    All I see is 'Post Reply' unless its somewhere else, I checked 'Home' - not there!

    Like I said its not user friendly if you dont use these and approaching 70 i dont usually do so bad !

    One thing I got to learn pretty quick in my teaching days was to know your audience so you know at what level to start with them. Surely you should cater for all ages and experiences.

    As regards the relays they are up to the job but not to children using it as a fairground ride. They are now banned!

    My main point is finding data on the chip as I stated so I can finish my diagram of it which may well then help others to find their way round as I know of a few places that would welcome it. Dewer are very secretive of it, it seems.
     
  6. davenn

    davenn Moderator

    13,249
    1,746
    Sep 5, 2009
    Hi ya Phil

    don't take it personally :) you would have got the same response in any other electronics or any internet forum for that matter,
    its just about learning forum etiquette

    No big hassles :)
    when you are within a persons thread, you get that green "post reply" button up near the top left of the thread ... and that's what you did in some one elses thread :)
    its called thread hijacking ie starting/posting a topic totally irrelevant to what that thread is about

    When you are in the main forum index, and you can see the various forum subsections ... general chat, microcontrollers, circuit help etc and you choose the subsection suitable for your post ... in this case the repair section - that green button at the top will be "New Thread"

    all in the fun of learning :)

    typing BC817 datasheet into google will bring up a datasheet for that transistor

    cheers
    Dave
     
    Last edited: Jan 28, 2014
  7. duke37

    duke37

    5,211
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    Jan 9, 2011
    I think I have sorted the quote system.

    You are a mere chicken at under 70. You will need to run pretty hard to catch me up :)
     
  8. peskycats

    peskycats

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    Jan 27, 2014
    Duke37: My running days are well over and am not looking to catch anyone up, just still expect the common courtesy that once was!

    Davenn: I already have the data sheet on the 6CW (maybe BC817) and havn't asked for it. The chip is something else and have now exhausted all the links in the welcome sticky on searching hence mky question. I was just trying to give some background to my problem but maybe too much info is not a good thing in some areas. I usually find it very helpful when trying to help people. I really don't see this site as being what I was looking and hoping for so please delete my info.

    If all forums are like this (they aren't thank goodness) then heaven help us!
     
  9. davenn

    davenn Moderator

    13,249
    1,746
    Sep 5, 2009
    well you havent shown us the actual chip number

    if you are referring to the chip in the middle with the sticky tab on it
    it would be helpful to see the actual chip # that number on the sticky is probably just the firmware version ... you need to carefully peel that off and read the actual chip type on the chip
    THEN you may have some luck from google and from people on the forums ;)


    cheers
    Dave
     
  10. duke37

    duke37

    5,211
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    Jan 9, 2011
    I was implying that you are much younger than me.

    You say that there are tr's across the relay coils. I have never met a tr's, perhaps you mean a transistor. The transistor is much more likely to be in series with the relay coil to switch the current. There is also likely to be a diode across the coil to limit the voltage on switch off.
    The relay can be tested with a supply of 20V on the coil. 10V may be enough to actuate. If the contacts are damaged, it may be possible to clean them. Do not use emery paper as the emery can get embedded in the contact, stopping conduction.

    Providing a supply direct to the motor will determine whether the motor has failed.

    I do not understand the time limitation, this is more likely to be temperature rise dependant in the motor rather than in the relay.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
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    Jan 21, 2010
    When Dave used the work "hijacked" he was using it in a technical not pejorative manner. I think you've read more into what he said than what he intended. It's not easy to tell from a single post exactly how much experience a person has or whether they're likely to take offence.

    Although you had some difficulty finding the correct button, Dave has given you your own thread. He did this because (1) it removes any distraction from an existing thread, and (2) it makes sure that you get relevant responses.

    Your thread has got several people's attention, so if you still need help, we're here.
     
  12. gorgon

    gorgon

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    Jun 6, 2011
    The two ringed Components are transistors driving the relays. The black round Components marked '4007' to the right of the transistors are the protection diodes. There is a Tx mark for the transistors, and a Dx mark for the diodes.

    You say the relays have burned out. Is the contacts burned or is the coil burned out?
    Even if the transistors are burned, the microcontroller could still be ok. Try to replace the transistors, and the relays. You should also check the motor before you reconnect the control module.
     
  13. peskycats

    peskycats

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    Jan 27, 2014
    I have now fixed my chair. The CW6 Tr (we always referred to transistors as tr's in my time at Thorn's) was blown and I changed the accompanying relay too for good measure despite measuring ok.

    I had already said that I had proved the motor was ok by switching them round (it has two motors). I had removed the two relays from one motor as highlighted on the picture in order to continue using the chair albeit in a limited way.

    Dewert say the run time for these controllers is just 2 mins and then have to rest for minimum of 18 mins. So I suspect my grandchildren caused it when they used it as a play thing - no more!

    So I can now relax again in comfort.
     
  14. duke37

    duke37

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    Jan 9, 2011
    Good that you have got it going.

    I do not understand the time limits. The thermal time constant of a small transistor will hardly likely be longer than one minute so two minutes will in effect be infinitely long. The thermal time constant of a massive motor will be several minutes so perhaps this is the reason for the 18 minute cooling time.

    It is better to use simple english without abbreviations, some users use translators to get to their own language. The abbreviation which annoys me most is 'tx' which can mean transistor, transformer, transmitter or transceiver.
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
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    Jan 21, 2010
    Not entirely :)

    The transistor and the surrounding board will have some thermal mass. Thus when pump heat into it, it will rise in temperature at a certain rate (not immediately as the degC/W figures for heat dissipation might suggest). [edit: it will rise up to the limit determined by the balance between heat entering and heat leaving the system -- this is what degC/W means. That rise is not linear. You would find part of the equation looked something like Tf *(1 - e^(-t/tau)) where f is the final temp, t is the time, and tau is a constant that is related to the thermal mass of the system.]

    I would guess that the transistors are being driven well beyond the limits for the amount of heatsinking provided, and the designer has relied on thermal mass and duty cycle to keep the transistors out of danger.

    This is either poor design or a method of saving a small additional cost per unit (and possibly both).

    Depending on the circuit, one could imagine replacing what are almost certainly bipolar transistors with either a larger part (able to dissipate more heat) or a mosfet which would drop less voltage at the current required to operate the relay. Either approach would require some investigation into how the transistor is driven.

    However, peskycat's solution of keeping the kids off it should make this a moot point :)
     
    Last edited: Feb 1, 2014
  16. gorgon

    gorgon

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    23
    Jun 6, 2011
    I've checked the datasheet of the relays, and the coil is only rated to 360mW for operation, and that's 18mA at 20V. The BC817-40 is rated to 500mA, so I can't see how the transistor is burned out here, even if badly trashed.

    It could be that the 4007 protection diode is too slow and repeated activation will induce peaks of reverse voltage through the transistor, nagging it to Death. :D

    Of course, as the transistor is rated for 200mW, if turned on very slowly, it could be that this rating can be broken, and heating the transistor at repeated activations. That is a very bad design, however.
     
    Last edited: Feb 1, 2014
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