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"Weird Device" : Nutone Door Bell LA60

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    "Weird Device" : Nutone Door Bell LA60

    i've got an old LA60 door chime i'm trying to fix for an 'old' friend.
    when power is applied the speaker pops, but from what i've been told it should make the default chime sound when powered up.

    the key pad seems to only partially function as i can sometimes get 3's, 5's, or 7's to appear on it's two digit display. but nothing more.
    on removal of power the speaker again pops. i am getting 5v to the keypad ic and nutone ic.

    i have tried some audio from my phone to after the driving tansistors before the amp and it will play sound, so i know the amp pat is good.

    assuming the nutone ic plays the default chime on powerup, i can only think that it is bad since the keypad also does not seem to work properly.

    attached is the manual with schematic.


    thanks in advance. if i dont get it working i plan on using an arduino with an mp3 shield to make a suitable replacement.
    Attached Files

    #2
    Re: "Weird Device" : Nutone Door Bell LA60

    Originally posted by jasonbay13 View Post
    i've got an old LA60 door chime i'm trying to fix for an 'old' friend.
    when power is applied the speaker pops, but from what i've been told it should make the default chime sound when powered up.

    the key pad seems to only partially function as i can sometimes get 3's, 5's, or 7's to appear on it's two digit display. but nothing more.
    on removal of power the speaker again pops. i am getting 5v to the keypad ic and nutone ic.

    i have tried some audio from my phone to after the driving tansistors before the amp and it will play sound, so i know the amp pat is good.

    assuming the nutone ic plays the default chime on powerup, i can only think that it is bad since the keypad also does not seem to work properly.

    attached is the manual with schematic. .
    thanks in advance. if i dont get it working i plan on using an arduino with an mp3 shield to make a suitable replacement

    If you have a scope you can go on Z106 to see if y1 thru y5 and X1 thru X4 are working. The 6805P2 in an old Motorola Processor,https://en.wikipedia.org/wiki/Motorola_6800

    So Z106 is a character generator for the keypad. Most likely you could ohm out around the keypad and Z106 perhaps for bad component. Key pad could have internal short or diode is bad or electrolytic going to Z106 is bad. I have not read the theory of operation. Just taking a quick look that is what it looks like. So glancing at the theory it is a 4 column 6 row matrix key pad. the 4 rows have a strobe coming from the Z106 when a key is pressed Z106 determine what column and corresponding key was connected and the it reads it as an Y input.
    So the other thing if you press the keys and get different sounds on your iPhone then perhaps the display is bad or a bad connection. In that case you can go to the theory of operation for the display and it will tell what highs and lows will be going to the display with the key is pressed. Remember to let your finger off of the key after you press it because that is when the processor reads it. You also have a volume control and a auto mute.
    Last edited by keeney123; 12-10-2016, 06:30 PM.

    Comment


      #3
      Re: "Weird Device" : Nutone Door Bell LA60

      check the crystal is running

      Comment


        #4
        Re: "Weird Device" : Nutone Door Bell LA60

        looking around the crystal and main chip i noticed this: (pic)

        i'm not sure what this is or how it happened, but before i do anything and possibly break it more... i've got a few pics for you to look at. i've circled the point of interest. also i've noticed the whole ground trace is bubbled.

        it looks like both traces exploded?
        Attached Files

        Comment


          #5
          Re: "Weird Device" : Nutone Door Bell LA60

          What about the charcoal in the top right corner of the first pic?
          Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....

          "Dude, this is Wyoming, i hopped on and sent 'er. No fucking around." -- Me

          Excuse me while i do something dangerous


          You must have a sad, sad boring life if you hate on people harmlessly enjoying life with an animal costume.

          Sometimes you need to break shit to fix it.... Thats why my lawnmower doesn't have a deadman switch or engine brake anymore

          Follow the white rabbit.

          Comment


            #6
            Re: "Weird Device" : Nutone Door Bell LA60

            Originally posted by goontron View Post
            What about the charcoal in the top right corner of the first pic?
            that was the first thing i noticed and thought perhaps the 5v had died. or maybe the heat from over 30 years had done it. that 5v regulator is regulating from ~22v after all.

            Comment


              #7
              Re: "Weird Device" : Nutone Door Bell LA60

              the circuit has been modified,
              the charing is from the 5v regulator using the pcb as a heatsink (poor design)
              it probably needs resoldering.

              Comment


                #8
                Re: "Weird Device" : Nutone Door Bell LA60

                Originally posted by stj View Post
                the circuit has been modified,
                the charing is from the 5v regulator using the pcb as a heatsink (poor design)
                it probably needs resoldering.
                i really should have taken pics of the front, too the regulator is on a small heatsink that seems to have a solder pin on the back.

                i'll grab a pic of the front tomorrow.

                Comment


                  #9
                  Re: "Weird Device" : Nutone Door Bell LA60

                  pics
                  Attached Files

                  Comment


                    #10
                    Re: "Weird Device" : Nutone Door Bell LA60

                    put the scope to the lead on the cap and i saw a sine wave that is somewhere around 1 cycle every 3 divisions at .1us, that would be about .3us/cycle = ~3.5mhz? my scope is really old and uncalibrated, and i said .3us, but it appears to be slightly faster, so it appears the crystal is working.

                    Comment


                      #11
                      Re: "Weird Device" : Nutone Door Bell LA60

                      is the chipsocket good?

                      Comment


                        #12
                        Re: "Weird Device" : Nutone Door Bell LA60

                        So on the two pictures I have mark up potential problem. The top board has a bunch ceramic disk caps and one surge protector. These caps are to low in the board and they have to much stress on the leads. Often times these caps will crack inside. Sometimes you will see and outside crack. Many times if you go to desolder these then they will split. These caps are made to be up off of the board this then will put less stress on the legs and when heated to soldering temperature they will not crack. The back side I have marked points were they leads are bent to another pad. This should be verified on the schematic to find out if it is suppose to go there. If you post the pictures of the scope then we can have a look.
                        Attached Files

                        Comment


                          #13
                          Re: "Weird Device" : Nutone Door Bell LA60

                          ^ If you look at the boardview on the PDF, that mod on the bottom looks to bring an older revision of PCB to match the newest.
                          Last edited by goontron; 12-11-2016, 11:19 PM.
                          Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....

                          "Dude, this is Wyoming, i hopped on and sent 'er. No fucking around." -- Me

                          Excuse me while i do something dangerous


                          You must have a sad, sad boring life if you hate on people harmlessly enjoying life with an animal costume.

                          Sometimes you need to break shit to fix it.... Thats why my lawnmower doesn't have a deadman switch or engine brake anymore

                          Follow the white rabbit.

                          Comment


                            #14
                            Re: "Weird Device" : Nutone Door Bell LA60

                            BTW, the Volume pot R112 is set to full counter clockwise. Did someone adjust that pot?
                            Also check the R123 pot, it looks like it is also set to Full CCW.
                            Last edited by budm; 12-12-2016, 10:45 AM.
                            Never stop learning
                            Basic LCD TV and Monitor troubleshooting guides.
                            http://www.badcaps.net/forum/showthr...956#post305956

                            Voltage Regulator (LDO) testing:
                            http://www.badcaps.net/forum/showthr...999#post300999

                            Inverter testing using old CFL:
                            http://www.badcaps.net/forum/showthr...er+testing+cfl

                            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                            http://s807.photobucket.com/user/budm/library/

                            TV Factory reset codes listing:
                            http://www.badcaps.net/forum/showthread.php?t=24809

                            Comment


                              #15
                              Re: "Weird Device" : Nutone Door Bell LA60

                              Originally posted by budm View Post
                              BTW, the Volume pot R112 is set to full counter clockwise. Did someone adjust that pot?
                              Also check the R123 pot, it looks like it is also set to Full CCW.
                              i did adjust the blue pot, but did not touch the white one.

                              Comment


                                #16
                                Re: "Weird Device" : Nutone Door Bell LA60

                                If the Volume pot is set to FCCW, then you will get the sound that is fed to that pot due to the wiper of the pot is at GND.
                                Never stop learning
                                Basic LCD TV and Monitor troubleshooting guides.
                                http://www.badcaps.net/forum/showthr...956#post305956

                                Voltage Regulator (LDO) testing:
                                http://www.badcaps.net/forum/showthr...999#post300999

                                Inverter testing using old CFL:
                                http://www.badcaps.net/forum/showthr...er+testing+cfl

                                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                http://s807.photobucket.com/user/budm/library/

                                TV Factory reset codes listing:
                                http://www.badcaps.net/forum/showthread.php?t=24809

                                Comment


                                  #17
                                  Re: "Weird Device" : Nutone Door Bell LA60

                                  Originally posted by jasonbay13 View Post
                                  i did adjust the blue pot, but did not touch the white one.
                                  So you could actually measure the resistance of the pot setting to make sure it is not set at gnd potential. You would do this with no power applied. Also, where are the colored wires attached too?
                                  Last edited by keeney123; 12-12-2016, 04:47 PM.

                                  Comment


                                    #18
                                    Re: "Weird Device" : Nutone Door Bell LA60

                                    I would just set it to 12 O'Clock for now.
                                    Never stop learning
                                    Basic LCD TV and Monitor troubleshooting guides.
                                    http://www.badcaps.net/forum/showthr...956#post305956

                                    Voltage Regulator (LDO) testing:
                                    http://www.badcaps.net/forum/showthr...999#post300999

                                    Inverter testing using old CFL:
                                    http://www.badcaps.net/forum/showthr...er+testing+cfl

                                    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                    http://s807.photobucket.com/user/budm/library/

                                    TV Factory reset codes listing:
                                    http://www.badcaps.net/forum/showthread.php?t=24809

                                    Comment


                                      #19
                                      Re: "Weird Device" : Nutone Door Bell LA60

                                      Originally posted by keeney123 View Post
                                      So you could actually measure the resistance of the pot setting to make sure it is not set at gnd potential. You would do this with no power applied. Also, where are the colored wires attached too?
                                      You can set it at 12 O'clock as Bud M suggested, but I would measure it there in resistance with no power applied. That will only take you a second to do and if the pot is bad. Meaning the resistor of the pot is shorted, which I have seen, then you will save yourself a lot of grief.

                                      Comment


                                        #20
                                        Re: "Weird Device" : Nutone Door Bell LA60

                                        this doesnt really make sense. z105 controls not only the sound, but also the display. the display will show numbers (not always the one i press), seemingly never a few of them, such as 8 and 0 and a few more. this could be a bad keypad, but then why is it when i hit the test button the display does not go blank like the manual says it should. (test button works confirmed by measuring resistance between 5,6 on keypad. this makes me think either only part of the z105 is dead, bad socket as stj suggested (how to tell?), or z106,z107,or z108 causing problems though this would make me wonder if it would stop z105 from playing the default chime on power, assuming it does in fact do this by itself.

                                        edit: just tried shorting keypad pins with a bit of wire. 2 and 9 are '0' and 4 and 9 are '1'
                                        whenever i short 2 and 9, i get '1' or '3' most often random, never '0'. but shorting 4 and 9 almost always gives me '1' as expected.

                                        i also noticed that pin 12 on z106 has 3k resistance to +5v while powered off? found this while checking to see if any buttons were bad.

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