"Weird Device" : Nutone Door Bell LA60

[budm]

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.

[jasonbay13]

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.

i did adjust the blue pot, but did not touch the white one.

[budm]

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.

[goontron]

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.

[keeney123]

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.

[stj]

Re: "Weird Device" : Nutone Door Bell LA60

is the chipsocket good?

[jasonbay13]

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.

[jasonbay13]

Re: "Weird Device" : Nutone Door Bell LA60

pics

[jasonbay13]

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.

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.

[stj]

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.

[jasonbay13]

Re: "Weird Device" : Nutone Door Bell LA60

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.

[goontron]

Re: "Weird Device" : Nutone Door Bell LA60

What about the charcoal in the top right corner of the first pic?

[jasonbay13]

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?

[stj]

Re: "Weird Device" : Nutone Door Bell LA60

check the crystal is running

[keeney123]

Re: "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

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.

[jasonbay13]

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.