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How to debug this sound COB circuit?

alaasalama

Apr 2, 2021
3
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Apr 2, 2021
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Hi guys!
So, my kid has this "Animals Sounds Book" which is broken and doesn't produce any sound now, although the batteries are good.

I've attached two images showing the COB circuit, but I'm beginner and I don't know how to trigger these metal strips to test the output?

Also, any general idea about how to debug this board would be appreciated, wiring diagrams or what to search for?
 

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PETERDECO

Dec 19, 2019
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Dec 19, 2019
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Welcome to the forum. Start with the basics. You need to make sure the circuit board is getting power and that the speaker is good. A multimeter is a must.
 

alaasalama

Apr 2, 2021
3
Joined
Apr 2, 2021
Messages
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Thanks!

Yes, I have a multimeter, when the power button is "on", I can measure the voltage between the black/red wires, and it's around 5 volts, also this voltage is the same on different parts of the circuit.

The speaker has 8 ohms written on it, so when I checked that, it gave me around 14 ohms, is that bad?

Also, I was looking for a way to trigger these meta strips to activate the sound, do you have any idea how to do that? I was thinking of something like applying an external voltage on it or whatever that makes the circuit thinks this metal part is clicked!
 

Martaine2005

May 12, 2015
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Show a picture of the back side of the board.
There must be a common connection on that strip somewhere.

Martin
 

Bluejets

Oct 5, 2014
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6,901
These are similar from Ebay....might get you started.
 

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Nanren888

Nov 8, 2015
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Speaker?
The speaker has 8 ohms written on it, so when I checked that, it gave me around 14 ohms, is that bad?
With the circuit turned off; no power applied, and you put the meter on Ohms, and put the probes across hthe speaker, do you hear a click?
If so, that confirms the speaker is still there, which is likely.
.
Switch?
You say you can see the 5volts around the circuit when the swicth is on? So that's after the switch?
Should see voltage between black and orange whenever the battery/power is applied. After the swict, middle pin, only when "on".
.
Whats the battery? Is it a 5 volt battery?
.
After that?
Solder giving up? crack on board. Boards do sometimes tend to develop cracks that break the tracks on any area that gets flexed, by for example, press to play buttons.
.
Buttons?
Do any parts work? For example some buttons only?
Maybe the least reliable will be the connector to the buttons to play, or sometimes the buttons. Where rthat flexible PCB meets and connects to the rigid PCB?
If there is an opton to reseat the connector with a little movement to clean it up a little, you could try this.
 

Bluejets

Oct 5, 2014
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With the circuit turned off; no power applied, and you put the meter on Ohms, and put the probes across hthe speaker, do you hear a click?
If so, that confirms the speaker is still there,

Would require an analog meter or digital set to "diode" would it not..?
 

alaasalama

Apr 2, 2021
3
Joined
Apr 2, 2021
Messages
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Thank you so much guys! Although I'm still beginner, but you gave me some hints!

The answers:

- No, the speakers doesn't give this clicking sound, although I've applied all your steps.
- I'm sorry, the voltage is there regardless of the switch.

The book was working fine, then some buttons were working and others not, then the voice was cracking, not clear, then no sound at all.

I'm adding some more pics, and a YouTube video (perhaps you get an idea?)
 

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Nanren888

Nov 8, 2015
622
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Not familiar with the edge connections of these units.
A slow failure of some buttons first sounds like either
(1) switch/button failure (common)
(2) Connector failure (also common)
.
Maybe someone who has used these can help, but likely the buttons connect between the edge connector lines.
These might be scanned, so might show only short pulses.
Unfortunately shorting the wrong ones might not be good for it.
.
If you clean the connector surfaces, do you get any buttons working?
.
You could try to find out some of the connections the buttons make. That is use your meter on the button side, not the circuit side. If you can find two on the button-side connector that are open when no button pressed and connected when one of the button is pressed, then you would know a pair of edge pins that are normally connected when that button is pressed.
Then you could connect those two together on the module, for example with an alligator clips lead. These often have sharp teeth that might get through any oxidaiton or such that makes the connector dodgy.
.
If anything works with this, then it suggests that button is ok and the connector is suspect.
 
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