Troubleshooting a PCB

uxphil 10 months ago

Hi, hoping to get a little help here with a basic PCB trouble shooting question

I have a kids toy here, which runs of 3aa batteries

it’s a roof of a train station that has two buttons and should make a noise when either is pressed

I get some noise, but not at all the right ones

i took it all apart and found this PCB.

i suspect one of the elements it busted.

question, how to I check whether the following are working

- capacitors

- resistors

- diodes

I’ve tested the speaker and it works

any other tips on how to troubleshoot this with an multimeter?

What order should I test in? And which settings?

thanks for any help!

Phil

Top Replies

0 beacon_dave 10 months ago

Can you add a picture of the reverse of the circuit board and showing the rest of the connections ?

Tracing the connections and making a rough sketch of the circuit as a schematic is usually helpful.

I'm seeing what looks like a battery box with power switch, a microphone and speaker with simple amplifier but don't see any button or power connections to the circuit board. Are the blue wires the button connections ?

Does the microphone work ? What sort of sounds are you expecting ? Is there another sound effects module ?

There is some residue and corrosion visible on the board so looks like something has leaked at some point.
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0 uxphil 10 months ago in reply to beacon_dave

Here you go
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0 beacon_dave 10 months ago in reply to uxphil

And there it is... a glob top COB chip producing the sound effects.

If that has failed, then you are likely looking at an upcycling project.
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0 bidrohini 10 months ago

Check for broken traces too.
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0 beacon_dave 10 months ago in reply to uxphil

Have you measured the voltage at the circuit board (red & black wires) when powered up ?

If it is significantly lower than the 4.5V expected, then you may find that the glob top doesn't work properly affecting your sounds.
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0 shabaz 10 months ago

Those two cylindrical electrolytic capacitors visible in the photo might have dried up. Probably worth replacing them, since that's a low-cost thing to do. Other than that, I can't think of anything much beyond what everyone else has already suggested. Worth just visually inspecting the board in case you see any failed solder joints (you could re-melt the solder, soak it off with braid, and then add some more, if there's any doubt) and that soldered wire connections still look good.

And, as beacon_dave mentions, the voltage should be checked (even if new batteries were inserted). I opened a pack of AA alkaline batteries, sealed, from Amazon, and was amazed that one was at 0.3V terminal voltage.
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