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I am trying to repair this simple toy firetruck with a button, a speaker, a motor and some lights. First the sound stopped working, and now there is no light or motion either.

Overview picture of firetruck

All the wire connections seem to be solid, and I have confirmed the 4.5V from the 3 AA batteries between B- and B+ on the circuit board. The capacitors on the bottom both seem OK.

At this point I am stumped. I am a fair hand at soldering and I'm sure I could replace any of the conponents on the board, but I don't know how to continue the troubleshooting. My 2 year old son would be very grateful for any help :D

Circuit board top side Circuit board bottom side

Vegard
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  • Nothing obvious. Start probing voltages. – winny Oct 31 '23 at 12:36
  • is something getting hot? – EeEmDee Oct 31 '23 at 12:38
  • @winny any suggestions for which voltages to probe? C4 is reading ~4.5V and C3 less than 1 volt. I am not sure what to check and what to expect the values to be. – Vegard Oct 31 '23 at 12:51
  • @EeEmDee nothing gets hot – Vegard Oct 31 '23 at 12:51
  • If you are determined, go full bigclivedotcom and trace out the entire schematic and look up datasheets for the ICs. From there you may be able to determine something probe-able. Quick and dirty would be to just replace the electrolytic capacitors, but I doubt it would help. – winny Oct 31 '23 at 13:07
  • You might try checking that the wires are ok - you should get under 3 ohms with your multimeter measuring each wire at its ends. Another trick is to try to operate the toy and push/poke/prod things with your finger and see if something happens - that would indicate a loose connection. Make sure you touch the battery negative first so you don't ESD the board. – Smith Oct 31 '23 at 13:59
  • PCB tracks at the hole near R1 don't look good. – user107063 Oct 31 '23 at 13:59
  • @winny 2022.07.01 print looks like a date used as a version. If that's the case, the caps did not have a lot of time to deteriorate. Unless they are heavily underspecified or used with the wrong polarity, that would be a rather untimely death. – user107063 Oct 31 '23 at 14:03
  • @user107063 I agree. As far as degradation goes, capacitors would be first so if OP is handy with a soldering iron, it could be a quick check. I still doubt it though. – winny Oct 31 '23 at 14:19
  • Since it gradually started dying I'd suspect the voltage regulator. Cheap consumer electronics won't have TVS and the like, yet the motor could potentially spew out a bit of transients - maybe that has damaged/killed the voltage regulator IC (probably U2?). Regular ESD from when changing the batteries could cause similar problems. – Lundin Oct 31 '23 at 15:16
  • Can be the voltage regulator or the other ic. Don't lose your time and do yourself a new board with three buttons, – Fredled Oct 31 '23 at 16:14
  • Did you confirm the battery voltage under load? A bad battery will often read near it's rated voltage with no load but drop significantly when loaded. – GodJihyo Oct 31 '23 at 16:43
  • Thanks for all the tips. In the end it started working again after I mucked about for a bit - I still can't find any loose wires so while I might try resoldering them all, if it stops working again I'll certainly check the voltage regulator – Vegard Nov 02 '23 at 06:55

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There isn't anything obviously wrong. When it comes to this kind of electronics troubleshooting, you basically need to check things until you find something wrong.
You have to just be methodical about it. Personally I start with the easier things to check, and work through the more complicated. ie

Check continuity for all wires.
Check for shorted capacitors/resistors.
Check the resistance of the motor.
Disconnect the motor and check it runs with an external supply.
Check the outputs of any regulators.
Check the inputs/outputs of any ICs for proper operation. Sometimes it's easier to replace them than to figure out if they're working properly, assuming they don't require programming.
Check anything else you can think of.

LordTeddy
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