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Please help with repairing a faulty toy "laptop"

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David K.

New Member
Dear everyone. I'd like to ask your help with fixing this faulty Fisher Price V6999 toy laptop I'm struggling for a couple of days now.

  • Buttons 7, 8, 9 and the mouse doesn't work.
  • The last column of the 5x5 led matrix doesn't always work (seems like an independent contact problem in the lid)
  • It seems like the buttons are powered by two wires (violet and blue in the picture below) and neither of the buttons which are meant to be driven by blue are working.
  • I could measure a stable 3V all along the violet line but 0V along blue.
  • It seems like the button presses are handled in kind of a multiplexed way. The 10 buttons are using only 5 data wires and 2 power wires. I suspect these two wires should be powered alternately and the micro-controller decides whether it's a "two" or an "nine" depending on which one is active in the cycle.
  • If I connect 3V DC directly to the test point next to S2 on the red wire just briefly it either says "two" or "nine". It varies which one it is.
  • If I keep them connected for about half a second it says both "two" and "nine". Their order still changes. It can be "two"-"nine" or "nine"-"two".
  • It suggests to me that the cycles are properly handled in the controller. I think it couldn't say "nine" otherwise. However, for some reason violet is always powered and blue is never.
  • Using Poor Man's Oscilloscope I was measuring around and found that after pressing for example button 2 and the toy says "two" some kind of signal is sent around on the red line.
  • When pressing a button of the violet line at the test point on the left of R18 the voltage drops to ~1.5V from 3V (maybe the sound or display control signal is sent) At the point left of C8 there's an about 0.1V voltage drop for a second. At the point at U1 and the "1kHz test point" it's always 0V.
  • The top section of the left board is seemingly dedicated to controlling the 5x5 LED matrix. The two larger caps are probably driving the speaker. The 8 larger solder joints between the large caps and JR belong to the off-on(silent)-on(loud) switch on the back.

So here am I know. If you have any idea what may be the problem or what and where should I measure please let me know. I'm hoping it's rather a problem with some of the SMD components rather than the micro-controller itself.

Thank you in advance.

A bit better photo of the internals: https://s9.postimg.org/t1cfclar3/fp_v6999_02.jpg


Well-Known Member

Rather than measuring around, I would suggest that you look for bad solder points. It's most common around bigger components such as DC connectors and stereo outlets.

I also would have cleaned contact points (for buttons) on the PCB card, and also the rubber side of the buttons. Just be careful and don't use acid cleaners because some variants may get the rubber to shrink/deform.

The toy could also have being defect by static discharge by somebody touching the PCB card without properly grounding. If that is the case then it's a lost case trying to fix.

Even if English isn't my native language, I had to read your title twice as it wrongly suggest that there is the kid that have a defect - not the toy unit.

David K.

New Member
Thank you for the tips Grossel. I'll be checking the solder points. (And updated the title too. Hopefully it's not so misleading now :) )

Cleaning the button contacts may be also useful. However, I think the problem doesn't originates from worn contact because when I close them directly by wires on their test points the problematic buttons still don't work.
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