EEVblog #1219 - Don't Trust Switches - Toy Repair

Sagan's toy remote control wouldn't work, and it lead to a most unexpected fault that released the magic smoke.

#Repair #MagicSmoke

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[khutsomakgoka]

Finally! a repair video of a toy I can afford.

[bigclivedotcom]

It must be something we caught off YouTube. I've got a stinker of a cold right now too.

[bigclivedotcom]

Is it possible that the channel select switch was toggling an input between positive and negative, and was left in an intermediate position which shorted them both? The resultant heat as the switch melted could have melted through the wire insulation while also cooking both wires with the full battery short circuit current.

[demoncloud]

Moral of the story: If you gonna use Vcc for Logic High, kindly use a high value resistor in Series

[sprybug]

I wouldn't be surprised if that plastic switch, the one that controls the up/down (back/forward) motion, over time continuously rubbed against the white wire, rubbing away the coating, causing it to expose the wire to the ground chassis of the A/B switch.

[onemanshow]

Meanwhile:
Son: “Dad... Can you fix my remote control?”
Father: “Sure, let me get my camera”
Son: “Ok, dad. I’ll just be outside selling lemonade so I can buy a new one.”
...The pitfalls of having a YouTube dad. 😆

[richfiles]

**EDIT** And I see you caught that detail as well, at the very end of the video! I was starting to wonder just _HOW_ under the weather you were! XD
I believe they used the switch housing to save the cost of a jumper wire or 0 ohm resistor. One side of the switch is tied to the positive power coming off the power switch. The common goes to the chip, and the other side of the switch is tied to the switch housing next to it. the other side of the switch housing is tied to the battery negative. Basically, the switch either sets the chip input to the negative rail or positive rail. The switch housing was used as part of the circuit to avoid the need for a pull up (or down) resistor, a 0 ohm jumper resistor, or even a plain jumper wire. Gotta save those pennies!

[Graham_Langley]

Looks to me like the channel select line is switched between +V and 0V and the metal switch body is used as a jumper to get 0V to one of the switch contacts.

[toleranz]

So a simple 10k pull-up could have saved Sagan‘s day. Penny pinchers. Hope you get well soon Dave.

[theR]

Only Dave can make a video about a faulty switch, while sick, that lasts almost 10 minutes.

[Ken-oech]

I with Sagen. I think Huxley buggered the switch.

[mattelder]

I've almost never seen a metal cased switch on something that WASN'T tied to ground. That's normally done to prevent shocks.

[iPelaaja]

But there is an electrical reason to ground the switch body though, isnt there. The middle contact selects the channel depending on if it is connected to + or -. Because its a single side PCB, they somehow need to jump the ground over the signal, as you can see, the left contact is also connected to the case. So the chip looks for either + or -, but they need to get ground over the signal, so they go through the case.

[jugularSignal]

I'm getting a sore throat just hearing your voice. Get well soon Dave, great video as always.

[richardhead]

Kids can be some of the best cycle testers around.
I wonder if Sagan put a few thousand cycles on that switch while he was watching his favorite television shows.

[smunaut]

Switch probably failed at being"Break-Before-Make" and the wiper got stuck in some intermediate position where all 3 contacts were shorted. Seems more probable to me than shorting to the case.

[jasinere]

the inside if the switch is all plastic that holds a copper slider strip & whats happened here is the plastics broke apart the slider poped off into the gap shorting the switch terminals to the outside & even if you replace the switch the chances are one of the other components would have been burned out too cos of this short

[cuteswan]

My guess is that a bit of Huxley Drool™ got into the switch, shorted it, and that melted the wires together. I think the kid is going to be an ace product tester. ;) Anyway, I hope you're feeling better soon. Take care.

[fullwaverecked]

You're a good egg Dave! Keep fighting the good fight... and get well soon. We need you.

[locouk]

Hmmm.. you must be using too many batterizer battery boosters to get extra juice, the thing went critical and into meltdown!