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With short circuit pulled, back to operating on "final straw".

unsubstantiated -

Imagem da história

Meu Problema

My friend's Acer Chromebook C710 stopped working (caused by a drop). It would no longer turn-on. It showed no sign of life: no little indicator light when mains + battery connected, no faint sound during instant power button is pressed.

I knew it contained a short circuit. Its AC adapter power supply emitted a very brief faint noise roughly every second or two. This "black plastic power brick" features short circuit (over current) protection: it was trying to supply power, but it would immediately shut-off, then wait a brief period (one – two seconds) and retry.

I disassembled this C710, removed its motherboard. I found a little (SMD 0402, 1 × ½ mm) component which had POOFed, exploded. It was burned-away, not problem short circuit. I had to keep looking, to find problem short.

Minha Solução

With my eyes I could not find what was shorted. I learned from a tutorial video by Louis Rossmann '2ND TRY: How to find a short circuit in a macbook logic board.' how to locate a shorted component by injecting power and feeling for heat. I used two PP3 ("nine volt battery") as current source, and alligator clips and multimeter probe to make connection. (One PP3 supplied around half ampere, which made a portion of board warm, but no single hot spot. Two PP3 in series supplied around one ampere, which allowed one component get hot enough to feel by hand.)

One ceramic capacitor short circuited, gets hot. I guess that, when it shorted it resulted in that little 0402 to POOF!. I consulted a schematic which jayeff found. ( [Acer Chromebook c710] How do I replace the charging chip? ) This cracked, shorted, capacitor seems to be one of identical PC101 or PC102: 4.7U_0805_25V6-K. It is visibly cracked, but I did not notice its crack until heat directed my attention to it.

I do not have a handy spare of such capacitor. And I read, SMD capacitors are difficult to hand-solder (they often crack when hand-soldered). So I only removed this old bad one. I did not replace it with a good capacitor. I used a soldering gun to remove this bad cap, by pushing it aside (I want to say, plowing, bulldozing, shoving).

I reassembled Chromebook, tried to turn it on. Success, it turns-on! Now it might be operating in bad health, asking for trouble, "on thin ice" "on a thread" on a "short fuse" "final straw". With two capacitors missing, circuit components might be working overly hard, or components might be supplied "dirtier" input. Like pulling teeth and bloodletting, missing capacitors (I think!) is bad. But if I did not find this short circuit, then I would have replaced whole board. So to continue "using up" this board's life is better than whole-replacement.

Meu Conselho

Next time you hold a computer motherboard which is dead with a short circuit, don't immediately chuck and replace it. Thought of hunting for a short circuit might be daunting, but don't shy away from it. If your plan is to discard and replace it whole, then what do you stand to lose? In my story (Chromebook C710 motherboard), there were no subcomponents to possibly damage, so I had no fear. During my story I felt really adventurous.

After all I had fun, felt proud and accomplished. I learned what a cracked ceramic capacitor looks like, so I might more easily spot one, next time. Best of all, this motherboard is being reused. All of its connectors have more mating cycles, its clock will have zillions more ticks, its microchips will perform zillions more calculations, and all other parts will see further use, before eventually being junked.

This project costs are: time (mine), electricity (soldering gun), milligrams of material waste (capacitor).

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wow,good to know

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