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Old 03-13-12, 12:09 PM   #1
Treason
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Red face Transistor knocked off on PCB, how can it still be running?

I was doing some cleaning of the bookshelf and while sweeping one level something clattered on my hardwood floor. To my surprise it was a transistor (coffee brown rectangle with silver ends). I used to put all my redundant video cards there going back years.

I have a retro P3 1 GHz running an Asus GeForce2 GTS 32 MB AGP video card. It's running games like Quake2/3, Quake Live, Wolfenstein ET, late 90's OpenGL stuff. Also used for downloading.

So I was curious and took out the video card. Sure enough, one of the transistors on the back of the video card GPU core was knocked out. The missing transistor matched.

How can this video card be even running? Especially one of the GPU core transistors? This is a video card that has been running for a few years now!

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Old 03-13-12, 12:46 PM   #2
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Default Re: Transistor knocked off on PCB, how can it still be running?

Hmm, I just soldered it back on. I was wrong, it's a resistor, so that's why the card is still running. I'm just surprised it's one of the core resistors.
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Old 03-13-12, 01:52 PM   #3
T.h.o.m.a.s.
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Default Re: Transistor knocked off on PCB, how can it still be running?

resistors should be black
capacitors brown ( thats what you prolly knocked off , often used for noise supression etc, that could be one of the reasons why it worked without it )
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Old 03-13-12, 03:38 PM   #4
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Default Re: Transistor knocked off on PCB, how can it still be running?

Capacitors have a polarity. I guess you got your 50/50 guess correct because the card is working now.
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Old 03-13-12, 04:03 PM   #5
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Default Re: Transistor knocked off on PCB, how can it still be running?

Quote:
Originally Posted by ViN86 View Post
Capacitors have a polarity. I guess you got your 50/50 guess correct because the card is working now.
Most electrolytic capacitors has a polarity but not all of them. Other capacitors has no polarity at all.

Just sayin'

Looks like this?
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Old 03-13-12, 04:11 PM   #6
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Default Re: Transistor knocked off on PCB, how can it still be running?

Quote:
Originally Posted by lduguay View Post
Most electrolytic capacitors has a polarity but not all of them. Other capacitors has no polarity at all.

Just sayin'
Meh, the capacitors I've dealt with had a polarity. Either way he's lucky.
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Old 03-13-12, 11:03 PM   #7
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Default Re: Transistor knocked off on PCB, how can it still be running?

Yes it looked exactly like that. Luckily there was some solder snapped off on both ends so I matched it to the solder remaining on the PCB.
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Old 03-15-12, 01:10 PM   #8
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Default Re: Transistor knocked off on PCB, how can it still be running?

yeah, probably just a decoupling capacitor.
The goal of those is to reduce noise and supply current during spikes (smooth current variation).
If you have good power delivery, knocking it off should have very little effect.
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