SMD parts

[ramondo]

Looking for some insight to smd part problems.
1 Does anyone know if specific parts fail from non use on a regular basis (res goes high or low while being unpowered)
2 How is EEPROM data ORIGINALLY installed to device.
3 Does anyone have info on terms used on schematics(ex. zcr210_ad.... used to describe a resistor. What does ZC or AD mean)
4 Does ferrite bead resistance equal dc resistance or impedance at a specific freq.

[diif]

Re: SMD parts

1 No, components don't usually fail without power, maybe an excess of heat but that's poor storage. Parts fail due to an excess of current, voltage or ripple or a combination.
2 With a programmer of some sorts.
3 Got a screen shot as an example ? Perhaps there is a component list to go with the schematic to help identify the parts.
4 Yes the impedance quoted is for a certain frequency.

[stj]

Re: SMD parts

a ferrite bead should have no resistance - it's a bead on a short wire.

coiled / wire-wound inductors have larger resistances.

[diif]

Re: SMD parts

Yeah, D'oh ! It's inductance not impedance. Henries, Millihenries and Microhenries.
I've just pulled similar sized ones off dead boards when I've needed some and they've always worked. (No comebacks).

[eccerr0r]

Re: SMD parts

Then again inductors also have frequency dependent impedances, just like capacitors... Just that larger inductors have higher ESRs unlike capacitors (at least for electrolytics) where it tends to be the other way around...

I do wonder how many of these jury rigged inductors (meaning, adding a ferrite bead) were carefully calculated versus being a wet finger calculation to at least somewhat attenuate the spikes, reducing high frequency noise...

[stj]

Re: SMD parts

i suspect a lot of circuits with beads - like digital stuff or mosfet gate-pins are a case of something not working and a guy with a scope trying to kill a glitch followed by a design-change.

[diif]

Re: SMD parts

The ones i replaced recently were on the 19v line just before the LVDS connector. Vaporised when screens were changed and the battery not removed.
I'm not sure how critical the closeness to the original needs to be.
I couldn't find a schematic so it didn't matter anyway.

[stj]

Re: SMD parts

probably just to stop noise from the led invertor going back into the laptop.