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Old 05-07-2020, 06:18 PM   #21
nickBcap
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Default Re: 20 pin 8A on HP 250 G4 mb - voltage regulator?

What does a resistor symbol with a line drawn the bottom points of the resistor symbol joining only those points mean? In the schematic along the AC_LED line is the symbol with the figures; 0_0402_5% > ACIN LED. Could this be an unnecessary resistor here?
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Old 05-08-2020, 12:10 AM   #22
emestee
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Default Re: 20 pin 8A on HP 250 G4 mb - voltage regulator?

Quote:
Originally Posted by nickBcap View Post
What does a resistor symbol with a line drawn the bottom points of the resistor symbol joining only those points mean? In the schematic along the AC_LED line is the symbol with the figures; 0_0402_5% > ACIN LED. Could this be an unnecessary resistor here?
This is a technical jumper - essentially a jumper wire in a resistor package. There used to be a resistor there during development. It has been replaced in the final version. The meaning of the specification is 0 Ohm (i.e. no resistance - jumper wire), 0402 SMD package, 5% tolerance (this comes from the resistor that actually used to be there, of course tolerance is meaningless if your resistor is 0 Ohm). The line indicates that it's a jumper.

Sometimes technical jumpers are left in place deliberately so that they can be removed during repairs, cutting off a a section of the board.
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Old 05-08-2020, 12:26 AM   #23
emestee
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Default Re: 20 pin 8A on HP 250 G4 mb - voltage regulator?

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Originally Posted by nickBcap View Post
Thank you for the plain English explanation.
The first Dual Uni-Directional ESD Protection Diode, 3-Pin SOT-23 before the first MLCC is shorting and also the MLCC is shorting. But somehow power is getting to the second Dual Uni-Directional ESD Protection Diode and to the rest of the board. Trying to make sense of the motherboard schematic pdf.
Don't refer to the components by their type, but rather by their designations. It makes it much easier for you and us to find them on the schematics. For example, the diodes on the piece you posted are PD1 and PD2. Note that many manufacturers use the P prefix to signify that this is a part of the power distribution scheme. D1 and PD1 are, therefore, two different unrelated components.

Shorting just means that the electricity is getting through unimpeded or with very little resistance. There's still the question of what the current is and where it goes. Additionally, shorts are sometimes partial (i.e. the component provides less resistance than it should, but not 0), or conditional (i.e. the component only shorts when it is overheated or physically deformed).

Note also that the diodes you are talking about are Zener diodes. They are different from normal diodes in that they're intentionally designed to work in reverse bias mode, because they produce a predictable voltage drop in reverse bias, which makes them great for ESD protection, as they would let through any excessive voltage, thus draining it to the ground and protecting the circuit. Thus, they may behave differently even if shorted. How did you test them exactly?

PD1 and PD2 in your schematic are unrelated. One is responsible for protecting the LEDs from static discharges. The other however appears to be a part of the charger identification circuit. My guess is this is on a separate tiny power connector board? You should probably post the full schematics.

Last edited by emestee; 05-08-2020 at 12:32 AM..
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