Author Topic: Diode identification help  (Read 556 times)

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Offline quicknickTopic starter

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Diode identification help
« on: April 16, 2023, 11:30:33 pm »
Hello,

Can anyone point me in the right direction regarding this diode?: (pic 1)
The rings seem to be red-red-'something' (first red band is the cathode), where 'something' looks either greenish or bluish depending on the light...

It is removed from a vintage video card that I'm repairing (Asus GeForce 2 GTS), where it failed in a half-shorted state, leading to the burning of R22 from the schematic below (pasted here from the US3007 datasheet). Problem is that the datasheet doesn't mention anything about such a diode (I've added it in red to correspond with the implementation on the Asus board): (pic 2)
The board works just fine after removing the diode and replacing the burnt resistor, and the Nvidia reference implementation doesn't use the diode and also does away with the 10 ohm resistor, but one has to wonder, did Asus install the diode for no reason? (pic 3)
 

Online Kim Christensen

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Re: Diode identification help
« Reply #1 on: April 16, 2023, 11:39:51 pm »
Maybe it's a 14V Zener diode? Red Red Green?
See attached datasheet:
 
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Offline quicknickTopic starter

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Re: Diode identification help
« Reply #2 on: April 18, 2023, 10:26:23 pm »
Thank you, that must be it! I'm ordering a few...
 

Offline ppTRN

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Re: Diode identification help
« Reply #3 on: April 19, 2023, 10:52:45 am »
The US3007, in the pin description section, says for the V12 pin (pin 28):

This pin is connected to the 12 V supply and serves as the power Vcc pin for the output
drivers. A high frequency capacitor (typically 1 uF) must be placed close to this pin and
PGND pin and be connected directly from this pin to the GND plane for the noise free
operation.

Since the pin is already connected to 12V I am betting that the diode is a zener for over voltages protection, that's why it works fine widout it
 
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