Author Topic: How does this diode work?  (Read 534 times)

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Offline naujoksTopic starter

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How does this diode work?
« on: October 02, 2024, 12:06:47 pm »
I'm trying to repair an early 90s PC PSU, which has no +5V.
There is a dead short on the 5V rail.
I found out that when I take the diode S30SC4M out of the circuit the short disappears.
I can measure a short between pin 2 and 3, but not between pin 1 and 2, so my assumption is that this diode is faulty.
I'm not familiar with this kind of diode and I'm interested in how it works. It seems to have two diodes wired against each other, so does that in effect make it a transistor, or a MOSFET?
Interestingly, when taken out, the PSU also doesn't have 12V output. Is that the expected kind of behaviour how it works, that it's responsible for the 5V and 12V output, and maybe the other voltages too?
 

Online langwadt

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Re: How does this diode work?
« Reply #1 on: October 02, 2024, 12:13:39 pm »
It's just two diodes in one package
 

Offline naujoksTopic starter

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Re: How does this diode work?
« Reply #2 on: October 02, 2024, 12:20:25 pm »
I see. So it makes sense then that the left hand side is in the 12v circuit and the (shorted) right hand side is in the 5v circuit.
 

Online langwadt

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Re: How does this diode work?
« Reply #3 on: October 02, 2024, 01:15:28 pm »
I see. So it makes sense then that the left hand side is in the 12v circuit and the (shorted) right hand side is in the 5v circuit.

the diodes are connected, 5V and 12V wouldn't be cconnected like that
 

Offline naujoksTopic starter

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Re: How does this diode work?
« Reply #4 on: October 02, 2024, 02:30:17 pm »
Is there any obvious reason why without that part the 12v line should disappear as well?
 

Offline coromonadalix

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Re: How does this diode work?
« Reply #5 on: October 02, 2024, 03:02:46 pm »
is the 5v derived from the 12vdc  and removing theses diodes kills it ??

is it possible to take some pictures or a crude hand sketch ?
 

Online wasedadoc

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Re: How does this diode work?
« Reply #6 on: October 02, 2024, 05:00:19 pm »
It's just two diodes in one package
Two diodes. Middle pin is their two cathodes.
 

Online fzabkar

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Re: How does this diode work?
« Reply #7 on: October 02, 2024, 05:55:22 pm »
 


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