ATX power Supply - Broken Zener Diode

Thread Starter

Gemmy101

Joined May 18, 2020
5
Hey All,

I have old ATX PS and I am trying to fix it and then will convert it to bench PS.
after checking the PS, I found a broken Zener (or exploded) next to a broken resistor.

I can guess the resistor value as it is not completely damaged, but the Zener is coming our in pieces and need your experience guessing it if that is possible

The resistor is 150K Ohm Carbon Film

Both are located just after the full-bridge rectifier and the 400V capacitors, there is 2Mohm resistor then the Zener and resistor in question
20200518_024818.jpg20200518_024804.jpg
 

AlbertHall

Joined Jun 4, 2014
9,882
I expect there will be an IC in that part of the circuit board. Can the marking on any such IC then we will have some idea what we are dealing with.
A warning: these things are dangerous when powered with the lid off and that/those big capacitors will hold a charge which will at least hurt.
Also this is a switch mode supply which are difficult to repair even with a schematic.
 

Thread Starter

Gemmy101

Joined May 18, 2020
5
The closest thing that might be voltage related is the C2335
can that be related?
Zener was between B and E legs which is 7V rated as per the transistor datasheet

That C2335 was damaged before and I replaced it thinking that was the only part needed, then found the zener and resistor
 

AlbertHall

Joined Jun 4, 2014
9,882
Unless the diode was mechanically damaged, the problem is that it didn't blow up of its own accord - some other fault blew it up. It is likely that just replacing the diode will result in another blown diode.
 

Thread Starter

Gemmy101

Joined May 18, 2020
5
Unless the diode was mechanically damaged, the problem is that it didn't blow up of its own accord - some other fault blew it up. It is likely that just replacing the diode will result in another blown diode.
My assumptions scenario here .. something resulted in voltage peak .. hence the diode didn't handle it .. blown .. and the resistor two .. I think it was blown from the picture .. and that high voltage wave hit the C2335 and exploded it too ... and here the wave stop ..

so assuming we will give it a shot .. will it be safe to assume replace the C2335 with a new one .. same resistor and 7V zener ... will that work ? assuming no other faults in the PS ?
 

AlbertHall

Joined Jun 4, 2014
9,882
I think there are two of those big capacitors and, although it is difficult to see in the picture, it looks like the other one has that same brown mark in which case it may be glue securing the capacitors to the board rather than indicating damage.
 
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