Omron power supply 6.5A 24vdc. Model number S8JX-15024CD. Used in industrial field.
History:
there was a direct short between V+ and V-, the short was from the wiring on a +24v distribution terminal block. It was used in a biscuit factory.
Since then, power supply was showing 24vdc without load but it was dropping to 17-16v as soon as it was hooked to a load.
I decided to repair the PS and use it on my bench. Inspected power supply, hooked it to 220vac, and nothing visually obvious, output green led was on, but a tic tic tic sound was coming from pwm controller. As if it was entering over current or overload protection.
Didn't noticed any obvious short on dc output.
Unfortunately I didn't had time to push further investigation and the power supply just exploded because of a small staple that fly directly into the pcb. This is dumb and dangerous I know
Damage:
-KA7552 PWM controller exploded
-A diode (D5) sitting between GND and the controlled power mosfet gate, not sure witch type, labeled 4 79 was full shorted (not burned).
-Power mosfet 2Sk3875 exploded
-Fuse 5A 240VAC blown
-A couple of resistors on the path looked burned.
What I did:
-Restored all blown components with original one except power Mosfet.
-Replaced any suspicious resistors
-Checked all diodes and they are fine except the one that shorted.
-Removed the shorted D5 diode.
-Checked for any burned traces, all ok.
-Checked the AC stage with the bridge rectifier and the main 400v Cap.
-Checked the (regulated ?) 24vdc stage (after transformer)
There is no more short.
My questions:
1)
I have a power Mosfet STW15NK90Z it looks pretty same than original 2Sk3875. Main specs look very close.
Any advice/toughts if it is suitable? Am I missing other important details?
Here is both datasheet links:
Replacement : http://www.st.com/resource/en/datasheet/stw15nk90z.pdf
Original : http://pdf.datasheetcatalog.com/datasheets/105/499735_DS.pdf
2)
D5, the shorted diode between gnd and power mosfet's gate has this marking 4 79. "4" on the radial orientation and "7" followed by "9" on the axial.
I googled 479, 4-79 and 79 and found BA479 PIN diode and schottky barrier diode 30v 1.5a. But not sure about the results accuracy.
The output controller is rated at +/-1.5A. And vgs on the replacement Mosfet is 30v.
What suitable diode can I fit?
Also, the replacement power mosfet datasheet states that it already has an integrated Gate-Source protection zener diode and no need of external protection component.
Am I lucky on this one and could forget about replacing the diode?
Please find the following pictures:
-A partial circuit draft (hope no mistake there!)
-D5 shorted diode pictures
-PCB pictures
Thanks in advance
History:
there was a direct short between V+ and V-, the short was from the wiring on a +24v distribution terminal block. It was used in a biscuit factory.
Since then, power supply was showing 24vdc without load but it was dropping to 17-16v as soon as it was hooked to a load.
I decided to repair the PS and use it on my bench. Inspected power supply, hooked it to 220vac, and nothing visually obvious, output green led was on, but a tic tic tic sound was coming from pwm controller. As if it was entering over current or overload protection.
Didn't noticed any obvious short on dc output.
Unfortunately I didn't had time to push further investigation and the power supply just exploded because of a small staple that fly directly into the pcb. This is dumb and dangerous I know
Damage:
-KA7552 PWM controller exploded
-A diode (D5) sitting between GND and the controlled power mosfet gate, not sure witch type, labeled 4 79 was full shorted (not burned).
-Power mosfet 2Sk3875 exploded
-Fuse 5A 240VAC blown
-A couple of resistors on the path looked burned.
What I did:
-Restored all blown components with original one except power Mosfet.
-Replaced any suspicious resistors
-Checked all diodes and they are fine except the one that shorted.
-Removed the shorted D5 diode.
-Checked for any burned traces, all ok.
-Checked the AC stage with the bridge rectifier and the main 400v Cap.
-Checked the (regulated ?) 24vdc stage (after transformer)
There is no more short.
My questions:
1)
I have a power Mosfet STW15NK90Z it looks pretty same than original 2Sk3875. Main specs look very close.
Any advice/toughts if it is suitable? Am I missing other important details?
Here is both datasheet links:
Replacement : http://www.st.com/resource/en/datasheet/stw15nk90z.pdf
Original : http://pdf.datasheetcatalog.com/datasheets/105/499735_DS.pdf
2)
D5, the shorted diode between gnd and power mosfet's gate has this marking 4 79. "4" on the radial orientation and "7" followed by "9" on the axial.
I googled 479, 4-79 and 79 and found BA479 PIN diode and schottky barrier diode 30v 1.5a. But not sure about the results accuracy.
The output controller is rated at +/-1.5A. And vgs on the replacement Mosfet is 30v.
What suitable diode can I fit?
Also, the replacement power mosfet datasheet states that it already has an integrated Gate-Source protection zener diode and no need of external protection component.
Am I lucky on this one and could forget about replacing the diode?
Please find the following pictures:
-A partial circuit draft (hope no mistake there!)
-D5 shorted diode pictures
-PCB pictures
Thanks in advance
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