This might be interesting to some.
I recieved this power supply with the issue of "not starting the computer"
The unit is a resonant topology with syncronious rectification plus two DC-DC converter on the secondary. All capacitors are NCC.
The owner attempted to repair the psu by replacing some caps... then putting the originals back.
When I powered up the unit for examination there was a stable 5V standby supply but after a few minutes a capacitor vented in the standby circuit. This power rail is generated by a TOP265EG monolithic device.
I replaced the exploded capacitor and started measuring voltages. After a few minutes the new capacitor blow up.
I started tracking the circuit and looked for more faulty parts. According to the TOP265EG datasheet the cap that blows up at C3 position is in the feedback bias for this standby circuit.
Then I noticed something wierd.
When powered there is 6V across this capacitor which is ok. But looking at the silkscreen the polarity is wrong! I couldn't believe it is reversed until I looked at a photo of an original unit for comparison.
So this means that the owner reassambled the unit back according to the silkscreening... and it fooled him too.
After installing another capacitor, this time reversed, there were no more explosions. I also replaced a fast diode just in case it might have been damaged.
Anyway, the original problem was caused by the faulty PS231 supervisor. The power-ok signal wasn't present when the unit was turned on. Replacing the ic solved the issue. I suppose this silkscreening mistake must have been known by Eneramx back then... after several failed units during testing.
I recieved this power supply with the issue of "not starting the computer"
The unit is a resonant topology with syncronious rectification plus two DC-DC converter on the secondary. All capacitors are NCC.
The owner attempted to repair the psu by replacing some caps... then putting the originals back.
When I powered up the unit for examination there was a stable 5V standby supply but after a few minutes a capacitor vented in the standby circuit. This power rail is generated by a TOP265EG monolithic device.
I replaced the exploded capacitor and started measuring voltages. After a few minutes the new capacitor blow up.
I started tracking the circuit and looked for more faulty parts. According to the TOP265EG datasheet the cap that blows up at C3 position is in the feedback bias for this standby circuit.
Then I noticed something wierd.
When powered there is 6V across this capacitor which is ok. But looking at the silkscreen the polarity is wrong! I couldn't believe it is reversed until I looked at a photo of an original unit for comparison.
So this means that the owner reassambled the unit back according to the silkscreening... and it fooled him too.
After installing another capacitor, this time reversed, there were no more explosions. I also replaced a fast diode just in case it might have been damaged.
Anyway, the original problem was caused by the faulty PS231 supervisor. The power-ok signal wasn't present when the unit was turned on. Replacing the ic solved the issue. I suppose this silkscreening mistake must have been known by Eneramx back then... after several failed units during testing.
Attached Files
Comment