QJE PS3010 - bad EMI/RFI bypass ceramic cap on secondary side

[japlytic]

This unit was exhibiting a residual load on the LCD screen beforehand, and later on, developed a short between the +ve output terminal and the chassis and therefore causing current limiting to engage if I connected the output to a grounded device.
I found it was not caused by a short between the output rectifier and the chassis; it was caused by a shorted 0.01uF ceramic capacitor (for EMI/RFI filtering) between the +ve output terminal and the chassis.
After replacing this capacitor was replaced with a 1kV ceramic unit, the load displayed 0.0A when the output terminals were not loaded, and when I tested this unit with a 15 ohm load at 12V (0.75A current draw), there was little error.

[ben7]

Re: QJE PS3010 - bad EMI/RFI bypass ceramic cap on secondary side

This unit was exhibiting a residual load on the LCD screen beforehand, and later on, developed a short between the +ve output terminal and the chassis and therefore causing current limiting to engage if I connected the output to a grounded device.
I found it was not caused by a short between the output rectifier and the chassis; it was caused by a shorted 0.01uF ceramic capacitor (for EMI/RFI filtering) between the +ve output terminal and the chassis.
After replacing this capacitor was replaced with a 1kV ceramic unit, the load displayed 0.0A when the output terminals were not loaded, and when I tested this unit with a 15 ohm load at 12V (0.75A current draw), there was little error.

Was the capacitor a regular ceramic capacitor, or a supposedly safety rated one? Just curious.

[japlytic]

Re: QJE PS3010 - bad EMI/RFI bypass ceramic cap on secondary side

Was the capacitor a regular ceramic capacitor, or a supposedly safety rated one? Just curious.

The failed capacitor was a regular low voltage ceramic unit.

[electricboyo]

Re: QJE PS3010 - bad EMI/RFI bypass ceramic cap on secondary side

It would be quite useful if you could post a picture of the board and of the capacitor.

I have recently seen several ceramic capacitors that became leaky. Not necessarily a dead short, but a low enough resistance to cause malfunctions.

Unlike electrolytic capacitors, ceramic capacitors rarely show any physical signs of damage.

[Th3_uN1Qu3]

Re: QJE PS3010 - bad EMI/RFI bypass ceramic cap on secondary side

The SMD ones usually do, however they're small so still hard to spot. Also on most low-quality leaded disc types, they burn noticeably when they short. But indeed, not all of them do it.