Electronics > Repair

DSO-X 3024A Power Supply defect

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rernexy:
Finally got around to dismantling my msox3054a after 8 or 9 years. Partly because of a high pitch hissing sound that always seemed to be present, and it's waaaaay out of warranty so now idgaf.

But lo and behold look what I've found on the power supply, the blackening around the 22K resistors under the big arse 420V cap.
The little black chunk to the left is what flaked away when I gently prodded between the leftmost 2 22K resistors, it's exposed a track.
Also you can see that on the underside of the shield it is starting to discolour/blacken in line with either the resistors or that mosfet (don't know).

Maybe time to throw the parts-cannon at it for pre-emptive maintenance.

Jwalling:
In years past, HP/Agilent would issue service notes on things like this.

rolkinas:
Hi, don't forget to check capacitance of 420V cap. It probably is semi-dry.
I am thinking about mounting something like power resistor on psu shield-heatsink in place of smd. something like ROX5SJ91K from Digikey.
Leaving these baking 22K where they are now is asking for trouble.

rernexy:
Decided to desolder the 22K resistors.
They were hiding more blackening/carbonising/burning of the PCB. Pretty sure that wasn't my desoldering.

rernexy:
Different view of the pads (continuing previous post).
Shining a light from the opposite side, after removing the 420V cap, you can see cracks more easily on the inside of the resistor solder pads.
There is a faint crack at the upper right resistor, bottom pad.

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