SDG #259 Metallised Paper Capacitors still causing damage... Bosch GEX 150 Turbo

Metallised paper capacitors, the notorious RIFA style parts that crack, absorb moisture and eventually vent in a cloud of smoke, turn up in far more than just vintage test gear. Here they appear inside a Bosch GEX 150 Turbo random orbital sander, where the failure produced the familiar acrid smell and blown open casing rather than any dramatic destruction of the tool itself.

The repair starts with getting into the sander’s housing, which involves working around the dust extraction path and the speed control electronics tucked into the handle. Once exposed, the failed part is identified as a mains rated suppression capacitor sitting across the supply, paired with the tool’s soft start and speed control circuitry. That distinction matters: X class capacitors across live and neutral are there for EMI suppression, so a failed unit does not usually stop the tool working, it just makes it noisy electrically and smells appalling. It is also a safety issue if the wrong replacement is fitted, so a correctly rated modern film capacitor is the only sensible substitute.

The wider takeaway for anyone with older power tools, oscilloscopes or bench supplies is that these paper capacitors are a scheduled failure, not a random one. If a tool of this era is being opened for brush replacement or a bearing service, it is worth pre emptively swapping any metallised paper suppression capacitors while the case is already apart. Reassembly and a running test confirm the sander is back to normal with no lingering smell or tripping issues.