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January 18, 2024

Ryobi and Skil Charger Repairs After Overvoltage Condition

Filed under: Uncategorized — admin @ 6:39 pm

Recent repairs for a friend. 7 separate devices (6 tool battery chargers -5 Ryobi units and one Skil charger) and an oven controller were brought to me after having failed due to an extreme overvoltage condition in an off-grid cabin.

All of the chargers are fixed now, after a significant number of fairly straightforward component replacements.

In this case, the “defensive”, sacrificial components in the circuit designs -mainly varistors, current fuses, and solid state thermal fuses – sort of did what they were designed to do and blew into open or shorted failure as designed, but not quickly enough to save a significant set of early stage power supply components. There were some spectacularly blown electrolytic capacitors and varistors, a fried transformer, and some failed switching ICs, but everything past the power supply stages of the circuits turned out to be OK.

Repaired Ryobi Fast Chargers

The total blown parts list from this single incident is remarkable:

9 blown capacitors -including some big ones

5 varistors

2 switching ICs (TOP250EN series)

5 fuses

one thermal breaker on a charger transformer

a really fried transformer on the oven controller board

All 6 chargers are fixed and working now. Still waiting for a replacement transformer for the oven controller.

visibly blown capacitor and varistor
Skil charger: this one had an open circuit thermal fuse adjacent to the primary winding that I replaced.
More blown capacitors -Ryobi fast charger
Ryobi standard speed charger adapter. These can be cracked open with e.g. a wide chisel and a hammer. Note the blown capacitor and blown varistor beside it.
Ryobi fast chargers, working OK post repair.

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