[Dr_C2]

REPAIR RESULTS
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Repair results on the above 14 faulty decoders:

Step 1:
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All diodes were found to function correctly - non required replacement.

Step 2:
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On removing the two MOSFETs and replacing onIy the n-channel MOSFET, 11 decoders became controllable.

The 3 that didn’t function were investigated and corrected. One had a failed on-board ferrite bead inductor. One had a failed npn transistor (preventing motor turning on). The third had a damaged interconnect track. 

Step 3:
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On replacing the p-channel MOSFET again, 11 decoders became controllable in terms of both motor and brake. All three were found to have failed brake enable npn transistors. One failed open circuit so simply the brake would not function. Replacing the npn fixed this problem. The other two had failed as short circuits so the brakes were permanently applied - even when the throttle was applied too. In each the case the npn was replaced and a pair of replacement replacement MOSFETs were fitted (as this brake-on condition can further damage the MOSFETs).

OUTCOMES
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14 fully functioning and upgraded C8515 decoders. No write-offs :)

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