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Battery charger killed a transistor

I would be grateful for your assistance with the Multipurpose Fast Battery Charger Mk2 which was featured in the June & July 2001 issues. I have built this project from a Jaycar kit and on switch-on I unfortunately had a short-circuit caused by a tiny piece of metal swarf trapped behind Q2. I have rectified this and all the tests mentioned in the article measure OK.

However the voltage across the output terminals remains at full (about 18V), irrespective of the position of switch S5. I have replaced IC1 but this has not improved matters.

(D. M., via email).

Almost certainly transistor Q1 has gone short circuit because it would have driven the short-circuited Q2. D2 may be OK but it would be wise to check that it is not also a short circuit.

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