Re: Short circuit in buck converter QMX
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Hi Kees, all ? One thing that may have made this a little confusing for some is that the QMX schematic (marked up in red) is not correct. The short is between the large Drain Tab of Q103 and the Drain of Q104 (which also happens to be connected to the Gate of Q105 and to the Gate?of Q103, the D101 Diode, and R104.? ?
Just to be completely clear, to avoid making the confusion deeper: Jacques original marked up diagram is incorrect. The QMX schematic is totally completely correct. But the red mark-up is wrong. It should be as per the attachment to this message. I also marked D (Drain), S (Source) and G (Gate) in Blue. ?
Heating up the Drain Tab of Q103 and pushing the Drain?Tab a little toward the edge of the board (to eliminate the short or reduce the short potential) should not hurt the two Q3 leads any.
This is could be one of those rare QMX "sleeper" problems depending how far the Drain points are apart. Definitely worth a quick check with a magnifier.?
FYI all assembled QMX that are produced here, I am now checking them for this short before powering up. I have not found any yet. So I think it is not all that common; but definitely worth checking!
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