I recently had the same problem with my DW423 and found what the fault was. Just next to the speed-control potentiometer there is a power transistor which is connected to both the live and neutral inputs to the control board (black rectangular component
about 1/4" square). I lifted it slightly and it fell off, so the adhesive that was securing it to the board had failed and the three terminal pins were fractured - presumably due to vibration over the years. I re-secured it using a spot of hot glue,
then soldered the terminals back together; now it is back to full working order. I cannot say thst this is the only cause of the problem, but consistent mass production does tend to produce consistent faults.
..Steven
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