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Due to an error on my part I thought I had blown the final transistor (Q7). I replaced it twice and it still did not work. I then found that D19, 1N4753 had shorted. Not wanting to go thru that again I installed a polyfuse in series with D16. I lifted the diode cathode lead from the board and put the fuse in series with D16 cathode and the original location of D16 cathaode on the printed circuit board. I obtained this part from Jamco Electronics part nr 199902CC. This will pass 900 ma and trip at 1.8A.