24-01-2014, 09:12 AM
In a CD player I'm attempting to repair, there is a perfectly standard Bridge rectifier circuit, fed with 15vac. The resultant rectified & smoothed DC is split into +ve & -ve supplies, which are supposed to be +8.5v & -8.5v wrt earth. With both my Fluke 77 DMM and an analogue meter they meaure +19 & -19v wrt earth instead. The AC voltage is correct, and, unless I'm missing anything, there is earth continuity on the PCB, on which wire links between various tracks complete the circuit. To me, the off load DC should be ca. 21v, which, split into + & - rails would be about + & - 10.5v no load, so why am I reading 19v? Any suggestions as to the cause? I don't think a faulty rectifier would produce this fault, but would a missing earth link, for instance between the chassis tag and somewhere on the PCB cause it?
