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**R_J** · 11-10-2021, 12:59 PM

107vac is likely that they have 3 phase power supplying the building and they use one phase to supply the board, this is normal.
Locate the source for the -15v, trace the -15volt point back, the ac for this circuit is likely supplied from the transformer and then through a diode or bridge to give a negative voltage.

11-10-2021, 12:59 PM	#18
R_J Badcaps Veteran Join Date: Jun 2012 City & State: ☻ My Country: Canada I'm a: Professional Tech Posts: 8,146	Re: Motor control board repair 107vac is likely that they have 3 phase power supplying the building and they use one phase to supply the board, this is normal. Locate the source for the -15v, trace the -15volt point back, the ac for this circuit is likely supplied from the transformer and then through a diode or bridge to give a negative voltage.