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Sunday 10 December 2017 at 00:45
To add to this --
R10 can be anything from about 300 ohms to 680 ohms. Higher value = less heat but also more of a chance of transformer load current affecting the voltage (as if it really matters that much). Lower value = more heat but less of a chance of transformer load affecting the voltage. ...
Source: http://pinside.com/pinball/forum/topic/gottlieb-system-80-power-board#post-4115789