So I thought the unit was dead because LED light wasn’t even turning ON. My first suspect is the power switch because this switch is sticky, so I thought that’s where I would start… but doing simple resistance check on this DPDT switch shows it’s working properly. (The spring may be a little weak, but the contacts are good.) I powered the unit, and yup, LED does not light up… but doing random spot checks on the two PCBs (touching my positive probe to the various body of the transistors) shows that I’m getting some voltages. So the unit is not “dead DEAD” but it’s getting power to the boards. But why does the LED not lighting up?
I found a scanned copy of the user and service manual for the 8012B and while there is no schematic, there’s a good block diagram and theory of operation. On one of the section, labeled Power Supply, it shows there’s a couple of Test Points on the board. So I should measure +17Volts and -17Volts on these. Powering up the unit, I discovered that I don’t have any +17Volts. AHA! That could be a problem… and maybe that Power LED is connected on that Positive Rail and that’s why it’s not lighting up… So most probably, the Positive +17V Power Supply is where the problem lies.
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