Synthesizer power distribution

[argonrepublic]

Pins 9, 10, 11 and 12 put out 12 Volts. Based on the datasheet for the HC139, the outputs can only be High on these pins in a group of 4. There is no option for them being all four "low". Based on this circuit, what is going to be required to provide collector voltage?

[Mooly]

Those transistors will be driven by a "logic" type output. To turn a transistor on those pins have to go to zero volts. That pulls base current through the E-B junction and whatever voltage is on the emitter (5V ?) then appears at the collector as well. But... the drive may be strobed and not simply static voltages.

You need a scope to check the clock (and for most fault finding really)

Faults usually fall into certain categories. You must check all the supplies. You must check any clock oscillators are running and you must check the status of any reset pins on any microprocessors.

You need to find a way into a fault if you are struggling. Is there a power on LED ? Does it light ? If not then look purely for the reason why that is.