You are on the right track. Connectors.
Did you repin A3J5?
Did you repin the sound board connector?
If so, are you confident that the pins are in the right locations?
Does the sound board make the correct sounds when performing the sound board test?
—
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

Pin 8 being low seems odd to me.
Will the sound board do what it is supposed to do when the diagnostic button on the sound board is pressed?
—
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

If a pin is grounded, connecting it to 5V won’t do anything other than send that additional 5V to ground.

You can ground a pin, but without cutting a trace or lifting a leg, there is no way to set a signal “high”.

Chris

Nope. One of the great revelations is that =most= digital circuitry works by pulling signals to ground. It’s easier. Hence the pervasive use of pull-up resistors. A signal is “defaulted” to 5V via a pull-up resistor but if connected devices provide a path to ground, that signal will always go low. One the path to ground is removed, the signal will again be pulled up to 5V.

A 7404 is an inverter.
You can ground the output of a 7404 or you can ground the input to force it to output logic low or logic high. But you can “inject” 5V attempting to drive a signal high without severing existing paths to ground.

Make sense?
—
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info