I’m trying to diagnose a few bad buttons on a metal-case Ensoniq ESQ-1 (the stop button, Bank Select button #4, and soft button #4) that suddenly stopped working.
I see they all share a trace on the panel board, and when I measure voltage on that trace to ground it reads around .2 volts and then slowly drops in voltage as I watch. Measuring voltage elsewhere on board shows 4.7, 3.7v, or 0 but nothing else shows low voltage with a slow drop like that.
Does anyone know what voltage I should be reading at these buttons?
Got a really helpful email reply back from Rainer Buchty so I want to share for the next person:
The row lines are input lines, so technically they should exhibit the
pullup voltage in inactive state and fall down to zero (or at least
logical low) with a pressed button.
However, the latter you wouldn’t really be seeing with a voltmeter, but
rather an oscilloscope.
Assuming that no button is pressed, seemingly something is bringing that
input down that shouldn’t.
I disconnected the panel board completely and checked voltage directly at the row 7 pin on the 65003 display board chip and saw the same .2 volts, so it does look like that IC is bad. Off to find a replacement!