[robb]

hello,

i am trying to repair a fault with an user interface circuit (UIC) board and
control board out of an old 1987's computerized programmable Pfaff sewing
machine (made in Western Germany).

a for fun project for me , a challenge

programming consists of storing values in memory locations using keys ( +/-
buttons) on UIC board

PROBLEM : a group of 3 (+/-) *momentary switch* buttons on UIC board used
to change memory values do not make any changes when pressed.

the UIC board has a VFD output display (16 chars) and 12 input buttons and 5
indicator LEDs. All but 3 of the buttons register presses correctly. the 3
broken buttons seem to be individually ok as i get continuity changes when i
test with multimeter and push buttons.

this UIC board is connected to the control board via 12 conductor ribbon ???

I am not sure what kind of things to do to isolate trouble ........

i have dome visual inspection of solder joints and components with no
obvious issues.

How would the VFD display values , LED indicatiors and inputing buttons be
managed through a 12 conductor ribbon ??? in 1980's style ?? how to trace ot
monitor value changes.

Any troubleshooting or tracing ideas advice would br greatly appreciated.

thanks,
rob