armis2000
Well-known member
Geek question:
I was trying to get my servo board to work properly, but for some reason it was not activating the circuit past the 74HC174 flipflop. The Data input was toggling. The CLK input pulsing (altho my logic probe shows pulsing, but at logic high for most of the duty cycle).
Seeing that the data line was not strobed in any way (logic high when the blinders are supposed to be there, and low when not), I figured the 74HC174 was bad - socketed/new chip - same result. So, I tried simply jumpering the input of the FF to the output (pin 3 to pin 2, with the chip removed). The servo driver works now as expected.
Is there any reason why U4 is there at all? Maybe it was a throwback to being able to add servos to the lamp matrix? (CLK could be a row, and Data a column?)
Could someone validate the clock signal for me? If its bad, all I can think is the PIA has a bad line output going to the 74154.
I was trying to get my servo board to work properly, but for some reason it was not activating the circuit past the 74HC174 flipflop. The Data input was toggling. The CLK input pulsing (altho my logic probe shows pulsing, but at logic high for most of the duty cycle).
Seeing that the data line was not strobed in any way (logic high when the blinders are supposed to be there, and low when not), I figured the 74HC174 was bad - socketed/new chip - same result. So, I tried simply jumpering the input of the FF to the output (pin 3 to pin 2, with the chip removed). The servo driver works now as expected.
Is there any reason why U4 is there at all? Maybe it was a throwback to being able to add servos to the lamp matrix? (CLK could be a row, and Data a column?)
Could someone validate the clock signal for me? If its bad, all I can think is the PIA has a bad line output going to the 74154.
