Peale
Active member
Not mine, nor do I have access to it.
He replaced 8E and its still doing it. I told him to check out the other chips that relate to this, but he's having trouble reading the schematic. Any ideas?
So, I used the multimeter to measure the pins on the 74LS chip responsible for joystick movements.
I found the pin layout (if that's the right term) for the 74LS367 chip responsible for up-down-left-right. I also found this great site (http://lawnmowerman.rotheblog.com/logicprobe.html) that basically lays out how to measure it.
I used my schematic and found that pins 14 to 13 are responsible for Down on the 74LS chip at location 8E. I also learned pins 10 and 9 are responsible for Up. Basically, I measured the voltage between pins 14 and 13 and found they were always at 4 volts (I had my multimeter set to AC10V). Pins 10 and 9, 6 and 7, and 4 and 5 were 0. I then measured pins 10 and 9 while the up switch was depressed and it read 4 volts. When turned off, it went back to 0. So pins 14 to 13 are always on. What does that mean? Bad 74LS chip? I also learned R45 and C20 are the resistor and capacitor responsible for down, respectively (220 ohm, .1 microfarad). I have no clue if the Res. and Cap. are contributing to the problem.
He replaced 8E and its still doing it. I told him to check out the other chips that relate to this, but he's having trouble reading the schematic. Any ideas?

