Wednesday, January 13, 2010
Second PCB Bug
Mike Willegal had posted a question on applefritter.com awhile ago for someone to check/verify that pin 12 of the Address Decoder / 74154 was connected to ground. From the scans he was working with, he found that pin 12 was not grounded. I checked the board that came with the kit and could see visually, that pin 12 was grounded. At the time I assumed there was nothing wrong with the non-kit board I have, but I assumed wrong. Earlier this week I removed the DIP socket where the 74154 resides, because I wanted to check for solder-bridges under the DIP. I then placed multimeter leads (set to Ohms) from pin 12 to ground and verified that pin 12 is not connected to anything.
I resoldered a new DIP socket, and added a jumper from pin 12 to the ground side of the closest ceramic capacitor. Unfortunately, I am still picking up a 1+ volt signal on ground... more to come on this when I know more.
BTW, it appears at quick glance that the schematics omitted showing GND on each component.
Posted by John at 6:21 PM