Wednesday, January 13, 2010

Second PCB Bug

Mike Willegal had posted a question on 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.

1 comment:

  1. Also verified that this connection exists, visually (on the top of the board) and electronically between pin socket and board ground pad. Thanks for making me aware of these potential headaches!