Tracing down a short circuit Williams 11a mpu Board.

[GrizzlyNate]

I have a F-14 Tomcat I have redone but having issues with a board that has been reworked. I have found an issue but having trouble finding a schematics on line that I am not having to scroll around to trace the issue I have found. So first when I go to boot the MPU I get the solid 5V light and have tested voltages and all are in range from the power supply and what is being sent to the MPU board. What I have discovered is I have a short doing a diode test on the u54, u51, u42, u41, u38, and u10 the the short does not continue to u9. I know there should not be a short as I have another board to compare the chips to. If I am reading the schematics correctly this is the data bus line so I need to figure out what is causing the short. Do the chips go in order and if U10 is the first with the short it is the bad chip or one to look at? I also know that the U25 chip reads into this line as well. I am still so new at this all but trying to read and understand. I know that cause of the short the mpu wont boot so once I fix this I hope it boots and can start to work on the next part. Any help or advice is greatly apricated and any questions that gives me better understanding or help is greatly apricated.

Thanks,
Nate

 

[russdx1]

If it’s a bus many chips could be connected in parallel to it. Try removing the first chip one that probably drives the bus?

 

[GrizzlyNate]

If it’s a bus many chips could be connected in parallel to it. Try removing the first chip one that probably drives the bus?

It was in the data line. Turns out if I remove the u27 eprom the short goes away so I know it’s that chip. The next thing is trying to get the t48 to write on the eproms i have as i keep getting a failure.