Nov 302017

After reparing my Defender ( see this log: ) I noticed that the screen had some horizontal lines of different brightness.

At first I didn’t give much attention but then I decided to look at this issue deeper.

Moving the screen left and right with the monitor commands I noticed these defects:



Having the experience of a similar problem on my Burnin Rubber ( ), to me it was clear there was a video blanking problem

With the schematics in hand I found this circuit:

Signals from 7420@5C were good so I started probing the 7400@4B


All signals were good except that pin 10 was floating.

Looking at the above mentioned schematics, pin 10 is tied to the nearby pin 11!

I checked the board and found out that actually the pcb has no trace connected the 2 pins togheter!


No broken traces, it is actually simply not there!

I connected the two pins and…..


Game fixed!

Now I am wondering if my CPU board revision has a production error.

Searching on internet I haven’t found a similar problem therefore I would like to have a feedback from other owners of Defender if their pcbs has the trace or not.