Problem SBC V2 no puls on pin 20 Z80

[rbruinsma <rbma...@gmail.com>]

I have a little problem to get my SBC to run. I have read a lot of posts on this form and checked the most things that were suggested in these posts.
The only thing that I can find that is wrong on board is that I have no pulse on pin 20 of the Z80 IC. (tested with a logic probe)

What does that mean? What could I check next?

What I have checked so far:
- pulse on pin 6 of the cpu and pin 16 on the 16550 
- VCC on all IC's
- solder work, re-tipped a few
- reburned my rom a few times, no errors and I use the ROMWBW
- tried two different max232: ADM232A and MAXIM 232CPE