On many of the driver boards I have all the resistors look like your top 3. I haven't had a system 3-7 game in year but clay had a good guide to troubleshoot these. I think most of that info is now on pinwiki. Also check Marks page for assembly drawing and schematics. http://pinball.flippers.info/system6resources.asp. arcarc.xmission.com should have them also.
Not sure if firepower.com is still around (never been able to reach it from work) but Richard was a great help to 3-7 owners when I got into the hobby 15 years ago.
I used to use LEONs test ROM to systematically troubleshoot these. I have been told there is a better version now. I think they say Marco made them. You put the ROM in the cpu and it will set the outputs of the PIA on off on off so you can work from the connectors back to the PIA to find any problems.
If you have any questions ping me and I can walk you through it from home one evening. i might be able to burn a test ROM for you if I have the correct size.
As for 2n6548, I don't remember that chip off hand, what is it used for ?