I have now mounted C6 and C7 to the board. After that I read the initial testing guide over at http://nwavguy.blogspot.se/2011/08/o2-details.html#initialdiytesting
Checked the power supply voltages with success (I think). According to the article the DMM should read 23-24V while mine showed 25V. Nothing got warm or hot as far as I could feel. Turned the power off and installed U2 and repeated the test above with the same results as should be. Then I moved on to the second test and this is where I hit some problems. I measured from the negative battery terminal of BT1 to pin #4 of the empty U4 socket and it should be close to -11.8V but my DMM showed -0.00V. Switching the probes gave me 25V reading. I then measured from the same negative BT1 to pin #8 of the same socket and this should give 11.8V but I got 25V again.
So right now I'm waiting for help, hoping that somebody will answer me in the O2 thread at diyaudio.com