No CV output / No Output at DAC0800

[5chn3]

Hi, I've built a P&P incl. IC set from Thonk. Everything seems to work fine, except the CV output. I already checked the circuit from the jack backwards. I found out that the DAC is not putting out any voltage at all, where it is supposed to. I measured all pins on the DAC while a slow LFO was doing the clock with the following result: 1 and 2 have 0 V, (for 1 I don't even understand what it's there for), 2 should actually output something, 3 has -12 V as expected, 4 again has 0 volts, should also output something, the input pins all behave the same. I measure 10.7 V on all of them when an input comes in, but the multimeter always peaks above 16V for a fraction of a second before it stays at 10.7 for a while and then goes back to 0. Not sure what that means? Pin 13 has the expected +12V, pin 14 has -5V, pin 15 has 0V and pin 16 has -10.5V. What the latter 3 do exactly, I have not yet understood. I have borrowed a replacement DAC from a friend, same behaviour - so would be quite a coincidence if both where broken. Or is there something wrong happening at an earlier stage which breaks the DAC as soon as it's switched on? Would be great to get some hints what might be the issue here and where to look at next. Thanks a lot <3