[Federico, Matteo, Eleonora]

In the past few days we had many troubles with our DACs. Several channels were not working and moreover the issue seemed somehow "non stationary": some channels stopped working, than worked again, etc..

After we veryfied that the connections and the hardware have no evident problems, we decided to change the old DAC board with a new one. This seems to have fixed the problem. We also installed the cable to connect the second DAC board to the timing box and test the signal chain. We had to deal with several issues:

1) Dsub to BNC board installed in the cleanroom had a strange behaviour. We found some jumpers were missing inside and we soldered them (we could't find proper jumpers in the elec-shop). Now it is OK.

2) The AI board has only 8 channels (instead on 16)  but only channels 2-3-4 seem to work fine. Channel 1 has a large offset and the signal is very much attenuated, channels 5-6-7-8 show crazy things.

3) In general both the dsub to BNC boards show an oscillation at about 1 MHz, with amplitude of volts, when the output is probed with a long cable. This issue was also observed in KAGRA. (Entry #6266 of Klog). According to our expert electronician this is due to the cable impedence which induces an auto-oscillation of the last op-amp. This could have been solved by inserting a resistence before the output. Note that we are currently sending such dirty signals to our coil-drivers. Hopefully the oscillation frequency is so high that they don't really care? Note that most but not all the channels show this behaviour.