1. The procedure to replace CALO rectifier (AC/DC converter) 1

2. – Check low voltage (LV) readings for the problematic power supply (PS) to be sure that it is not some sort of software glitch [see Slide #3 for xCAL readout crates PS / Slide #4 for phototubes PS or PS/SPD VFE] – If the problematic PS provides LV for detector photomultipliers: switch off Medium Voltage on the corresponding side of the corresponding detector (mandatory) together with Shift Leader exclude corresponding HV node from BigBrother tree (see Slide #5) exclude problematic PS from DCS tree (see Slide #6) so data taking can continue. Detector readout may stay in Global. – If the problematic PS provides LV for readout crate: ask Shift Leader to exclude corresponding detector from Global (in case of ECAL: together with TCALO). If it is not possible (e.g. the problem occurred in the middle of data taking), exclude corresponding readout crate from the Global hierarchy (instructions are here:) – Inform Shift Leader and descend downstairs. You will need a screwdriver. Preparatory Steps 2

3. 3 Checking LV readings (case of xCAL readout PS)

4. 4 Checking LV readings (case of phototube PS or PS/SPD VFE)

5. Exclusion of HV node from Big Brother 5

6. Exclusion of detector side from DCS tree 6

7. – Locations of rectifier units, protection relays and spare parts: see Slide #8 – Check white boxes with protection relays to see if corresponding relay has tripped [see Slide #9]. If boxes are locked, contact Eric Tomas or Laurent Roy. – If protection relay has tripped: Switch off corresponding rectifier (big green switch) Arm the relay again (push up its handle). If it is not possible, contact Eric Tomas (if he is not with you) – the problem is there. As soon as relay is armed, try to turn on the rectifier. If relays trips again, replace rectifier. – If protection relay is OK, check the status of corresponding rectifier [see Slides #10 and #11] The rectifier is OK, if the big green button is illuminated and status LED shines with green. Then the problem is elsewhere (99% probability). If rectifier is not OK: try to switch it off and then back on. If it will not help, replace rectifier – Replacement of rectifier [see Slide #11]: Obtain spare rectifier from PZ alcove [see Slide #8 and Slide #12] Switch off corresponding rectifier (big green button) Unscrew the unit and replace it with spare one In case of protection relay trip: arm the relay Switch on rectifier. If relay trips again, alarm CALO experts. Otherwise return to the Control Room and start recovery procedure. 7 Downstairs

8. 8

9. Protection Relays 9

10. Rack with Rectifiers 10

11. Rectifier Units 11

12. Spare Parts Location: PZ alcove, last floor (take stairs) 12

13. – In case of problematic PS for xCAL readout: Turn on the power supply via INFDAI Restart DAQ project for the corresponding side of the corresponding detector via Service+ (will take some time). Together with Shift Leader include corresponding detector itself (if it was excluded) or disabled power supply back into Global (if corresponding detector was not excluded) – In case of phototubes PS: Turn on the power supply via CALO_HV_top For affected detector part: – restart HV-control project via Service+ (will take some time). – initialize the system like after power cut, set Medium Voltage and apply HV-recipes (see presentation of Yuri Guz for details: https://indico.cern.ch/conferenceDisplay.py?confId=181183 ) https://indico.cern.ch/conferenceDisplay.py?confId=181183 Together with Shift Leader include back into LHCb_top and Big Brother trees the nodes which were excluded 13 Recovery