1. Chronology - I  Year 2007 + Jan. 2008: from time to time short circuits failures in chains supplying low voltage to C-W bases (either +6V or -6V, ~5 lines in total):  No more that 1-2 lines at the same time;  In all these cases problem caused by single malfunctioning C-W base with incorrectly soldered electrochemical capacitance;  End of Nov 2007: test batch of modified voltage delivery/control boxes is installed on ECAL (3 + 4). No problems observed for 2 months;  Middle of Feb. 2008: all voltage delivery/control boxes are modified;

2. Chronology - II  Middle of March 2008: after power cut one short-circuited line appears on A-side. After another switching on/off MARATON supply another short-circuit is observed;  9 April 2008: 5(!) short-circuited power lines on C-side. Reasons and conditions: UNKNOWN (community keeps silence); All ‘after-modification’ cases show the same pattern:  short-circuit is in +6V chains;  short-circuit is due to not recovered fuse in the voltage delivery / control box;  short-circuit happens after (? incorrectly preformed ?) low voltage power supply (MARATON) shut-down;

3. Brief comments on modification Goal: stabilization and increase of low voltage on ECAL C-W bases Change: new type of (resettable) fuse in LV chains. Fuses of old type have large dispersion in internal resistance R, which, together with large value of R itself, resulted in noticeable voltage drop on it. As a consequence, there is an undesirable decrease of LV on the C-W bases. The value of the effect depends also on the load of the line (i.e. number of C-W bases served by it).

4. Fuse data sheet

5. Laboratory studies: burn tests 1.Operational conditions check: at U=8V no trip up to I=0.4A; Internal resistance value R is 1.6 Ohm and does not change 2.Trips at “soft” conditions: U=8V, I varies from 0.5 up to 3A: 1.After the first trip at 0.5A R increases up to 2.3 Ohm 2.Next trips: fuse recovers to the value R=2.3 Ohm; recovery time is ~10min 3.Trips at “hard” conditions: 1.high U=24V, I varies from 3 to 5A. Fuse recovers to the value R=2.3 Ohm; recovery time increases to 60 min; 2.Data sheet max U=30V. R increase to 3.9 Ohm, but fuse is still operational 3.I=10A and U=60V. Fuse recovers to the value R=3.9Ohm; it is still operational Even at the abnormal current/voltage conditions, which can not be achieved in the ECAL system, it was not possible to reproduce an effect of non-recovery in the lab

6. Conclusions / proposals / requests …  2 versions of what is happening:  small fraction of fuses is defective. As soon as all of them will malfunction and replaced, the problem will disappear;  abnormally high currents sometimes appear at the moments of ECAL LV power sources shut-down for reasons unknown. These reasons must be understood;  Therefore our proposal is:  avoid unnecessary switching ON/OFF MARATON LV;  if there is a need to switch it OFF (e.g. for preshower people) – contact us first, we will check current ECAL conditions;  each turning ON/OFF of MARATON should be mentioned in CALO logbook together with the status of ECAL HV Agilent power supply;  request to ECS group: is that possible to record automatically all moments when MARATONS and also AGILENTs channels are turned ON/OFF?

7. Conclusions / proposals / requests (cont) …  Correct procedure to switch OFF the ECAL:  Set zero HV codes on ECAL PMs;  Set zero MV on Agilent power supply;  Switch OFF LV (MARATON). All 4 dedicated channels of MARATON power supply must be turned OFF at once. DO NOT TURN OFF single channel, it can cause MARATON supply failure;