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LAr at Point 1 : Power supplies

LVPS supplies electronics to a Front End crate 2*16 in Barrel, 2*13 in Endcaps LVPS takes 280V (from USA15) and makes +-4, 6,

+-7, 11V up to 180A (total ~3kW) Modular : N module contributing to current. N+1

modules available for each voltage (27 modules/PS)

Radiation tolerant, Redundant, very tightly packed Long story of failing manufacturing going back to year

2003 Recurring problems lead to frequent exchanges during

installation phase in pit 2006: Task force (ATLAS, BNL, expert consultants)

identified problems Design issues Fabrication issues Proposed a complete reworking of the parts 2007 Refurbishment: components, connectors,

screws…. (~50 modifications/module) During operation 2008 all LVPS worked OK but

2 in redundant mode 2 identified a “new” failure possibility not

addressed in 2007 Campaign

L.Hervas 1

2008-09 : new retrofitting campaign (all 58 LVPS from point 1 to US and back)2008-09 : new retrofitting campaign (all 58 LVPS from point 1 to US and back)

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LAr at Point 1 : LVPS To come

One [known] unsolved issue (Capacitor damage “C26”) we could not find a better replacement

58 LVPS in operation since April 09, no failures, no redundant mode If one “C26” fails, that voltage goes into redundant mode. LVPS can operate OK. Would need to have a new failure in one of the other ~4 modules of that

voltage. Conclusion: we have fixed all we could LVPS in good shape, redundancy should work

Medium term: producing a new set of LVPS 2 Vendors contacted Phase 1: Single voltages modules of correct size, done OK Currently making full prototypes (delivery ~September09) Choice of vendor End 2009 Production 1st half 2010

Prove reliability of series off detector (?) Installation when access permits

L.Hervas 2

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LAr at Point 1 : OTx

OTx is the optical transmitter sending off the serialized data of one FEB to the ROD.

Mezzanine : little circuit + Laser emitter (VCSEL) coupling onto fiber with ST connector

1 OTx / FEB (Tiles has 2!) Reliable devices were difficult to obtain in 2005 at the

time of FEB production After QC and other improvements devices were

acceptable Extra steps of QC … Problems seemed solved

No failures during ~1.5 years

L.Hervas 3

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LAr at Point 1 : OTx

L.Hervas 4

In 2008 operation ~8 devices failed Abruptly Not correlated to anything obvious (B, power on,

humidity) All replaced during shutdown

In 2009 they keep failing, ~1/week (out of the 1600) By now (since detector closed in May) 5 dead Happen anywhere (now 4 Front, 1 Middle) Always : VCSEL is the element failing

Task force analyzing the causes and preparing actions No root cause yet Also failed efforts to estimate the size of problem ESD damage at the time of fabrication is main suspect Expect some results from FA experts starting now Preparing backup device

Other VCSEL, similar circuit, similar mezzanine, produced under best conditions

Double VCSEL, but would need two fibers. Difficult installation (eg. in EC chains)

Replacing all OTx’s is a BIG operation Unclear when it could take place

Effects can be mitigated with L1 Trigger readout