09 March 2009 Shutdown Calo meeting CERN E.Gushchin (INR,Moscow)

Status PS/SPD of LED tuning

Status of tuning on A-side.

Some problems

Results of tuning

To do

09 March 2009 Shutdown Calo meeting CERN E.Gushchin (INR,Moscow)

Status on A-side

PS:• After first tuning there were two things remaining to do:

– One “hot” LED– There were no data from FEB6

Status:• “hot” LED – was not a problem of unstable resistor, just tuning (good news!)• After FEB6 show data it was tuned, some LED may be still too low.

SPD:• It was tuned without presenter in 2008. Two problems arrived:

– two LEDs (in SPD6-2 and SPD8-2 bias lines) seem dead with shortcut. This brought all LED in group lost regulation. – LEDs to be cut off.

– Regrouping of DCS lines– Bad news: During last week one more LED died! Again in the same group of SPD6-2 bias line. This is a very

first observation during all the time after LED system installed. Investigation is going on, few hypothesizes…

Status:• 2 LEDs are located and cut• Regrouping was effective. Only few (<10) LEDs need to be tuned.

09 March 2009 Shutdown Calo meeting CERN E.Gushchin (INR,Moscow)

Some problems

Dead LEDTwo hypothesizes:

1. Accidental death (aging, mechanical stress of LED after machining)

2. Electrical damage (overload, discharge, unstable contact)

If it is p.1 or instability of contacts, it is difficult to identify but it should go away with time.

If it is problem of regime of operation, it needs urgent investigation.

Ways of investigation:1. Check of electrical circuit on detector.

2. Investigate some extreme regime “on table”

One idea came: LED bias at 4000 counts (DCS) sends -5.2V on SPD6-2 line, this exceeds the absolute rating value of reverse bias (5V). Therefore the “default” DCS setting is changed now to 3000 counts, which is safe both for PMT and for LED.

Now I study in details how to kill LED on table: overvoltage, transient effect.

09 March 2009 Shutdown Calo meeting CERN E.Gushchin (INR,Moscow)

PS-A delays

09 March 2009 Shutdown Calo meeting CERN E.Gushchin (INR,Moscow)

PS-C delays

09 March 2009 Shutdown Calo meeting CERN E.Gushchin (INR,Moscow)

Plans for this week

• To have an access to SPD-A site (from today evening) in order – to tune remaining LEDs

– To fix dead LED

– To check SPD6-2 line and circuitry

• In case of access to PS to tune few more low LED.

• To continue monitoring of PS/SPD

• To study urgently dead LED case.