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Entry  Thu Aug 6 23:29:47 2009, Jenne, Update, PSL, Ref cav reflection PD is funky 
    Reply  Fri Aug 7 00:10:14 2009, rana, Update, PSL, Ref cav reflection PD is funky 
       Reply  Fri Aug 7 17:05:34 2009, Jenne, Update, PSL, Ref cav reflection PD is funky 
Message ID: 1860     Entry time: Fri Aug 7 17:05:34 2009     In reply to: 1851
Author: Jenne 
Type: Update 
Category: PSL 
Subject: Ref cav reflection PD is funky 


we have a tester cable, but you don't want it. Instead the problem is probably at the cross-connect. The D-cable goes to a cross-connect and you can probe there with a voltmeter. If the signal is good there, trace it to the ADC. Also trend for several years to see when this happened - Yoichi may know the history better.

Also, we still need to complete the FSS RFPD task list from last year.


 [Jenne, Ben]

I called in the reinforcements today.  Ben came over and we looked all around at all of the cross-connects and cables relating to the FSS.  Everything looks pretty much okey-dokey, except that we still weren't getting signal in the DataViewer channels.  Finally we looked at the psl.db file, which indicates that the C1:PSL-FSS_RFPDDC channel looks at channel 21 of the ADC cross connect thing.  We followed the cable which was plugged into this, and it led to a cable which was disconnected, but laying right next to the Ref Cav refl PD.  We plugged this into the DC out SMA connection of the photodiode (which had not been connected to anything), and suddenly everything was mostly golden again in dataviewer land.  RFPDDC_F now has a signal, but RFPDDC is still flat. 


Even though this seems to be working now, it's still not perfect.  Rob suggested that instead of having this SMA cable going from the photodiode's DC out, we should take the signal from the ribbon cable.  So I'm going to figure out which pin of the D-connector is the DC out, and take that from the cross connect to the ADC cross connect.  This will help avoid some persnickity ground loops. 

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