PT losing sync...

[Raven]

System : PT HD3 + 192 I/O with DA card + Sync I/O.
Connection : SMPTE from 24 track (2" Studer tape) is fed to SMPTE In of Sync I/O. Word Clock out of Sync I/O is given to WC in of the 192 I/O.
Session Setup : Session is at 48kHz. Clock source - Internal. Positional Ref - LTC
Hardware setup - 192 is set to Clock source - Word Clock 48kHz
When running a session in sync with the tape, by putting PT 'online', there is a drift. This does not happen all the time.. e.g PT is recording two tracks and everything is in sync and is all fine. If we go for a re-take, the PT is running slightly off-sync with the tape!! Sometimes, you play back the same place and it is in sync again!!!!
What can be wrong? Any suggestions? This is a prestigious client.
Thanks

[Robotnik]

You're getting drift cause your 2" is the master...it should be code-only master (i.e. used as positional reference...SMPTE...for Pro Tools).
You need to invest in a synchronizer (such as a Time-Line MicroLynx) and a blackburst generator.

Clock Reference:
Blackburst to both a MicroLynx and a Sync I/O.
MicroLynx resolves to blackburst and in turn resolves the servo of the 2" machine.
Sync I/O also resolves PT to blackburst.

Positional Reference:
Timecode out of track 24 of the 2" into the Sync I/O.
Put PT online (command+j), press play on the 2" and PT receives the SMPTE trigger point and follows along.