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I'll add my two cents on this topic. We recently had a problem with our 733 that it wouldn't switch over to the diffusion pump within the 30-minute timespan when rough pumping, but would usually get it after restarting with the key. The problem actually turned out to be one of the thin-windows on the gas-flow spectrometer counters. Counter window had a defect was leaking just enough P10 into the chamber to make the vacuum poor. We replaced the counter with one with a good window and it went back to pumping down like a champ.
Easy way to check this is just to take the external hose off the outside of the spectrometer and bridge it with a small piece of hose. If it pumps down great that way, check your interior hoses/counter.
I think our 733 gets from atmosphere to the diffusion pump switchover in nine minutes, and we get the ready light by about 15 minutes (6 minutes after switchover to diffusion pump). That's from memory so I might be off a bit.
Steven Cogswell, P.Eng.
The superprobe I am working on is having vacuum trouble. We need to run the
roughing pump for an extended period of time to reach low vacuum and turn on the
diffusion pump, but there is a timer that turns off the system if high vacuum is
not reached in 30 minutes. How can I disable the timer? I have tried adjusting
the potentiometers on the manual pump control panel so that all three pressure
meters report high vacuum, but it still did not disable the timer.