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- Posts: 418
- Joined: Mon Aug 15, 2005 3:06 pm
Good Afternoon Chromatographers,
It's been a while because I'm now doing product development and process troubleshooting rather than LC all the time, but I'm back and have an interesting situation with a Waters 2996 PDA:
Until recently, this old beast was stone reliable and has been maintained either by Waters or me for its entire life. As far as I can determine, it's a converted 996 based upon the circa 1992 power supply that's living in an instrument with a circa 2003 serial number.
Anyway, I am seeing short duration negative peaks in the baseline that I believe to be detector related because they occur regardless of whether there is any flow through the instrument at all. All instrument diagnostics pass - I tried to 'run-to-failure' overnight to no avail. Lamp energy is fine - 28-30K, depending on the lamp installed and it does it after I swap lamps. Communication cables between the instrument and the data system are fine - swapping in a second PDA on the same cables gives no problems.
One interesting thing it does occasionally is it appears to shut off the lamp upon making an injection. This is fairly rare, but more common when the instrument is acting up as previously described. What it does is this: Prior to making the injection, both the status and lamp indicators are lit as normal, but upon making the injection the lamp indicator will flash and it's quite clear that the instrument is blind. Stopping the injection and going back to monitor baseline will reset things and the detector will see again. Turning the instrument off and allowing it to cool for a few hours seems to alleviate things as well.
It smells like an electrical issue to me.
What I'm thinking is this: The 24 year old power supply might not be supplying steady enough voltage to the lamp and on a dip that's strong enough, it's actually shutting things down momentarily.
My question: Does anyone know how to check the output voltage on one of these power supplies? Which of the four pins on the lamp plug are the ones to measure? I'm assuming black is ground, blue to supply firing voltage, and red to run (that's where the lamp timer used to be), but I'm guessing.
If there's any wisdom here for this, I'd appreciate it. If not, I'll just swap in another power supply and see what I get. I suppose I could back date the thing to a 996 as I have one of those with a bad optical bench.
It's been a while because I'm now doing product development and process troubleshooting rather than LC all the time, but I'm back and have an interesting situation with a Waters 2996 PDA:
Until recently, this old beast was stone reliable and has been maintained either by Waters or me for its entire life. As far as I can determine, it's a converted 996 based upon the circa 1992 power supply that's living in an instrument with a circa 2003 serial number.
Anyway, I am seeing short duration negative peaks in the baseline that I believe to be detector related because they occur regardless of whether there is any flow through the instrument at all. All instrument diagnostics pass - I tried to 'run-to-failure' overnight to no avail. Lamp energy is fine - 28-30K, depending on the lamp installed and it does it after I swap lamps. Communication cables between the instrument and the data system are fine - swapping in a second PDA on the same cables gives no problems.
One interesting thing it does occasionally is it appears to shut off the lamp upon making an injection. This is fairly rare, but more common when the instrument is acting up as previously described. What it does is this: Prior to making the injection, both the status and lamp indicators are lit as normal, but upon making the injection the lamp indicator will flash and it's quite clear that the instrument is blind. Stopping the injection and going back to monitor baseline will reset things and the detector will see again. Turning the instrument off and allowing it to cool for a few hours seems to alleviate things as well.
It smells like an electrical issue to me.
What I'm thinking is this: The 24 year old power supply might not be supplying steady enough voltage to the lamp and on a dip that's strong enough, it's actually shutting things down momentarily.
My question: Does anyone know how to check the output voltage on one of these power supplies? Which of the four pins on the lamp plug are the ones to measure? I'm assuming black is ground, blue to supply firing voltage, and red to run (that's where the lamp timer used to be), but I'm guessing.
If there's any wisdom here for this, I'd appreciate it. If not, I'll just swap in another power supply and see what I get. I suppose I could back date the thing to a 996 as I have one of those with a bad optical bench.
http://the-ghetto-chromatographer.blogspot.com/
