"caused by a 'fault' signal sent by the degasser to the pump" - - That is correct and means you have your HPLC degasser module correctly connected and installed. The remote cable connection to the degasser was put there as a last ditched effort for the system to tell the customer that their degasser module has been broken for some time and requires professional service. *The RED error status light was already on. Long before the RED light came on, the YELLOW status light on the degasser was lit up all of the time indicating the degasser required service. These features are in place to let you know there is a problem which needs to be addressed.
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coupling the pressure sensor to the pump and solenoid, I see pattern where it pumps down, then within 20 seconds releases pressure through the solenoid, then pumps down again, repeat.
Vacuum obtained on the vacuum output terminals gives a value slightly above 600 mv." - - For the G1322A, with just the pump connected to the sensor, it should pull a very strong vacuum, hit the set point and the pump should turn off for a LONG time. If you hook up the solenoid valve between the sensor and vac pump, then the pump should do the same thing, but this time with the solenoid stopping the pump a bit earlier in the cycle to vent the pump (but still hold vac). The slightly greater than 600 mV signal is typical, but because most of the circuits loose calibration over time it no longer is reliable of any actual vacuum reading so of little value in troubleshooting exc to show you have vacuum.
If your vac pump is bad, then so is your vacuum valve too. The valve acts as a sort of prefilter for the pump (not by design, but by its position inline). As the parts break down, the valve sends contamination to the vac pump. A weak valve damages and accelerates the wear on the vac pump. Replace them both, and also, all of the internal vacuum tubing too. These are normal wear-tear items which often last no more than 5 years.
Please, NEVER EVER install "
Auto-Store" tubing in this or any other HPLC degasser module. Very bad advice. DO not use the G1379-# tubing kit either (that is the wrong kit for this module). Only ultra high purity vacuum rated tubing must be used in this application. If you use cheap tubing from the auto or home center store (usually it is windshield washer fluid tubing), then your degasser will now act as a contamination source for your entire HPLC (or worse yet, an LC-MS system). All of those plasticizes inside that cheap tubing will be mixed with the mobile phase vapors/condensate and re-introduced back into your mobile phase and column. We have serviced many degasser modules over the years where some amateur did just that and contaminated a company's instrument. Use the correct parts for the job.
You did not mention if you checked the condition of the G1322A's 4-CH vacuum chamber (the most expensive part in the whole module,
ping). Replacing the vac pump, valve and/or tubing in a system with a leaking or contaminated 4-Channel vac chamber will lead to early failure of the vac pump and vac valve, wasting money and time. If possible, have the vac chamber professionally tested for leakage rate (which requires professional vac equipment and someone in industry experienced in doing this test that understands what the readings mean and what is pass/fail for a leakage rate) and checked for contamination, esp if the degasser is more than 5 years old. If these services are not available locally and you suspect the chamber is leaking, it may be cheaper to buy a new degasser rather than wast money swapping parts.
For service of the G1322A in Europe, Agilent Techn is probably your best bet. In the USA, for the lowest cost, professional service of any model or brand of HPLC degasser see this info for the repair services we offer;
http://www.chiralizer.com/uploads/8/9/7 ... s_page.pdf