Agilent 7820A Pressure/Flow Issues

[davebone]

So I have a 7820 that I am trying to work on and it is giving me fits. First off, it is a p/p and s/sl with dual FID. There was not an ALS installed and I installed that. Before installing the ALS board, everything worked like it was supposed to. Detector flows as shown on the GC were the same as measured out the detector and all pressures on the inlets were correct. Now, after the ALS has been installed, the front FID board takes a nose dive and blows something and when you turn on the GC, it will not pass initial self tests. When I remove that board, everything is fine, except I cannot use the front detector. Second, when measuring flows on the back detector, lower flows (such as 40 mL/min) cannot be achieved according to the GC but when measured out the detector, I am reading upwards of 140 mL/min. If I increase the flow to 100 mL/min, the GC thinks it is reading that, but measured flow is 15 mL/min. Last, I cannot maintain pressure on my split/split-less inlet. It reads a constant -0.5psi no matter what I set the pressure to.

I have completely leak checked everything (no leaks.) I initially had the plumbing routed to both inlets and detectors but have only connected to one inlet/detector and still have the same issues. Both inlets have new liners/septum/gold seal (where applicable.) I have also performed a jet test on the back inlet and H2 set to 75mL/min reads 0.22 mL/min on the makeup.
I have also zeroed the channels according to the manual for all involved. I also have updated the frit details for each FID as downloaded from the latest file from Agilent.

If anyone has any suggestions, please let me know. Thank you.

[James_Ball]

Sounds like you could have something shorted on the ALS board. Check to make sure all the pins on the board are straight and not bent or smashed.

I had one once on a 5890 that one pin got folded over when installing and it caused all kinds of problems.

[davebone]

I have disconnected the ALS board from the main board and I am still having the same issues.

[uzman]

It is time to check all fuses , if the fuses are o.k. , swap the FID boards .

[davebone]

Fuses have all been checked and are good. I replaced them anyway. Swapping boards is not that easy as you must "uninstall" the detector from the GC via the software and then reconfigure it. So, after figuring this all out, I was able to switch the one good board from back to front detector and determined that it works and both FIDs lite. I am thinking now I need to purchase a new board.

[davebone]

This still leaves my second issue of pressure readings. My split/splitless inlet still will not get up to pressure but my purge packed inlet will. Also, my FID H2 readings I have to set at 50 mL/min just to get the GC to read the same on the setpoint and actual. But measured flows are actually much higher (130 mL/min.) Air does the same thing but make-up gas does not. I have thoroughly checked for leaks and have found none. If anyone has any suggestions, I would love the assistance!

[uzman]

I don't know , if the EPCs can also be configured , split/splitless and p/p EPCs must have different gas control ranges , may be they are mixed up.

[James_Ball]

If the detector or als board did cause a short, then it might be possible that the calibration tables for flows got reset to default and are no longer reading correctly.

[davebone]

Thank you everyone for your help, the problems have been fixed.

The SS inlet not building pressure was a bad purge trap. Replacing that fixed the issue.

There was a bad FID board that prevented the GC from powering on past self test. I replaced the board and the issue was fixed.

As for the misreading of the FID flows on H2 and Air, that took a little longer. It happens that each time you load the FRIT constants, it doesn't overwrite the previous values but builds on them. To reset this, you hold in the START and PREP RUN buttons while restarting the GC from the OFF position. This cleared all previous values (while leaving configurations and set points) and allowed me to reload the correct FRIT constants and it started working as it should.

Again, thank you everyone. Have a great day!