Hi,

I am using 7890GC having TCD and FID detector with a gas sampling valve.
I have an issue with TCD, which shows no peak but the baseline.

Here are the symptoms.
- FID is working well, but TCD is not working.
- I can hear the clicking sound from TCD.
- The baseline of the TCD signal varies when heating the oven, while the baseline was at ~ -1.2 uV to - 0.8 uV.
-> Based on this, I believe the filament is working
- I confirmed the gas flow at the exhaust of TCD, but not measured quantitatively. Just confirmed the exhaust flow by bubbling in water.
- When I switched the column outlet (initially connected to TCD) to FID, FID showed reproducible peaks.
-> Based on this, I believe the connection before the TCD detector works well.
- When I keep the column (GScarbonplot-capillary column 30m 320 um 3 um) pressure at 20 psi, the makeup flow in the TCD detector is always higher than 4 ml/min (even if set point is 2 ml/min).
- When I shut off the instrument, the column pressure, makeup flow, and reference flow decrease very slowly.

Can anyone help me to resolve this issue?