Warning--Signal level out-of-range in peak

[Les]

I seem to have a problem with hydrogen peak. Using 6890 with an AIB TCD detector. This is a new GC and detector. I can't seem to keep my peak detected. The range has been increased to Range 5. This is a Refinery Gas Analyzer with packed columns.
Using TC6.1 with 900 Interface.
I see the peak on the chromatogram, no flattened areas at the crest. The peak is within 400 mV response but I'm getting a signal range error and I don't understand why? Anybody got some suggestions? What to look for? Anything short of a blunt hammer.

[DR]

Doublecheck the TC method - is the 900 looking for signal in the correct voltage range (0.1, 1, 2V max)?

[Les]

I have played moved the AD range from 2 to 10 V, but that made no difference. The range setting was at 4. Both times the signal out of range. Set the range to 5. (Using 100% hydrogen) First shot was OK second shot out of range.
Then I made adjustment to the zero setting and made a few shots with success, but I still don't understand the reason this is occuring.
As I said, the new TCD is separate from the GC. The GC purchased from AC Controls with a TCD controller box separate from the GC.
I guess I need more infor about this detector.