Nulling Problems 331/341

If you are unable to Null or Zero a 331 or 341 instrument (Pre C revision)Power
If you are running on batteries see if the battery indicator in the display is on. 
If the battery indicator is on your lamp is not recieving enough power to function properly.
If your unit is pre 1994 and hasn't been repaired/updated you will need to charge your
batteries to use it.  Plug in the adaptor, turn it off on the bottom and allow it to charge.
For newer units or ones that have been repaired/updated you can plug in your unit
to use it.  To recharge it for battery use you will have to turn it off on the bottom, you can't
run and charge at the same time.

Do NOT Mix 331C and 341C AC Adaptors(SE30-177 or SE30-277) with older 331/341 units(SE30-45).  They are not compatible and can damage an instrument.

Check the light source and the aperture!

Is there an aperture in the instrument? Each instrument comes with a 1mm and 2mm aperture.  The aperture is the black disc in the center of the target window, where the lamp light can be seen.  You must have one installed to use the unit.  Dust buildup below the aperture on the green IR glass will also cause problems.  Remove the aperture to clean, (it will lift out with your fingernail). The green glass should be cleaned periodically using a Q-Tip and glass cleaner.

The Lamp should turn on when pressing the Measurement button.  If it doesn't verify power (see above) try lamp replacement  or send in for service.
 

Ensure that the optics are in good alignment!

The diffuser cell optics is directly above the aperture on the underside of the top half. It is important that it matches up with the aperture when taking a reading. Misalignment of the optics with the aperture will cause inaccurate and/or inconsistent readings. TO CHECK: Turn unit on, close unit with no film and press the read or lamp button. The target window will light. If you look between the top and bottom you can tell if the two discs line up (sit directly over top of each other). Often you will find that the top is offset to the left or right. If so, simply take the heel of your hand and press the top of the unit back towards center. The arm is mounted on an aluminum plate and will re-align if not bent too severely.