Section 6 Troubleshooting - Hach MP-4 User Manual

Section 6
Symptom
No display even though
measurement key is
pushed
Inaccurate pH reading
No response to pH
changes (MP-6 and MP-6p
models)
Meter does not adjust
down to pH 7 (MP-6 and
MP-6p models)
pH readings drift or
respond slowly to change
or
FAC displays repeatedly
Unstable conductivity, TDS
or resistivity readings
Meter cannot calibrate
Conductivity or TDS
Resistivity reading is much
lower than expected
Troubleshooting
Possible cause
Battery is weak or not
connected.
pH calibration is needed
(see section 4.9 on page
Cross-contamination from
residual buffers or samples
in sensor cup
Calibration with expired pH
buffers
Sensor bulb is cracked or an
electromechanical short is
caused by an internal crack.
pH sensor has lost KCl
Temporary condition due to
memory of solution in pH
sensor cup for long periods
Bulb dirty or dried out
Reference junction clogged
or coated
Dirty electrodes
Test samples that are
greater than 1 MΩ
Film or deposits on
electrodes
Contamination from previous
samples or from the pH
sensor cup
Carbon dioxide in the test
sample
Action
Check the connections or
replace the battery (see
section 5.2 on page
Recalibrate the meter.
33)
Rinse the sensor cup.
Recalibrate using fresh
buffers.
Replace the pH/ORP sensor
(see section 5.3 on page
Clean and restore the sensor
(see section 5.4 on page
and recalibrate. If there is no
improvement, replace the
pH/ORP sensor (see
section 5.3 on page
Clean and restore the sensor
(see section 5.4 on page
and recalibrate. If there is no
improvement, replace the
pH/ORP sensor (refer to
section 5.3 on page
Clean the cell cup and the
electrodes (see
page 38).
Minimize the test sample
exposure to air (see
section 3.6 on page
Clean the cell cup and the
electrodes (see
).
page 38
Rinse the sensor cup more
thoroughly before
measurement.
Make sure the pH cap is
snugly in place
(see section 5.4 on page
37).
38).
38)
38).
38)
38).
section 5.4 on
17).
section 5.4 on
38).
41