Metrohm 791 VA Detector - Manual (Page 38)

4 Maintenance – Malfunctions
791 VA Detector
32
4.3 Malfunctions and their rectification
Malfunction Cause Rectification
No signal • VA Detector is in "stand-by"
mode.
• VA Detector switched off or
disconnected from mains
voltage.
• Recorder switched off or
disconnected from mains
voltage.
• Recorder disconnected from
VA Detector.
• Electrodes disconnected.
• Broken interconnecting
cables.
• Press "meas" button on VA
Detector.
• Connect VA Detector and
switch on.
• Connect recorder and switch
on.
• Connect recorder to the VA
Detector.
• Connect electrodes.
• Use new interconnecting
cables.
VA Detector
shows "overload" • Current range set exceeded
by too high a concentration of
substance.
• The VA Detector is either
incorrectly balanced or not
balanced at all.
• Reference electrode discon-
nected.
• Auxiliary electrode discon-
nected.
• Polarization voltage badly
adjusted.
• Wait or set a higher current
range at the VA Detector.
• Balance the recording instru-
ment and VA Detector correctly.
• Connect reference electrode.
• Connect auxiliary electrode.
• Adjust polarization voltage
correctly.
Excessively high
background current • Polarization voltage too high.
• Eluent contaminated.
• Eluent contaminated by Fe(II)
ions from rusty steel parts
(traces only suffice!)
• Polarization voltage should
generally not be set higher than
1200 mV.
• Prepare fresh eluent using only
the purest (AR grad) chemicals.
• Check entire HPLC or IC system
for rust; check resistance of all
materials to the reagents in use.
Baseline unstable • Highly retarded or enriched
components from the separat-
ing column.
• Pressure fluctuations due to
poor seals, blocked filters or
capillaries, defective pump,
etc.
• Eluent contaminated by Fe(II)
ions from rusty steel parts
(traces only suffice!).
• Defective reference electrode.
• Rinse the column well with
eluent or regenerate it, use new
column if necessary.
• Check HPLC or IC system for
these faults.
• Check entire HPLC or IC system
for rust; check resistance of all
materials to the reagents in use.
• Replace reference electrode.