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LST700 SERIES INSTALLATION & MAINTENANCE MANUAL • Approved Document No. DFU7002012 Rev 4
LST700 SERIES FIRE ALARM PANEL
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The primary mains fuse (F1) is ruptured.
Symptoms: the panel runs on batteries, but not on mains. The red hazardous voltages present
light on the Power Supply PCB is off.
Suggested action:
(a) Isolate the mains supply, remove the Main Control PCB and check the PSU’s primary
mains fuse (F1) for continuity.
(b) If the fuse is ruptured it will be due to an excessive mains surge or a PSU fault.
Check the components on the PSU for damage. If none is found replace the fuse with the
correct type and reconnect the mains supply. If the red lethal voltages present light does not
come on then the PSU is faulty and should be replaced.
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The battery fuse (F2) is ruptured.
Symptoms: the panel runs on mains, but not on batteries.
Suggested action:
(a) Isolate the mains supply and disconnect the batteries.
(b) Remove the Main Control PCB and check the Battery Fuse (F2) on the Power Supply PCB
for continuity.
(c) If the fuse is ruptured check the Power Supply PCB and Main Control PCB for signs of
damage. If none is found, replace the fuse with the correct type, ensuring that the fuse clip is
not damaged when re-inserting the fuse.
(d) Refit the Main Control PCB and reconnect the batteries.
If the green ‘Supply Present’ light is lit, reconnect the mains supply and check that the power
supply fault has cleared. If the ‘Supply Present’ light is not lit, either the Power Supply
PCB or the Main Control PCB is faulty and should be replaced.
(e) If the Battery Fuse (F2) is intact, proceed to check the battery voltage (see below).
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The battery voltage is too low.
Symptoms : the panel runs on mains, but may or may not run on batteries.
If the mains supply has failed and the battery supply has been discharged to the point where
the voltage is too low (i.e less than 21V), the panel will automatically turn off to avoid damaging
the batteries by allowing them to deep discharge. The panel will not restart unless fresh, fully
charged batteries are connected, or the mains supply is restored.
If the mains supply has not failed, but the total battery voltage is less than 21V, the PSU will not
charge the batteries to avoid damage to the charging circuit. If the batteries can be charged, the
panel will still show a power supply fault until they have sufficient charge, at which point the power
supply fault will automatically be cleared. Depending on battery size and the depth of discharge,
this may take several hours. If the batteries are in poor condition they must be replaced.
Please note that the charging circuit is set up during manufacturing, and is temperature
compensated. There is no need to adjust the voltage.
If the batteries are in good condition and all the other checks have been performed and no
faults found, the Power Supply PCB is faulty and should be replaced.
NB: batteries that are not connected, connected in reverse or with opposite polarities will also
cause a power supply fault condition.
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Supply Present light not lit
If the supply present light is not lit one of the following faults has occurred:
(1) Both the mains supply and the standby batteries have failed. This could be because the
mains supply has failed and the batteries have been exhausted.
Suggested action:
Restore the mains supply and the ‘Supply Present’ light should come back
on. However, if the batteries are discharged this will be recognised as a fault by the panel and
indicated as such. See “Battery voltage too low” above.
(2) The Power Supply PCB, the Main Control PCB and/or the cable that connects them is faulty.
If the mains supply is present (indicated by the red lethal voltages light being lit on the Power
Supply PCB), check that the connector cable between the Power Supply PCB and the Main
Control PCB is fully inserted at both ends. If so, either the Power Supply PCB and/or the Main
Control PCB and/or the connector cable are faulty and should be replaced.
