10.8 ±15V Power Supply Check
If the display works perfectly but the oscillator output is at a very low level, or if the
measuring set is measuring an incorrect level then the ±15V should be suspected.
Using the 0v reference point on the top board as a 0V reference, check that the ±15V at
the two labelled test points/links (to the left of the DC-DC convertor on the top board) is
within ±5%. Low voltage may be the result of a faulty DC-DC convertor or excessive
load from the bottom board. If in doubt, check the current by opening one of the 15V
links and inserting an ammeter in its place. Normal current should be around 35mA
(LA101) and 38mA (LA102), 40mA maximum. Try a good DC-DC converter from a
different unit and repeat the tests.
If the 15V current consumption is high turn the unit off, disconnect the ribbon cable to the
bottom board (PL2) and repeat the tests. If it is still very high the fault is on the top
board, otherwise it is probably on the bottom board. In either case it is often possible to
locate the fault by feeling the ICs on the suspect board to see if any feel hot (the DC-DC
converter, IC18 5V regulator and the AC-DC convertor all run hot, but all other
components should be quite cool).
10.9 Battery Testing
This section refers to lithium-ion batteries as used in the LA100 MK3, if you have an
earlier unit with NiCAD batteries please refer to section 10.9 of the fifth edition manaul,
which is available from the downloads section of our website www.lindos.co.uk.
If the unit only works when the battery is disconnected try charging the battery (ie plug
the battery in and connect a mains power supply to the unit). After 20 minutes, turn the
unit off, by temporarily disconnecting the battery if necessary, and turn it back on again.
If the unit still doesn’t work the battery has almost certainly failed. In either case it is
worth testing the battery as described below, but remember that a full charge takes 16
hours. Replacement battery packs are available from Lindos, and unwanted faulty packs
should be returned to Lindos for safe disposal.
Note that non-volatile memory contents may be lost if the battery and the mains supply
are both disconnected for more than a second.
With the mains connected and the battery unplugged measure the voltage V
oc
across pins
1 and 3 of the PL4 connector (fig. 10.2). If it is not within the range 8.35-8.4V then the
switchmode power supply (AC to DC convertor) may be faulty.
Push the battery connector back on half-way to allow for the probes (fig. 10.3) and
measure the battery voltage on charge, V
ch
which should be 6.4-8.4V. If it is lower than
this after 1 minute the battery has probably failed.
162
10. Service Information
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