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5 INSTRUMENTS, MEASURING IN FLOATING MODE
Battery-operated digital multimeters are suitable for conducting measurements. They can also
test diodes and transistors in many applications. Only high-quality, interference-proof instruments
(e.g. Fluke 75) are suitable for measuring output voltage.
On TIG systems, do not attempt to measure on the load side of the HF reactor (X3) as the voltage
of the HF pulses is so high that it could destroy the instruments. Preferably, measure at the con-
nection for MMA (X7).
When an oscilloscope is used for measuring, it should be powered from an isolating transformer.
Otherwise, connect the measuring earth to the protective conductor.
When the oscilloscope is powered via an isolating transformer and a disconnected protective con-
ductor, the enclosure of the oscilloscope has the potential of the measuring earth selected and
must not be 'touched' by a high voltage (e.g. link voltage).
When two probes are used, make sure that the earth terminals are connected to a common point.
For current measurements, current-measuring prongs are suitable for DC and AC current. An os-
cilloscope should be used to check the correct welding process as well as waveform in case of
AC current. The current can be measured via a suitable shunt or a transformer shunt.
6 OPENING THE SYSTEM
This section describes the enclosure of the DTG405, how to open the unit and how to dismantle
it to a certain degree. Depending on how the fault can be localised, not all of the steps may be
necessary.
Do not start by slackening screws on the base plate since you might accidentally loosen magnetic
components, power rectifier, or heat-sink mounts.
1. Pull the mains plug.
2. Unscrew the U-shaped cover.
3. Unscrew the side panel at the bottom on each side.
4. The side panels of the power block can be removed from the side without having to disman-
tle the entire power block.
5. Discharge the electrolytic capacitors (with resistance).
6. You can remove the connections, i.e. the busbars, between the heat sink modules by slack-
ening the screws.
7. You can unplug or unscrew all the cables leading to the heat sink modules. Before unplug-
ging, make sure you mark their position. This will avoid incorrect wiring later when you re-
assemble the module.
8. The heat sink modules are secured in their holders by screws on the sides. You can remove
each heat sink module separately.
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