HEIDENHAIN TNC 407 (243 020) Service Manual - Manual (Page 43)

31-O
SERVICE MANUAL TNC
Issue:
01.09.1995
Kundendienst
Page 36
8.4 Checking the Power Supply (Power Supply Unit)
Two low-voltage fuses are located on the power supply assembly. The fuse F protects the output voltage
of BE and the fuse F protects the remaining voltages (see block diagram, section 8.3.1). If an error
occurs in the power supply (all voltages are missing), first check the at the supply line and then the low-
voltage fuses.
By means of the test load unit, the power supply can be checked fast and easily. For this purpose the
connectors to the power supply boards must be disconnected from the power supply and connected to the test
load unit.
The different values can be measured at the sockets of the test load unit with a multimeter. The values and
their tolerances can be seen from the table in section 8.3. If the measured values deviate distinctly from the
values in the table, the power supply assembly is defective.
If no test load unit is available, the voltages can be measured at the measuring points on the processor board,
the CLP board or the PLC graphics board. (Measuring points: see section 8.5)
The voltage of BE is not required for the TNC as the VDU has its own power supply,
Always switch off the main switch before engaging or disengaging any connectors
The power supply unit does not function during free-run (basic load is required).