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Intermec EasyCoder 501 – Service Manual Ed. 7
Chapter 26 Troubleshooting
26.1 Printer “Dead”,
cont.
Power Supply failure, cont.
•
A further possible cause of malfunction is that one of the wash-
ers between the transistors and the heatsink is either broken
or incorrectly positioned, which may produce a short-circuit
between the metal housing of the transistor (collector) and the
heatsink (earth).
• The last voltage to be checked is P24. Check voltage at test
point P24 (see Chapter 17.7) during print or cut operation. If
P24 is low, the cutoff transistor Q-704 is broken.
Transformer and cabling failure
•
If the in33V AC from the transformer to the CPU
board (see previous page) is OK and none of the aforemen-
tioned possible causes of malfunction seems likely, one of the
rectifi er diodes D-300, D-301, D-304, or D-306 is probably
damaged.
• If the cause of malfunction is still not found, it is bound to lie
in the cables or components between the AC power cord recep-
tacle and the CPU board.
Check that cables are correctly connected and not defective,
and check all cable shoes for bad contact.
• A further cause of power failure may reside in the transformer
or in the AC power cord receptacle.
With power still switched off, check that the resistance in the
transformer windings is low thus indicating that there is no
interruption.
If the transformer is hot, +100°C or more, the internal thermal
bimetallic cutout may have been triggered. The resistance
between the red and the orange wire will then rise to some
Kohms. Let the transformer cool off and check again.
• If the transformer repeatedly heats up, it has probably got an
internal short-circuit. If so, replace it, as otherwise there will
be a safety hazard, when mains are no longer isolated from the
secondary side of the transformer.