UBI EasyCoder 501 – Service Manual
199
26. TROUBLE SHOOTING, cont'd.
26.5
Paper Rewind Troubles
• Check that the paper is fitted correctly and that the rewind guide
is fitted described in chapter 8.5.
• Check the tension of the belts to the rewind unit and to the rewind
roller (see chapter 9.3).
• If the rewind unit slips, check if the friction felt inside the rewind
unit has become dried out, see chapter 9.4.
• If the rewind unit does not rotate at all, the stepper motor could be
incorrectly connected (P-400), or its drive circuits, IC-400 and
IC-401 on the CPU board could be damaged.
Check that all pins in the connector of the stepper motor's cable
are fully inserted.
Test that current is supplied through both motor windings by
means of an oscilloscope whose one probe is to be connected to
GND4 and the other probe to P-400:pins 1, 3, 5, and 7, sequentially.
The voltage should switch between 40V and 0V.
Also test the motor current by setting the second probe to each pin
16 of IC-400 and IC-401. The curve traced by the oscilloscope
should indicate a few tenths of a volt at intervals defined by the
stepping rate (magnitude: milliseconds).
If these measurements deviate from what is normal, check the
incoming signals ST 1-3 and ST 4-6 to IC-400 and IC-401,
respectively. They are all TTL level signals, and should vary
between low and high with a frequency in the range of kilohertz.
If they are found OK, the control and drive circuits IC-400 and IC-
401, or the CPU board, are probably damaged and whole board
needs to be replaced.