Schrittmotorenkarte SMC 800 defekt

Some information about the SMC800: (PDF)
http://www.robio.be/cnc/second/Jumbo_plotter/SMC800/SMC800_schematic.pdf

er „zittert“ nur noch....

Inside a bi-polar stepper motor there are two coils.
The SMC800 has an IC for each coil. It is likely that
one of the ICs of the Y axis is defective so this is
way the stepper motor is only vibrating. Try to disconnect
the wire AY. If the Y motor is still vibrating then
IC8 is defective. If the motor is not vibrating anymore
(completely silent) then IC7 is defective. Before you
try that, make sure that the two coils of the motor are OK.
(If one coil of the motor is defective you will see the
same problem).

Reconnect the wire AY and disconnect the wire CY.
What do you see now?

If you have disconnected AY and the motor is still turning,
then IC8 is defective. IC7 and IC8 are driven by IC3 which
is a 74HC574 IC. (See page 2 of the PDF of my previous link).


Replace IC8 and IC7. Not sure which type of IC you will find
(PBL3717A or TEA3717) so if you replace both ICs you will
be sure that the two coils of the motor Y are driven by the
same type of IC. If you still have problems after replacing
IC7 and IC8, then replace also IC3. The heatsinks are glued
on IC7 and IC8 with a 2-component thermal glue. Heatsinks
are mandatory!

Good luck!