Mp370 2 year old machine, when switched on makes noise of plastic gears jumping, carriage moves slowly to the rhs then swiftly to extreme lhs then message appears in diplay (carriage jammed press ok) if pressed repeats over again

Needs
Cost = £25 for drive belt + any tools needed (saving of £150 - £200).
Tools = Long shafted crosshead screwdriver, 3 & 4 & 6mm hex keys, metric spanners, ratchet tie-down luggage straps (2), wire twists.
Time = 3-4 hours.
Difficulty = Moderate.
General
The 15mm grooved belt is tensioned by a spring loaded jockey pulley. Dealing with this is the crux. Handing is relative to front view of the machine. Beware of magnetic field near brake when running under load - pace-makers, watches etc.
Procedure
1. Disconnect dc supply and remove plug. Clear access is needed to both sides, with most of the work done from RHS.
2. Disconnect both drive arms from the drive discs using hex key. Pull front ends outwards to clear the trunnions. Push both arms back out of the way. (Drive discs cannot be removed without special tools).
3. Remove RHS cover using crosshead driver to undo screws in deep slots round edge.
4. Remove dc socket from LHS cover (hex nut) before removing LHS cover.
5. Working from RHS, note layout of electromagnet brake unit. Cut out old belt. Remove jockey spring.
6. Plates on either side clamp the magnet core. Remove the RHS plate only (which also carries the jockey pulley crank). Remove hex nut on end of brake pulley shaft. Use spanner and hex key to remove 4 long bolts one at a time and partially reinsert each from LHS - this prevents the short aluminium spacers on LHS from falling out. Don't lose the long spacers or the crank mounting bell washer from RHS. Remove 2 short screws from lower edge of plate using hex key. Each has a plain and a spring washer. Do not slacken the corresponding 2 screws on LHS, since that risks disturbing the distance between the driving and brake axes.
7. Remove old belt debris and clean.
8. Pass new belt over RHS drive disc. Fit centrally into grooves on topside of disc only, leaving enough slack to fit centrally round the small brake pulley.
9. Grease mounting washer and replace crank with jockey pulley hanging underneath belt. Refit RHS plate, starting with the spindle hex nut. Take care that each bolt passes through both long and short aluminium spacers. (There seems no reason to remove and reinsert the bolts from RHS - this only increases the chance of dislodging the small spacers). If a spacer does move, use a wire twist to hold in place temporarily while inserting bolt. Ensure that all bolts and screws are fully tightened before step 10.
10. Refit jockey spring, ensuring that the pulley pushes against belt's lower surface. Anchor ratchet tie-down to back foot of machine, wrap round crank arm, then pull back spring as far as possible. Use 2 tie-downs for safety and maximum tension.
11. Slowly rotate RHS drive disc anticlockwise while keeping belt central on both pulleys. Use a screwdriver blade to prevent the belt jumping the grooves on the brake pulley and slipping off the jockey pulley. Once the belt is grooved, keep turning to check that it runs true - no grooves should be visible on the brake pulley. Use side pressure while turning to re-position. Mind your fingers.
12. Release tie-downs very carefully, since the spring reacts with a bang. Temporarily attach drive arms and dc supply. Test. When satisfied that all is OK and belt runs true under load, detach drive arms, replace LHS cover, dc socket, RHS cover, drive arms, and plug in dc supply.