Pfaff coverlock 4872 User manual

coverlock
4872
Service
Manual
1st Edition February 1999

1
Page
Table of contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Notes on the sewing machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Specifications of the coverlock 4872 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Adjustment gauge of the coverlock 4872 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Dismantling the housing of the coverlock 4872 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Requirements for adjusting the coverlock 4872 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Needle bar height and needle penetration points
1. Setting the needle bar height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Feeding system
2. Setting the main feed dog in the sewing direction with regard
to the needle plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
3. Setting the feed dog height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
4. Setting the differential feed dog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
5. Setting the main feed-dog height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
6. Setting the presser bar height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
7. Setting the differential feed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
8. Setting the movement of the feed dog stroke and the upper blade . . . . . . . . . . . . . . . . . . . . . .26
9. Setting the feed dog movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Setting the lower overedge looper
10. Setting the height of the lower overedge looper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
11. Setting the timing of the lower overedge looper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
12. Setting the looper-to-needle clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
13. Setting the lateral clearance to the left needle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Setting the upper overedge looper
14. Setting the lateral clearance to the left needle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
15. Setting the timing of the upper overedge looper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
16. Setting the clearance between the upper and lower overedge loopers . . . . . . . . . . . . . . . . . . . .38
Setting the two thread chainstitch looper
17. Setting the lateral clearance to the two thread chainstitch needle “L2” . . . . . . . . . . . . . . . . . . . .39
18. Setting the looper-to-needle clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
19. Setting the ellipsoidal movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
20. Setting the timing of the two thread chainstitch looper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Setting the needle guards
21. Setting the rear needle guard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
22. Setting the needle guard for the cover stitch needles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
Setting the upper blade
23. Setting the upper blade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
24. Setting the lower blade bracket and the seam width adjusting knob . . . . . . . . . . . . . . . . . . . . . .49
25. Setting the chaining finger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

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Setting the looper thread guides
26. Setting the looper thread guide of the lower and upperoveredge loopers . . . . . . . . . . . . . . . . . .51
27. Setting the looper thread guide of the two thread chainstitch looper . . . . . . . . . . . . . . . . . . . . .52
LCD test mode, setting the thread tension and the synchronizer
28. LCD test mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54
29. Setting the synchronizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
30. Setting the background lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
Safety test
31. Microswitch functional test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
32. Electrical safety test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
33. Electrical safety test with ABB Metrawatt M 5013 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
34. Measures to be taken in the case of inadmissible test readings . . . . . . . . . . . . . . . . . . . . . . . . .68

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Foreword
This service and repair manual is designed to help you carry out all repairs on the machine quickly and
correctly.
Adjustments should only be made if the settings deviate from the requirements described here.
When checking or adjusting a machine, always proceed in the order described here.
For easy reference every workstep is marked with a dot.
Differing worksteps are marked with a circle or square.
The indications “right”, “left”, “top”, “bottom”, “front” and “back” always refer to the upright machine with the
controls facing the operator.
When assembling dismantled machines, set the machine to approximately the right settings.
This makes any subsequent fine adjustment much easier.
Unless otherwise specified, the handwheel must always be turned to the front.
When carrying out maintenance work or when replacing mechanical parts or accessories the machine is
to be separated from the power supply by unplugging the mains plug.
An electrical safety test must be carried out following repair work, including mechanical repairs.
According to the German Machine Safety Act of 24.06.1958, VDE regulations are the recognized rules in
the field of electrical engineering and form the basis for electrical safety tests of technical appliances.
The required electrical tests for appliances are contained within the regulations for the repair, modification
and testing of used electrical appliances (VDE 0701, edition 05.93), laid out in section 4.
It is obligatory to test our electrical appliances according to VDE 0701 following any repairs to our electri-
cal appliances.
Outside Germany similar regulations apply which are on the whole identical to the requirements of VDE
0701.
Please also observe sections 32 to 34 of the adjustment and repair instructions.
Therefore a specialist must always be consulted when carrying out repairs on electrical appliances.
The microswitch must always be functionally tested following all repair work.

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Notes on the sewing machine regarding ambient conditions,
handling, cleaning and safety
Ambient conditions:
The recommended ranges are:
Ambient temperature - 10° C to 40° C
Humidity 20 % to 80 %
This machine is a high-quality electro-mechanical device, designed for supervised use at home.
Make sure that it is not subjected to:
dust, high humidity, direct sunlight, static electricity, heat-producing objects, corrosive chemicals or liquids.
The machine must be placed on a flat, stable surface allowing good ventilation.
Handling:
Always make sure not to damage the machine by knocking or dropping it.
Cleaning:
Housing:
To clean the housing, use a dry, clean, soft, lint- free cloth.
To remove any stubborn stains, use a soft cloth with a neutral cleansing agent for plastic materials.
Note:
Do not use any insecticides or chemical products such as petrol or liquid chemicals to clean the housing.
Display:
The display can be cleaned if necessary using a soft cloth moistened with a little water.
Safety:
1. The machine must be commissioned in accordance with the indications on the specification plate.
2. Do not insert any objects into the machine’s openings.
3. Do not use the sewing machine if:
– there is visible damage
– improper function
– it is wet, e.g. condensation.
4. Do not pull the mains plug out of the socket by its cord.
5. Should this appliance be used for a purpose other than that intended, or if it is incorrectly operated,
then we will not accept liability for any damage caused.
6. To avoid the risk of electric shock, do not open the machine. There are no parts inside the machine
which can be repaired by the operator. This is solely the responsibility of our qualified service staff.
7. Only original PFAFF parts are to be used.

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Specifications of the coverlock 4872
Number of needles and threads: 2 needles, 5-, 4- or 3-thread
1 needle, 2- or 3-thread
Needles: system ELx705, cat. no. 2002
thickness Nm 80/12, 90/14
Seam width: 1.4 mm – 9.0 mm
Adjustable cut width: 2.5 mm
Cover stitch width: 2.5 mm, 5.0 mm
Stitch length: 0.5 mm – 4 mm adjustable
Lubrication: manual
Differential feed: 1:0.5 ~ 1:2
Presser foot height: 4.5 mm
Overedge stroke: 2.0 mm
Presser foot: exchangeable
Adjustable presser foot pressure: 6 positions
Edge-blade stroke: 7.2 mm
Glare-free sewing light max.: 12 V, 5 W, bayonet socket
Master switch: for motor and sewing light
Motor: 110 - 127 V
50 - 60 Hz 140 W
220 - 240 V
50 - 60 Hz 145 W
Max. sewing speed: 1500 stitches per minute
Foot control: electronic control
Machine dimensions: width: 355 mm, height: 290 mm, depth: 300 mm
Weight: approx. 10 kg

6
A= Needle bar height (12.0 mm)
B= Presser foot height (4.7 mm)
C= Clearance of upper overedge looper to left needle (6.0 mm)
D= Clearance of lower overedge looper to left needle (2.8 mm)
E= Height of lower overedge looper (65 mm)
F= Clearance of two thread chainstitch looper to needle “L2” (1.6 mm)
G= Height of feed dog (1.3 mm)
H= Clearance between the main and the differential feed dog (3.2 mm)
I= Clearance of the looper thread guide to the upper overedge looper (47.3 mm)
Adjustment gauge of the coverlock 4872
Order number: 29-924 993-82/032

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Dismantling the housing of the coverlock 4872
●Remove the mains plug from the machine.
●Unscrew and remove the fastening screw 1 (fig. 1).
●Remove the presser foot holder completely.
●Remove the needles.
●Remove the spool disc and the thread spool centering pieces (fig. 2).
●Push the complete thread spool stand forward toward the machine.
●Unscrew and remove the fastening screw 2.
●Push the complete spool stand slightly to the right and remove to the rear.
●Unscrew the fastening screw 3 (fig. 3).
●Remove the face cover to the left.

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●The following parts are now removed to the right (fig. 4):
1. Stitch length adjustment knob 4 and the regulator wheel 5 for the differential feed
2. Presser foot 6
●Remove the covers 7 on the stand cover.
●Unscrew and remove the fastening screws 8 on the stand cover.
●Remove the stand cover carefully to the right.
●Unscrew and remove both fastening screws 9.
●Slightly raise the arm cover at the front near the plus/minus keys until the covers are free.
●Remove the arm cover carefully toward the front.

●Turn the handwheel in the normal direction until the needle bar is at its highest position.
●Push the looper cover as far as possible to the right and pull it down.
●Unscrew and remove the three fastening screws 10 on the lower housing panel (fig. 5).
●Remove the lower housing panel.
●Pull the cover 11 slightly on the left and right sides and remove carefully (fig. 6).
●Turn the handwheel in the normal direction until the take-up lever is in the middle of the guide.
●Unscrew and remove both fastening screws 12 on the guide 13.
●Remove the guide 13 with the thread guides 14 and 15.
●Remove the covers 16 (fig. 7).
●Unscrew and remove the fastening screws 17.
●Lift the rear housing panel slightly until the locking pins are clear, then remove the housing panel.
●Pull the front housing panel carefully toward the front (fig. 8, on page 10).
9

10
●Remove the seven cables “A” to “H” from the circuit board.
Note:
The cables “A” to “E” stem from the stepping motors for the thread tension barrels.
The cable “F” is for the PCB/LCD power supply.
The cable “G” is for the stepping motor circuit board.

11
●Unscrew and remove the four fastening screws 18 on the baseplate (fig. 9).
●Remove the machine housing carefully from the baseplate.
●Unscrew and remove the fastening screws 19.
●Remove the swivel plate 20.

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Requirements for adjusting the coverlock 4872
Requirement:
When the needle is at its lowest position, the lower overedge looper must be at the left point of reversal
and the upper looper point, in the downward movement, approx. 5 mm below the needle plate.
The two thread chainstitch looper is at the right point of reversal, when it is at its lowest position.
The eccentrics are set in accordance with the illustrated figures to provide the adjusting requirements.
Check:
1. The screw “a” of the retaining collar 2 must be in line with the screw of the drive eccentric 1 (fig. 6).
The main shaft must not have any axial play.
Turn the handwheel (90°) in the opposite direction of the normal direction. Check whether the screw of
the retaining collar 2 and the eccentric 3 are aligned (fig. 5).
2. Turn the handwheel in the normal direction until the needle bar is at its highest point (fig. 1).
Check the position of the counterweight A in accordance with fig. 2.
Note:
When the eccentric 3 is set correctly, it is possible to see the fastening screw from above (fig. 3).
3. Turn the handwheel (180°) in the normal direction. Check that the counterweight 9 and the eccentrics
7 and 8 are set in accordance with fig. 4.
4. Turn the handwheel (180°) in the normal direction. Check that the screw “a” of the retaining collar and
the screws of the eccentrics 1,6 and 7 are set in accordance with fig. 6.
5. Turn the handwheel (90°) in the normal direction. Check that positions of the eccentrics 1 and 4 are
set in accordance with fig. 7.
6. Turn the handwheel (90°) in the normal direction. Check that positions of the eccentrics 4 and 5 are
set in accordance with fig. 8.

13

14
Setting:
●If not set correctly, the screws of the eccentrics, of the retaining collar and of the counterweight will be
loosened.
●The parts must be set accordingly and the screws must be retightened.
Position and function of the eccentrics
1. Drive eccentric for the needle bar movement
2. Retaining collar for the main shaft
3. Drive eccentric for the feeding movement
4. Drive eccentric for upper overedge looper
5. Take-up-lever eccentric for the two thread chainstitch looper
6. Drive eccentric for the lower overedge and two thread chainstitch looper
7. Drive eccentric for the ellipsoidal movement
8. Drive eccentric for the stroke and blade movement
9. Counterweight

15
Notes:

16
Needle bar height and needle penetration points
1. Setting the needle bar height
Requirement:
The vertical clearance between the overedge needle “R1” and the top edge of the needle plate must be
12 mm when the needle bar 1 is at its upper dead center (fig. 1).
Check:
●Turn the handwheel in the normal direction until the needle bar 1 is at its upper dead center (u.d.c.).
●Insert a new needle Nm 90 into “R1”. The needle must be inserted into the needle holder 2 as far as it
will go.
●Check the needle bar height using the adjustment gauge (measurement A).
Setting:
●Remove the face cover.
●Turn the handwheel in the normal direction until the needle bar 1 is at its upper dead center (u.d.c.).
●Slightly loosen the screw 3 of the needle bar connection (fig. 2).
●Move the needle bar 1 upwards without turning it until the needle touches the adjustment gauge (mea-
surement A).
●Tighten the screw 3.
Test:
●Check the clearance.
The needle holder must be parallel to the machine housing.
●The sides of the needles “L0”, “L1” and “L2” must not touch the sides of the needle plate (fig. 3).

17

18
Feeding system
2. Setting the main feed dog in the sewing direction with regard to the needle plate
Requirement:
When the stitch length is set to “4”, the main feed dog must be centered between the front and the back
of the needle plate in the sewing direction (fig. 4).
The main feed dog must also be centered laterally.
Check:
●Loosen the screw 1 on the presser foot holder (fig. 5).
●Remove the presser foot holder 2.
●Set the maximum stitch length and the standard differential stroke.
●Turn the handwheel in the normal direction until the feed dog is flush with the upper surface of the
needle plate.
●Carry out a visual check.
Setting 1:
●Remove the housing cover as described in the adjustment and repair instructions.
●Set the maximum stitch length and the standard differential stroke.
●Slightly loosen both fastening screws 3 (fig. 6).
●Loosen the fastening screw 5 on the retaining collar.
●Move the feed dog carrier 4 with the retaining collar until the feed dog is centered to the needle plate
in the lateral direction.
●Tighten the fastening screws 3 and 5.
Repeat this procedure until the settings are correct.
Setting 2:
●Slightly loosen the fastening screws 3.
●Move the feed dog carrier 4 until the feed dog is centered to the needle plate in the sewing direction.
●Tighten the fastening screws 3.
Test:
●Check the lateral distance between the main feed dog and the needle plate.
●Check that the machine runs freely with the maximum stitch length set.

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