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QM7500 Technical Manual
QM31930/03093 Rev AD Table of Contents i
Table of Contents
Table of Contents . . . i
Introduction . . . 1
Maintenance . . . 2
Startup . . . 2
Shutdown . . . 2
Troubleshooting . . . 3
Servicing . . . 6
Preparing the QM7500 for Servicing . . . 6
Special Notes for Reassembling the QM7500 Printhead . . . 6
Standard QM7500 Assembly . . . 7
Printhead Assembly . . . 8
Controller Assembly . . . 9
Backflushing a Nozzle . . . 10
Backflushing a Valve . . . 11
Replacing the Nozzle Block . . . 11
Optional 7 mm, 15 mm, and 20 mm Nozzle Blocks . . . 12
Replacing a Valve . . . 12
Replacing the Regulator . . . 13
Replacing the Valve/Photocell Board . . . 15
Replacing the Display . . . 17
Replacing the Battery . . . 18
Replacing the Circuit Board . . . 19
Parts List . . . 20
Introduction . . . 20
QM7500 100/240V with US Power Cord . . . 21
QM7500 100/240V with International Power Cord . . . 21
QM7500 100/240V Arabic . . . 21
QM7500 100/240V Chinese . . . 21
QM7500 Printhead Assembly . . . 23
QM7500 Controller Assembly . . . 25
Consumables – Porous . . . 26
Other Components . . . 26

QM7500 Technical Manual
QM31930/03093 Rev AD Introduction 1
Introduction This QM7500 Technical Manual provides you with complete maintenance,
troubleshooting and servicing information for the MSSC QM7500 Ink Jet Printer. It
also contains a replacement parts list.
CAUTION: This manual is designed for use by qualified technicians only. Any
unauthorized repairs will void your warranty. Unless you are a qualified
technician, do not attempt maintenance that is not discussed in the QM7500
Owners Manual (PN QM32004). You may accidentally damage components
resulting in injury or damage to the equipment.
For more information or assistance contact your local distributor or MSSC
Technical Support any time at [phone]; FAX: [phone].\

QM7500 Technical Manual
2 Maintenance QM31930/03093 Rev AD
Maintenance Startup
At beginning of each shift:
1) With the spray cap on the solvent bottle, spray the nozzles with solvent. In
harsh environments, you may need to spray the nozzles more often than once
per shift.
2) Purge the printhead.
3) Check the ink level in the bottle; install a new bottle if necessary. In harsh
environments, or if print quality declines, replace the ink bottle with solvent
and purge solvent through the unit.
Shutdown
If you are shutting down the unit for less than two weeks, simply turn off the
controller. You do not need to purge the printheads with ink or solvent. Also, do not
remove any ink that may have caked on the nozzle block. This will keep
contaminants from entering the nozzles. When you restart the unit, follow the daily
maintenance procedures on page 2.
If you are shutting down the unit for more than two weeks purge the printheads
with porous solvent. Leave the solvent in the ink lines until you restart the unit.

QM7500 Technical Manual
QM31930/03093 Rev AD Troubleshooting 3
Troubleshooting
Problem Possible Cause Solution
Row of keys fail to work. Chips loose on the circuit board. Make sure the RAM chip (U8) and
the software (U7) are properly
installed, and that the Zilog chip is
not loose.
Printed circuit board is defective. Replace the printed circuit board.
(See page 19.)
The green light is on, but the unit
will not print. Wires loose from the barrel terminals. Reseat any loose wires in the barrel terminals. (See Figure A.)
The unit prints intermittently. Wires disconnected from the
barrel terminals. Reseat any loose wires in the barrel terminals. (See Figure A.)
The print light is constantly
orange. Printhead photocell board defective. Replace the printhead photocell board. (See page 15.)
The machine resets itself. Valve shorted out. Replace the defective valve. (See
page 12.)
The unit will purge but not print. Wires loose from the barrel
terminals. Reseat any loose wires in the barrel terminals. (See Figure A.)
A dot or dots missing. Unit ran out of ink. Replace the ink bottle.
Nozzle clogged. 1.Spray the nozzle block with
solvent.
2.Backflush the nozzle. (See
page 10.)
3.Replace nozzle block. (See
page 11.)
Tube and jewel assembly in the
nozzle block cracked, Replace the nozzle block. (See page 11.)
Worn valve. Increase dot size to temporarily
adjust for worn valve.
Valve became loose from the
valve board. Reseat the valve on the valve board.
Valve is defective. Replace the valve. (See page 12.)
Ink line became loose. Reattach the ink line.
Wires loose from the barrel
terminals. Reseat the wires in the barrel terminals. (See Figure A.)

QM7500 Technical Manual
4 Troubleshooting QM31930/03093 Rev AD
One or more valves fail to work,
resulting in missing dots Cable from the controller to the printhead touchedthevalveboard
causing a short.
Secure the cable from the
controller to the printhead with a
tie wrap.
Valve is defective. Replace the valve. (See page 12.)
Valve/photocell board is defective. Replace the valve/photocell
board. (See page 15.)
The unit comes on and the print
key is orange. Unit locked up. 1.Unplug the power supply from the unit, then plug it back in.
2.Zapthecontrollerbykeyingin Z
A P Shift A.
CAUTION: Zapping the controller
will result in the loss of all print
parameter settings (dot size,
character width, print delay). These
will need to be reset after the ZAP
routine.
Note: Always perform the ZAP
routine after replacing software.
The dots are splattering on the
print sample. Printhead too far away from the product. Position the printhead as close as possible to the product without
rubbing against it and no further
than 3/8" (9.5 mm) away.
Note: Avoid contact between the
printhead and the product as this
may cause print quality to suffer.
No power. Unit is not properly plugged in. Plug unit into an appropriate
power source.
Ink is leaking from the regulator. Regulator is cracked or defective. Replace the regulator. (See
page 13.)
The bottle will not engage when
replacing the bottle. Regulatorisnotproperlyseatedin the saddle of the printhead base. Reseat the regulator in the printhead base.
Regulator is cracked. Replace the regulator. (See
page 13.)
Display screen is blank or garbled. Display is defective. Replace the display. (See
page 17.)
Problem Possible Cause Solution

QM7500 Technical Manual
QM31930/03093 Rev AD Troubleshooting 5
Figure A: Barrel Terminal Wiring Diagram
Prints unrecognizable characters
when displayed correctly. Power supply has recycled and the QM7500 has defaulted to the
Hebrew language.
1.Type in the correct language
code for the language you are
using. (If English is the
language being used type
ENGL.)
2.Zap the controller by keying in
ZAP Shift A.
CAUTION: Zapping the controller
will result in the loss of all print
parameter settings (dot size,
character width, print delay). These
will need to be reset after the ZAP
routine.
Message prints backwards or is
too long. One of the two photocells are dirty. 1.Clean the photocells. 2.Manually set the conveyor
direction, eliminating the need
for two photocells. See your
Owner’sManualforinstructions
on setting the conveyor
direction.
Photocell is defective. Replacethe photocellboard. (See
page 15.)
Keyboard is not responding. Contacts on the PC board are
dirty. Clean the contacts.
Contacts on the back of the
keypad are dirty. Clean the contacts.
Problem Possible Cause Solution
light brown
pink
brown
white
red
yellow
purple
gray
green
orange
blue
black

QM7500 Technical Manual
6 Servicing QM31930/03093 Rev AD
Servicing Preparing the QM7500 for Servicing
Before beginning work on the QM7500, follow these steps. Failure to follow these
steps may result in serious injury or damage to the unit.
To begin servicing the QM7500:
1) Remove the ink bottle.
2) Cover the front of the printhead with an absorbent cloth and purge the
printhead to remove any ink from the system.
3) Remove the QM7500 and power supply to a well-lit, static-free workbench.
Special Notes for Reassembling the QM7500 Printhead
Make sure the regulator is properly seated in the saddle of the printhead base to
allow proper connection of ink bottles. Also ensure that the valve retaining clip
offset is facing the valve board to prevent valves unseating from the valve board.
Finally, make sure that valves are properly oriented and seated in the valve board,
and that all wiring and tubing will not be kinked when the printhead cover is
replaced.

QM7500 Technical Manual
QM31930/03093 Rev AD Servicing 7
Standard QM7500 Assembly
1
2
3
4
5
1. Controller
2. Frame
3. Power Supply
4. Bracket Assembly
5. Printhead

QM7500 Technical Manual
8 Servicing QM31930/03093 Rev AD
Printhead Assembly
1
23
4
5
6
7
8
9
10
12
1. Valve Retaining Clip
2. Tubing (Nozzle)
3. Nozzle Block
4. Valve
5. Photocell Board
6. IDC Connector
7. Valve Board
8. Printhead Button
9. Regulator
10. Tubing (Valve)
11. Cable from Controller
12. Printhead Top
11

QM7500 Technical Manual
QM31930/03093 Rev AD Servicing 9
Controller Assembly
1. Gasket
2. Lens
3. Display
4. Tape
5. Controller Bottom Enclosure
6. Printed Circuit Board
7. Keypad
8. Controller Top Enclosure
1
2
3
4
5
6
7
8

QM7500 Technical Manual
10 Servicing QM31930/03093 Rev AD
Backflushing a Nozzle
1) Prepare the QM7500 for servicing. (See page 6.)
2) Remove the printhead cover by removing the three screws from the bottom of
the printhead. With the unit flat on the workbench, place your thumb on the
regulator and press down lightly as you lift up the top half of the printhead.
Note: Hold the components in place with your finger if necessary. Make
sure the valve/photocell board assembly remains in the printhead base.
Also, avoid unnecessary flexing of the cable between the two boards to
prevent damaging the cable connections.
3) From a print sample, locate the nozzle that needs backflushing.
4) Slide out the photocell board.
5) Disconnect the tubing connected between the valve and the nozzle from the
valve end only; allow it to hang free.
CAUTION: Remaining ink pressure may cause ink to shoot out of the
tubing.
6) Place a cloth at the open end of the tubing.
7) Install the cleaner assembly nozzle (from the service kit) on a bottle of solvent.
8) Press the solvent bottle against the clogged nozzle and spray solvent through it
for several seconds.
9) Reconnect the tubing to the valve.
10) Slide the photocell board back into place, photocells facing out.
11) Replace printhead cover, remount, and purge for several minutes.

QM7500 Technical Manual
QM31930/03093 Rev AD Servicing 11
Backflushing a Valve
1) Prepare the QM7500 for servicing. (See page 6.)
2) Remove the printhead cover by removing the three screws from the bottom of
the printhead. With the unit flat on the workbench, place your thumb on the
regulator and press down lightly as you lift up the top half of the printhead.
Note: Hold the components in place with your finger if necessary. Make
sure the valve/photocell board assembly remains in the printhead base.
Also, avoid unnecessary flexing of the cable between the two boards to
prevent damaging the cable connections.
3) Slide out the photocell board.
4) Locate the valve that needs backflushing. (Valves requiring backflushing can
be identified by a print sample or by drooling or leaking ink.)
5) Disconnect the tubing between the regulator and the valve from the regulator.
CAUTION: Remaining ink pressure may cause ink to shoot out of the
tubing.
6) Remove the tubing between the valve and the nozzle from the valve.
7) Install the cleaner assembly nozzle (from the service kit) on a bottle of solvent.
8) Install tubing (from the service kit) on the cleaner assembly nozzle.
9) Connect the tubing from the cleaner assembly nozzle to the outlet (center) port
of the valve.
10) Place an absorbent cloth around the open end of the other tubing connected to
the valve.
11) Plug in the power supply and purge. (See the Owner's Manual for how to
purge.)
Note: If the QM7500 is not purging, you will not be able to run solvent
through the valve.
12) Spray solvent through the valve for several seconds.
13) Disconnect the solvent bottle from the valve port.
14) Reconnect the tubing from the inlet (off-center) port of the valve to the
regulator; reconnect the tubing from the nozzle to the outlet (center) port of
the valve.
15) Slide the photocell board back into place, photocells facing out.
16) Replace the printhead cover, remount, and purge for several minutes.
Replacing the Nozzle Block
Removing the Nozzle Block
1) Prepare your QM7500 for servicing. (See page 6.)
2) Remove the printhead cover by removing the three screws from the bottom of
the printhead. With the unit flat on the workbench, place your thumb on the
regulator and press down lightly as you lift up the top half of the printhead.

QM7500 Technical Manual
12 Servicing QM31930/03093 Rev AD
Note: Hold the components in place with your finger if necessary. Make
sure the valve/photocell board assembly remains in the printhead base.
Also, avoid unnecessary flexing of the cable between the two boards to
prevent damaging the cable connections.
3) Carefully lift the controller mounting frame off the bottom half of the
printhead.
4) Carefully slide up the photocell board.
5) Slide out the nozzle block.
Installing the New Nozzle Block
1) Pull off the ink tubes one at a time. As you disconnect an ink tube from the old
nozzle block, connect it to the corresponding nozzle of the replacement nozzle
block. (See Figure B.)
2) Slide the newly connected nozzle block into its slot in the printhead.
3) Replace the photocell board and printhead cover. Be careful not to pinch any
of the wires in the printhead.
4) Install an ink bottle, plug the system in, and purge the QM7500 with ink to
remove any air introduced into the system.
Your unit is ready to return to normal operation.
Figure B: Valve Board to Nozzle Block Diagram
Optional 7 mm, 15 mm, and 20 mm Nozzle Blocks
An optional 7 mm, 15 mm and 20 mm nozzle block is available for the QM7500
printhead. If you wish to install a 7 mm, 15 mm or 20 mm nozzle block, see the
Parts List section of this manual for ordering information and follow the procedure
for replacing the nozzle block.
Replacing a Valve
Removing the Valve
1) Prepare your QM7500 for servicing. (See page 6.)
Valve Valve
1
2
3
4
5
6
7
2
1
3
5
7
4
6
Nozzle
Block
Front View

QM7500 Technical Manual
QM31930/03093 Rev AD Servicing 13
2) Remove the printhead cover by removing the three screws from the bottom of
the printhead. With the unit flat on the workbench, place your thumb on the
regulator and press down lightly as you lift up the top half of the printhead.
Note: Hold the components in place with your finger if necessary. Make
sure the valve/photocell board assembly remains in the printhead base.
Also, avoid unnecessary flexing of the cable between the two boards to
prevent damaging the cable connections.
3) Slide out the photocell board.
4) Locate the defective valve. (If a valve has shorted, it will usually be locked
open with ink leaking. A good valve has a resistance reading of approximately
16 ohms.)
5) Remove the valve retaining clip.
6) If necessary move aside functioning valves to get to the defective valve.
7) Disconnect both pieces of tubing from the valve.
CAUTION: Remaining ink pressure may cause ink to shoot out of the
tubing.
8) Disconnect the old valve from the valve board.
Installing the New Valve
1) Connect the tubing from the ink manifold to the intake (off-center) port on the
new valve.
2) Connect the tubing from the nozzle to the outlet (center) port on the new
valve.
3) Plug the new valve into the valve board.
4) Replace the valve retaining clip.
5) Slide the photocell board back into place, photocells facing out.
6) Replace the printhead cover, remount, and purge for several minutes.
Replacing the Regulator
Removing the Regulator
1) Prepare your QM7500 for servicing. (See page 6.)
2) Remove the printhead cover by removing the three screws from the bottom of
the printhead. With the unit flat on the workbench, place your thumb on the
regulator and press down lightly as you lift up the top half of the printhead.
Note: Hold the components in place with your finger if necessary. Make
sure the valve/photocell board assembly remains in the printhead base.
Avoid unnecessary flexing of the cable between the two boards to
prevent damaging the cable connections.
3) Carefully lift the controller mounting frame off the bottom half of the
printhead.
4) Carefully pull the tubing off the regulator ports.

QM7500 Technical Manual
14 Servicing QM31930/03093 Rev AD
Note: Over time the tubing end may stretch. You must trim the tubing to
ensure a snug fit on the new regulator ports.
5) Remove the regulator through the valve board.
Installing the New Regulator
Note: The new regulator has been factory adjusted. Any additional adjustment
will void your warranty and cause operating difficulties.
1) Position the new regulator through the opening in the valve board.
2) Using pliers, carefully slide the tubing onto the regulator ports, one at a time.
3) Replace the printhead cover. Be careful not to pinch any of the wires in the
printhead.
4) Secure the printhead halves with the three screws.
5) Install an ink bottle, plug the system in, and purge the QM7500 with ink to
remove any air introduced into the system.
Your unit is ready to return to normal operation.

QM7500 Technical Manual
QM31930/03093 Rev AD Servicing 15
Replacing the Valve/Photocell Board
Removing the Valve/Photocell Board
1) Prepare your QM7500 for servicing. (See page 6.)
2) Remove the printhead cover by removing the three screws from the bottom of
the printhead. With the unit flat on the workbench, place your thumb on the
regulator and press down lightly as you lift up the top half of the printhead.
Note: Hold the components in place with your finger if necessary. Make
sure the valve/photocell board assembly remains in the printhead base.
Also, avoid unnecessary flexing of the cable between the two boards to
prevent damaging the cable connections.
3) Carefully lift the controller mounting frame off the bottom half of the
printhead.
4) Carefully pull the tubing off the regulator ports.
Note: Over time the tubing end may stretch. You must trim the tubing to
ensure a snug fit on the new regulator ports or you may need to replace
the tubing.
5) Pull the tubing (all of it) through the opening in the valve board.
6) Disconnect the IDC connector from the valve board.
7) Remove the regulator.
8) Slide out the nozzle block; leave the valves connected to the nozzle block.
9) Slide out the valve/photocell board assembly.
10) Remove the valve retaining clip.
11) Disconnect the valves from the old valve board taking care not to bend or
break valve leads.

QM7500 Technical Manual
16 Servicing QM31930/03093 Rev AD
Installing the New Valve/Photocell Board
1) Plug the valves in on the new valve board. (See Figure C.)
2) Carefully slide in the new valve/photocell board assembly.
3) Slide the nozzle block into position.
4) Slide in the valve retaining clip and seat the valves.
5) Reposition the regulator.
6) Plug in the IDC connector.
7) Pull the tubing back through the opening in the valve board.
8) Reconnect the tubing to the regulator.
9) Replace the printhead cover, remount, and purge for several minutes.
Figure C: Valve Board to Nozzle Block Diagram
Valve Valve
1
2
3
4
5
6
7
2
1
3
5
7
4
6
Nozzle
Block
Front View