Han's YueMing - Professional Laser Machine Manufacturer

Laser Engraver Repair

Analysis on Common Failures of Engraving Machines
Updated:2010-07-23 16:35  Origin:laser cutting machine  Author:Han's Yueming Laser  Hist:


A、  Shallow and slow engraving

The direct reason for deficient laser engraving depth and speed is:  low effective optical power density

The laser processing effects on different materials mainly depend on the optical power density (not power) imposed on the materials. Optical power density means the power imposed on unit area and its formula of computation is as following:

Optical power density = optical power / beam spot area

Two kinds of resolution derive from this formula: enhance the optical power density or decrease the focusing beam spot area.

Enhance the optical power when finalize the focus:

1.check and clean the light outlet portal  of the laser diode

Check and clean the lens and lens with breakage should be immediately replaced. Molybdenum Reflection Mirror Company provides service of “returning the old for a discount for new” to dramatically decrease the cost of the users. Compulsory replacement of lens for every half a year is advised.

2.Check whether the light route is normal and whether there are the following issues in the process of laser beam transit:

Part of the laser had been kept out. Whether the laser passed the hole of the object from the centre point, if not, it is easy to cause diffraction effect to decrease the laser power and quality. Increase the working current within the limitation of the maximum working current of the laser diode otherwise the laser power will drop. The maximum working current for different laser diodes: 1.2m laser diode: 20mA; 1.6mA: 22mA.

The laser diode may be aging and needs to be replaced.

3.Replace the laser diode with a higher power one.

Decrease the size of the focus point:

For most application circumstances, it’s more effective and cheaper to decrease the beam spot size than to increase the working current of the laser diode or to use higher power laser diode.

Check the quality of the beam spot cast on the focusing mirror:

The higher the quality of the beam spot cast on the reflection mirror, the smaller the size of the focus and the higher the optical power density are. If the quality of the beam spot cast on the reflection mirror is poor, the following measures shall be taken:

Check from the light outlet portal of the laser diode to determine the position that caused the poor quality beam spot. If it’s the reflection mirror that caused the problem, adjust or replace it. If the quality is poor at the very light outlet portal of the laser diode, the following measures should be taken:

Check whether the support is at the correct position of the total length of the laser diode and adjust it if necessary. The correct distance between the two supports is half of the length of laser diode and both ends a quarter overstep.

The supporting direction of the laser diode may be wrong to cause the distortion of the laser diode. Rotate the laser diode to find the best supporting angle (direction).

Note: after rotate the laser diode, the inlet/outlet installation and adjustment of the cooling water should be repeated and the principle of “in lower and out higher” should be observed.

Whether the laser beam is always vertical to the reflection mirror when cast on it:

When the laser beam cast on the reflection mirror vertically at the centre point, the best quality focus point is formed. If the laser beam cast on the reflection mirror tipsily, the quality of the focus will decrease, the beam spot size will increase dramatically and the optical power density will drop a lot to weaken the quality of cutting and engraving process.

Check and adjust the light route of the lens carefully to make the laser casting positions in the four corners firm and reliable. Only if this requirement is met, can the stable optical power density in the whole working process be assured.

Employ the light route verticality calibrator to check and adjust the 3# reflection mirror and to make the laser beam to cast, through the focusing mirror drawtube, on the reflection mirror vertically at the centre point.

Choose the reflection mirror of proper focal distance: (the common focal distance of the reflection mirrors the Company provided include: F=50\ 63.5\75mm)

For the same laser beam, the relationship between the focal distance of the reflection mirror and the focal point size is as follows: the shorter the focal distance, the smaller the focal point size is, and the shorter the depth of field is; the longer the focal distance, the bigger the focal point size and the longer the depth of field are. It’s a contradiction between the size of the focal point and the depth of field. The depth of field is the length of the optical power concentrated area where processing capability is formed by the reflected laser beam. The longer the depth of field, the better it is for processing thick materials; but the cutting capability decrease when the focal point becomes bigger. The shorter the depth of field is, the smaller the focal point and the stronger the cutting capability. The smaller the focal point is, the shorter the cutting depth. At the same time, the requirement for the smoothness of the work station is increased, i.e., it becomes more sensitive to surface unevenness. Thus the principle for choice of lens is: choose the reflection mirror with shorter focal distance as possible. The Company provides reflection mirrors of various focal distances: 38mm, 50mm, 63.5mm, 75mm, 100mm, etc. when the cutting speed cannot meet the requirements of the customers, lens with shorter focal distance should be employed. At the same time, a set of lens with different focal distances is advised for processing requirements of materials with different thickness.

Focusing correctly and keep proper defocusing amount according to the actual situation:

The focusing in actual application should be carefully checked and the correct focusing method is:

Refer to the focal distance of the reflection mirror and experiment several different positions approximate to the focal distance to determine the position with the strongest processing ability and take it as the correct focal distance for application. Even the same lens’ focusing position will be different for different materials and same material of different thickness. That is to say the defocusing amounts are different to different materials and same materials of different thickness. The defocusing amount: the focusing of laser is a process of gathering followed by scattering. Because the superposition between the physical focal point of the reflection mirror and the surface of the material cannot assure the best processing effect, the focal point should be adjusted to a certain depth of the material according to the actual situation to get the strongest cutting ability and the best processing effect. This certain depth is defocusing amount, which is related to the material and its thickness.

Only if it failed to reach the aim after all the above steps, the laser diode and other parts can be replaced.

Check whether the voltage of the wiring panel is correct and the ampere meter should be connected during the whole process to check whether the current is correct.

C、 No laser or weak optical intensity

The control flow of laser operation output is:

        -------Power supply to the system-----

         Main control system laser power supply, laser diode, reflection mirror, process materials for description convenience and according to the control flow, the failures can be classified into front failures and back failures:

Front failures: it means the failures occur at the position in front of the check position. Back failures: opposite to front failures. For example: in this case, it started from check the discharging situation of the laser diode, then the “front failures” mean failures in one or more position of laser diode, laser power supply, control system, system power supply, relative electrical wiring, etc.. The following check procedure was set according to the above mentioned control flow:

b.      Observe the discharging status of the laser diode (glass tube)

Observe the discharging status of the laser diode in working or through spot spray: the colour, the stability, the intension, and so on of the discharged light arc. If abnormal discharging is found, it can be basically judged that it’s the laser diode failure or front failure caused the problem.

If evident abnormity of the light arc colour is found, it can be basically judged leaking or aging laser diode, which needs to be replaced.

Check whether the laser power supply is working correctly.

Check whether the wire connection related to laser power supply is reliable and whether there is any abnormity along the cable.

Press the spot spray button on the laser power supply,

If there is still no discharging of electricity or laser, the most possibility is the “laser power supply” is malfunctioning. Try to replace the laser power supply first and then repeat the above checking flow.

If the repetition of the above steps failed to correct it, the reliability of the electrical wire connection should be checked more carefully and try to replace relative wires with new ones.

If the discharging status is correct, execute the following checking flow.

Check the laser optical intensity at the light outlet portal of the laser diode:

Check and clean the light outlet portal of the laser diode first

Check whether the laser beam is normal through the spot spray button, if not:

It may be necessary to connect the mA meter with the high voltage loop of the laser diode to observe the working current of the laser diode.

Increase/decrease the control current of “laser power supply”. If there is no/small change of the laser extracting from the laser diode along with the increase/decrease of the working current of the laser diode, the biggest possibility is that the laser diode is malfunctioning.

If the mA meter indicates that the working current of the laser diode is not stable, the biggest possibility is that the laser power supply is malfunctioning.

If there is no/abnormal change of the working current of the laser diode, the “laser power supply” or the main control panel may be malfunctioning. Replace one first and then another according to the failure to determine the problematic part.

If all the above steps failed to find out the cause, the power supply of the city and the output voltage and its stability of the switch power on the main board should be tested with a multimeter.

The key point is to check the electric wire connection and cable failure and try to reinforce the wire connection.

Try to replace relative wires with new ones.

Try to replace the power supply (switch power supply) of the main board.

d.Check and clean the following lens and light route

The light extraction from the laser diode is normal, then the failure of no laser or weak laser can only occur in the transit process in the back part and it can be resolved through checking, cleaning, replacement of lens and readjust the light route. 

If the problem remains, i.e., the light route cannot be adjusted to the right position, calibration / adjustment / replacement of mechanical structure or parts may be necessary.

E、 Unstable low optical density

All the laser diodes have the following common feature: the higher the power of the laser diode, the poorer reliability and stability of the low power output. However, in this manual, treatments to failures mean how to enhance the stability of the low power processing under the present conditions.

Failure: uneven depth of engraving and cleaning, which is particularly evident when processing different layer with different power.

Causes to the failure: 1. since the laser diode produces laser emitting through high voltage breakdown, its characteristics are divided into three ranges: low power range means the optical density is under 30% and the output current is under 6mA. Within this range, the relationship between assign and optical density is non-linear and the optical density has a mutation between the 5mA and 6mA. This range increases along with the increase of the rated power of the laser diode. Linear range means the optical density is between 30% and 90%, within which, the laser diode will completely breakdown and the relationship between the assign and the output optical density is linear. The optical power is relatively stable. High power range means the range within which the power is above 90% and the optical power decrease with the increase of the assign. Analysis from the characteristics of the laser diode, the main cause to the unstable low optical density is the non-linearity of the laser diode, especially when mutation occurs in the process of transit from high power to low power, during which the mutant of the laser diode temperature and the high voltage enhance the non-linearity. Method to eliminate this: different methods should be developed and provided for different customers’ processing requirements. 1. Those customers who only process with low power:

The method of increasing the power attenuation can be employed, i.e., to decrease the laser power with used reflection mirror and focusing mirror or double focusing mirror so that the laser diode can be limited to work in the linear range to enhance the stability of laser output.

Employ low power laser diode to reduce non-linear range.

Those customers who process with both high and low power:

This issue can be reduced through changing the processing technology. When layers processed separately, try to allot deep processing and shallow processing equally and try to avoid transit from long-time high power processing to long-time low power processing. Try to allot short-time high power and short-time low power equally to reduce power instability caused by temperature reduction.

Try to minimize the power difference between different layers and 90% high power processing should be avoid. Try to avoid the current between 5mA and 6mA when processing with low power.

Uneven bottom cleaning

Failure: obvious protuberance when cleaning the bottom and unevenness at the cross of longitude and latitude position in intaglio. In rilievi, there are protuberant lines and the deeper the engraving cleaning, the more obvious they are. Causes to this failure:

The processing speed is too fast and the response speed of the laser diode cannot go with it.

  The frequency of the laser control switch is too low and the laser beam is too long with tailing phenomena and is not punctiform.

Air blow amount is not correct to cause protuberant lines formed by connection of powder

Deflective light route or wrong focal distance causes scattering beams and unevenness on the bottom.

It is caused by unreasonable choice of focusing mirror. Try to choose focusing mirror with short focal distance to improve the quality of the laser beam.


Check to assure the light route is right first.

Decrease the processing speed to increase the frequency of laser output switch.

Adjust the air blow amount to avoid powder connection and try to use side-blow.

Choose lens with short focal distance and adjust the focal distance by taking into consideration the depth to be processed.

G、  High Voltage Sparks

Failure: there are two kinds of high voltage sparks: in laser diode sparks and out diode sparks, both with the sound of firecracker. Obvious arc discharges can be found in the laser diode if it’s in laser diode spark and at the spark position if it’s out diode spark. Out diode sparks usually occur at the high voltage connection place or near the high voltage wire. Analysis to the failure:

In diode sparks:

a. not enough water in diode and bubbles in it    b. defective connection of the electrode leader in the laser diode

c. wrong procedure when turn on and power the machine   d. poor quality laser diode

Out diode sparks

a. loose and defective high voltage connector     b. damp air circumstance and too much moisture on the HV connector caused discharge and sparks   c. electricity leakage from the HV wire with abrasion


In diode sparks

Observe whether there are bubbles in the laser diode. If yes, discharge them by standing up the laser diode with the water-in end on top in the precondition that the laser diode is passed through water.

If the sparks occur at the pole, the power supply should be disconnected to check whether the electrode leader is loose and assure good connection of leader.

The steps to electrify the machine are: turn on the main power first and wait until the reset process finished. Then turn on the laser power supply to avoid laser diode sparks caused by preionization discharge of power supply.

Replace the laser diode.

Out diode sparks:

Pull the leaders at both ends of the HV connector to check whether it’s loose and good connection should be assured.

Air around the HV connector should be kept dry and no moisture on the connector base, especially when it’s humid.

HV wire with abrasion must be replaced and binding up with electrical insulation tape is not an option.

Note: HV sparks may cause malfunction of the main board, even system halted.

Scattering beam spot, out focus, hot drawtube, and sparkles at the light outlet portal of the slipper

Failure: when processing, yellow and thick laser beam can be found, the beam spot is hollow and the focusing mirror drawtube is hot if touched.

The temperature of the water in the laser diode is too high.

The lens has been seriously polluted.

The position of the support for the laser diode is unreasonable to cause inner distortion of the laser diode.

Deflective light route and poor focus effect is the main caused of the sparkles at the light outlet portal of the slipper.

The choice of lens is not proper and the processing depth had not been taken into consideration when adjusting the focal distance. These issues caused the poor focus effect.

The laser diode is problematic.


The temperature of the water in the laser diode should be controlled below 32 °C.

Adjust the light route and assure it is correct. Processing depth must be taken into consideration when adjusting the focal distance.

Periodical cleaning of lens required to assure they are clean. Choose proper reflection mirrors to assure good laser beams.

Observe whether the support position for the laser diode is proper and adjust it to the right position if not.

Replace the laser diode.

Uninterrupted / off-and-on laser beams, unstable / uncontrollable current

Failure: all are abnormal light extraction. Serial the ampere meter at the HV end and abnormity, i.e., long-time current, or intermittent current, or even uncontrollable current, will be indicated.

Causes to this failure: the reason for this is mainly the wrong choice of laser diode type, defective connection of main board, wiring panel, power supply, control wire connection, or failure of circulatory water cooling system.


Check whether the laser diode type is correct in parameter setup. It’s the main reason that causes uninterrupted laser beam.

Pull the nine-core control wire to check whether it’s loose. Maybe the connection is not reliable.

Unload the control wire (nine-core wire) and press the spot spray button on the power supply to determine whether it’s problem with the power supply or the main board.

Normal spot spray indicates normal power supply.

Abnormal spot spray indicates that the power supply is problematic.

When the power is normal, connect the control wire and test the control lead pin of the switch on wiring panel with multimeter. If it doesn’t give out light and the normal voltage is above 4V. The main board output will be abnormal if the voltage is below 3V. When giving out lights, the voltage of the pin should be below 2V and the output will be abnormal if it is higher than 2.5V.

Check whether the water circulation is correct, or if there is any interrupted water flow or any problem with the water protector.

I.Auto reset, ceasing engraving, slipping and disordered engraving when processing


Sudden auto reset to cause the machine back to mechanical origin or ceasing engraving, slipping and disordered engraving when processing.

Causes of this failure:

The causes of this failure are mainly loose wire connection of control panel or network, unreliable main board or ground leader, or slight HV sparks.


Check the grounding and measure whether the ground leader meets relative requirements (resistance to earth should be no higher than 5W). Modification to grounded leader should be executed to make it meet relative requirements.

Check whether the network connection is loose or there is defective connection of the press buttons on the control panel.

Whether there is any strong e-magnetic disturbance near the machine.

Check whether screen protection or energy saving (such as system sleep or HD turned off, etc.) had been set. If yes, cancel this setup and change it into “never”.

If it had been set “output forbidden” or engraving type or other parameters had not been set in the new Yueming software.

Check whether there is any error such as overlap, non-closure or slipping, and other in original graphics. Correct the errors in graphics and then test output again.

If Wentai software is employed for output, check if the calculation of track is normal. Register or install the Wentai software again, even the whole system if necessary.

If there is no such error in other output format, then the graphics is problematic. Re-output or redo it is necessary.

Check whether there is spark from the laser diode or laser power supply.

If the problem remains, replace the main board and test the computer.

K.Abnormal reset, slipper or beam shaking or wall impact when turn on the machine

Failure: wrong direction of reset when turn on the machine, slipper or beam shaking, wall impact of the slipper or the ridge beam when reset; clear buzz when the motor is on.

Causes of this failure: this kind of failures is caused mainly by wrong parameter setup or wrong wire connection after replacement of main board, motor drivers or reconnection of wires; another possible reason is loose wire connection on machine, sensor, motor drivers and drivers.


If abnormal reset occurs after replacement of main board or drivers, parameters setup should be checked first. This abnormal reset problem can be resolved through modification of the parameters on the main board.

Turn off the machine and push the slipper and beams with hand to fell the resistance. Any resistor should be cleared and the firmness of the tension wheel on the left side should be checked.

Check whether any of the synchronizing belt, the laser head, the blow pipe, or the towline is locked.

Check whether there is too much dirt on the lead rail to block the slipper. Clean and lubricate the slipper block.

Push the slipper to check whether there is stridulation or shaking. If the gap of the slipper block is too wide, it should be replaced.

Check whether the beam is seriously deflective. Each of the deviation of both sides should be no more than 2 MM. Check whether the wheel of the support base is problematic and whether it can be smoothly pushed.

Check whether the wire connection between motor and drivers is good.

Disassemble the machine and find out the axis, of the slipper or the beam, on which the shaking is. Disconnect the power supply of one axis to test the motor and the drivers of the other one to check whether there is any failure. These two tests are alternative and can be used to find out whether the motor or the drivers is problematic.

Machines with resistor array want resistance measurement. If the resistance value is not correct, it should be replaced.

The direction of reset is right but the slipper or the beam cannot stop at the end and impact on the machine. The parameters of the main board should be checked to find out is there is any error. Check whether the sensor or its wire is broken or whether the position of the magnet is right.

Whether there is too much dust on the sensor (photoelectric sensor).

When old model machines and YM machines fail to reset, pay attention to whether there is defective connection or open circuit with the 18-core data cable. Re-insert or replace the cable.

If the problem remains, the main board may be problematic and needs replacement.