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  1. #1
    Join Date
    Mar 2013
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    126

    K40 laser quit firing (upgraded)

    Hi All. My laser tube quit firing today. I had been ok earlier then nothing. I have pushed the button on the power supply to make it manually fire and it would not. When i was checking connections and pulled the machine out i pulled the ground wire off the back. could i have burnt up the power supply by not having a good ground(if it was lose). Any help would be great!

  2. #2
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    the fan is running in the power supply. Not sure if the light should be on or not. when the machine comes on it flashes red for a sec then goes out. When i push the test button it does not light.

  3. #3
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    Ok i got the light back on. When i push the test button the light gets brighter but still not getting any beam

  4. #4
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    what would be the power measurement on the backside of the power supply? should i try to test it at the laser to see if it has a output? or will it just shock the crap out of me lol ?

  5. #5
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    ok i have power at one end of the tube but nothing at the other end. does this mean i need a tube?

  6. #6
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    i do have like 2v coming out the other end if i am reading it right

  7. #7
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    I am sure its safe to say i need a new tube have ordered one. will find out in a few days when it comes in.

  8. #8
    Join Date
    Nov 2014
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    284

    Re: K40 laser quit firing (upgraded)

    Scott I just got done last week troubleshooting my new laser for an intermittent problem but mine was where the beam was coming on and staying on some of the time. Dangerous and annoying. I worked as an electronics technician all my life and hate intermittents but it got me to look over how these things operate so maybe can help you a bit. First of all the high voltage end of the tube and the power supply can shock the hell out of you and maybe even kill you. If you don't know what you are doing leave that stuff alone!!! I reversed engineered my supply and came up with what is involved in the trigger circuit to solve my problem but the results give some possible solutions to a path for troubleshooting basic problems.

    First is to define the path and I can only describe my unit which has basically two components in the electronics bay: first is the all-in-one power supply: http://en.jnmydy.com/products_detail...c3343a3b6.html that is what mine has and what my discussion will be about. Also in the bay is the electronics/program board but that is a separate system that only gives a fire signal via the "L" connection to the power supply. (my unit also has a wall wort to supply power to a built in light bulb but that has nothing to do with the laser as such). On the lid is the "test" switch which supplies a ground to the K+ lead on the power supply to fire the laser like the L pin does.

    So on the power supply normal trigger indications: "grounding" either the L lead or the K+ lead pins turns on the laser beam! You can check that with a common voltmeter connected between ground (- voltmeter lead) and either the K+ or the L inputs to the supply (+voltmeter lead). Let's just check the K+ lead first. With your voltmeter set on say 20 vdc scale you should measure 5 vdc (negative lead on ground pin and positive lead on K+ pin). Now when you push the "test" switch the meter indication should go to zero (or under .6 vdc) and the laser tube should fire. If you have the current turned off on the tube (000 on my digital control panel) it shouldn't fire but the red LED under the test button should illuminate steady on. Those are the normal indications and I think isolate the problems to the high voltage section of the supply or the tube. .

    If your K+ voltage stays at 5 volts when you push the test switch then check the control panel connector (not plugged properly, bent pins, or maybe the switch is defective or improperly soldered etc.) or you can just jumper across the K+ and K- (K- is just another ground connection) pins with a wire and the laser should fire. If so there is a problem in the control panel or it's wires.

    If your K+ pin is always at zero (and the laser tube stays "on", dangerous), then disconnect both the K+ lead connector and the L connector (it is the right hand connector that feeds 5 and 24 vdc to the software board. Recheck the power supply pins on both connectors and confirm voltages as they are marked for 5 vdc, 24 vdc and 5 vdc on K+ and L pins. Now wiring a jumper across K+ and K- should fire the laser. If not you have either a bad supply or tube. The problem is not in the software board. or the test switch.

    As a side note on this the laser the "on" function has a safety line in series with these trigger lines. It is the D+ D- connector and it must have continuity for the laser program to function. I can't remember if it inhibits the test switch but it sticks in my mind that it doesn't so watch out! Mine is jumpered but it would be one more thing to check or bypass for testing purposes. While on this subject I found some poor connections on the wiring (yes that is common) and even before operating the unit you might save some grief by doing housekeeping on all of the connectors. I will be adding a water and lid switch in series with the D+, D- pins eventually.

    OK the above tests check good for the power supply input. How do you check the high voltage? I didn't have a high voltage problem but later I'll try to come up with something maybe based on a car spark checker or perhaps a spark plug. This would involve a very brief push on the test button to confirm say a 1/8" spark.I don't know yet without doing some engineering. I do know the biggest danger (to the power supply) should be from operating it (high voltage section) "unloaded" (disconnected from the tube). The voltage would build to an unacceptable level and possibly spark back into the low voltage (5 and 24 vdc) electronics of the supply wiping it out.

    One more thing about the high voltage: It requires a complete circuit on the ground end of the tube to render the return wire safe. On mine the output end of the tube is run from the tube to the big green resistor and from there to ground. If any part of that circuit opens or becomes disconnected then the return wire goes to full high voltage!!! Always treat even the ground return wire and resistor as if it could kill you! Don't measure or touch any of that stuff!!

    If you insist, you can purchase high voltage voltmeters. They have a Frankenstein look to them with long handles and circles of plastic to protect you from the 10-20,000 volts. I have an old Heathkit HV meter model IM-5210 (find a picture on line) and those may be available on ebay? Even if you get one of that type I would still stand in tennis shoes on a 5 gallon dry plastic bucket with one hand behind my back before using it :-) Don't let any part of your body come anywhere near the case or ground (or anything but the bucket and the HV voltmeter handle) DO NOT TRY A REGULAR VOLTMETER! The voltage will arc right through the leads and insulation and if it doesn't kill you it will surely fry any meter you may use.

    Hope this was helpful.

  9. #9
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    well i know its not a tube problem. got the new one in and hooked everything back up and still dont have a beam. so i am going to check all my connections over again and try to test the leads as you suggested. In did not know that the tube paked that much juice. I was messing with the wires trying to test the voltage. Would it be safe to assume since i didnt get shocked that it was the power supply?

  10. #10
    Join Date
    Nov 2014
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    284

    Re: K40 laser quit firing (upgraded)

    Yep that was my thought exactly. Unfortunately the tubes don't apparently last in storage. If you have a voltmeter test all the input and output pins on the low voltage side. On mine the high voltage is in the back and all the low voltage is in the front. Are you sure the laser is not firing? It could be missing the mirrors and you might not know it. Place a piece of paper directly between the laser output and the first mirror and see if it burns a hole in the paper. Can you describe the power supply and it's pin outs? Is it an all-in-one like I gave the link to? I forgot to mention the power setting. You do have it "on" correct? I didn't see you mention that. On mine there are some up/down arrow buttons and a digital read out in % (I think). I believe the older ones use an ammeter so directly readout tube input current in milliamps and a variable resistor to set power.

  11. #11
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    mine was a k40 that i did a up grade on it was working fine when i started out that day and quit between jobs. the power supply fan is on, but there is no light in the tube when i test fire it. most times you can see it light up

  12. #12
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    Nov 2014
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    284

    Re: K40 laser quit firing (upgraded)

    Yeah I've never looked at mine while it's on. I have seen youtube video's of them firing and I know they have a glow discharge type thing in them while running. One thing I left out of the troubleshooting post was the possibility the power control % circuit was broken. Assuming you have a meter is it moving up scale when you push the test button? I think I remember someone critiquing these things and saying the meter was in series with the high voltage ground which if the meter circuit opened would place high voltage on the panel. Don't take that to the bank, it was just something I read somewhere but I would still watch out!
    I've been trying to think of a good DIY home getto rigged way to test for the presence of high voltage. I don't remember my physics exactly but how about a piece of styrofoam tied to a string suspended from a piece of plastic? I think it should be attracted or repelled from something with high voltage on it? Stop the presses! I went and tried it on my laser. A 6-7 inch piece of sewing thread with a packing peanut tied on the end and suspend it about an inch from the insulated HV wire in the electronics bay and at thirty % power it and hit "test" button and the peanut moves right over and sticks to the wire! I wish to call this the "Lucius Gale" method in honor of my GG Grandfather. ;-) This is a relatively safe method to test for the presence of sufficient voltage to fire the tube! Make sure you use a dry string!

  13. #13
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    Nov 2014
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    284

    Re: K40 laser quit firing (upgraded)

    I gave this a little thought about what the presence of high voltage with no fire from the tube would mean. If your HV test shows high voltage and since you have already replaced the tube, the next thing could be an open ground return, the wire that goes back to the big green resistor. You should not see the peanut deflect when near the ground line or the resistor. If you do it means it has HV on it because the wire, resistor or something in series with it is open (broken, cut, disconnected, bad connection etc. The peanut should not see HV anywhere on that line.

  14. #14
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    when i rebuilt my laser the green thing got removed , i have checked all my connections think i am just going to buy another power supply and hope for the best. or take this one to a shop and have them see if it tests ok

  15. #15
    Join Date
    Jan 2015
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    9

    Re: K40 laser quit firing (upgraded)

    Attachment 266404 Hello, excellent info here. I included schematic of my power supply.... Letters not the same as what you are talking about. I'm having same problem, everything works but no power to tube. Bypassesd flow switch, no other "off" switches on machine (50 watt Chinese)... Test button does nothing, fuse OK in power supply. Tube looks fine, did styrofoam test, nothing happens on red or return wires. So you talk about the K+ lead, I have nothing labeled as such. On mine I tested L and had 4.96 volts, hit test, drops near 0... Then went to IN, which I thought must be the same as K because all the rest are going to ground. Tested that showed 3.56 volts and when I hit test, it actually went up to almost 4. I'm a poor artist and can't afford to buy parts I might not need.... (can't afford one's I do for that matter)...but need the machine working. So it looks like I have at least some power going in. Green light stays on, fan works.... But it does not look like anything is going out... Would this narrow it down to the power supply?

  16. #16
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    Nov 2014
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    284

    Re: K40 laser quit firing (upgraded)

    Quote Originally Posted by jeff4freedom View Post
    Attachment 266404 Hello, excellent info here. I included schematic of my power supply.... Letters not the same as what you are talking about. I'm having same problem, everything works but no power to tube. Bypassesd flow switch, no other "off" switches on machine (50 watt Chinese)... Test button does nothing, fuse OK in power supply. Tube looks fine, did styrofoam test, nothing happens on red or return wires. So you talk about the K+ lead, I have nothing labeled as such. On mine I tested L and had 4.96 volts, hit test, drops near 0... Then went to IN, which I thought must be the same as K because all the rest are going to ground. Tested that showed 3.56 volts and when I hit test, it actually went up to almost 4. I'm a poor artist and can't afford to buy parts I might not need.... (can't afford one's I do for that matter)...but need the machine working. So it looks like I have at least some power going in. Green light stays on, fan works.... But it does not look like anything is going out... Would this narrow it down to the power supply?
    Sounds like a power supply. Your test indications are correct (at least for mine) as 5 volts is the "off" state and 0 volts is "fire" so the switch is working correctly. I don't have any safety interlocks on mine so ymmv. . The "in" line appears to be the laser power control line. Note in your schematic the "swinger" or middle connection to the potentiometer moves from zero volts (gnd side) to 5 volts (other end) so it can be adjusted anywhere from 0 to 5 volts and you are getting a high power setting indication on the "in" terminal at 4 volts. So the external power control is set at 80% of maximum power, the test switch is connecting the "L"line to ground or fire position but the high voltage side of the supply is not putting out any or enough voltage to even move the peanut so barring a short circuit on the high voltage line, I would vote 99% confidence sure it's the high voltage section of the power supply. If it was an open milliammeter the peanut would still detect high voltage (peanut test).

  17. #17
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    I would say the same. You can all ways take the power supply to a tv repair shop and have them look at it.That is what I ended up doing.

  18. #18
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    Nov 2014
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    284

    Re: K40 laser quit firing (upgraded)

    Hey Scott,after you got yours running did you try the "Lucius Gale" peanut/string test on yours to confirm it works on your 's like it did mine?
    edit Oh and what did the tv repair shop say was wrong or did they just confirm you needed a new one?
    edit Yet again .Be sure and connect your spare tube up to high voltage and fire it every couple of weeks or so if you want it to remain viable as a spare.... Or so I've heard on the internet. Again ymmv since I don't know the actual theory behind that. Everyone agrees they have a shelf life.

  19. #19
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    Jan 2015
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    9

    Re: K40 laser quit firing (upgraded)

    Thanks

  20. #20
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    Mar 2013
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    126

    Re: K40 laser quit firing (upgraded)

    they told me what it was ... but drawing a blank right now. i think it was the voltage regulator. I never have done the peanut test.. I just got me a 3d printer going to make new x y axis and build another laser here soon!

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