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Thread: Lexel 95 and the quest for the missing tube voltage

  1. #1
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    Default Lexel 95 and the quest for the missing tube voltage

    Picked up this system today (ebay grab) and spent most of the evening getting things set up.

    3 HP motor as a rotary phase converter, electrical disconnect box, dryer plug

    Everything seemed to be working fine, the phase and fuse neons and interlocks all lit on the psu, the "laser start" latches in properly and the cathode heats. But once it's all ready to go, hitting the ignite button only results in some relays clicking and nothing from the tube.

    The voltage meter on the psu reports nothing on the reg 50v and 300v settings, but 300vac registers a proper reading.

    The tube is pristine (based on the hours and manufacture date) so I really hope I can get this one going.

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    Full 20mb picture pack showing multiple angles of the psu and head here - http://dl.dropbox.com/u/1181169/LexelImgs.rar
    http://dl.dropbox.com/u/1181169/LexelImgs.zip (if you don't have winrar)

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    'sup, Dude...

    Quote Originally Posted by MarioMaster View Post
    ...But once it's all ready to go, hitting the ignite button only results in some relays clicking and nothing from the tube.
    ...little-more detail; please define "nothing"... (any plasma-glow, at-all? I assume-not if you get no current readings off the meter, but, gotta ask...) If NOT: Have you 'verified gas-integrity', with a portable-tesla or neon-tube tester? (remember the little mini-one I used at your place when I was picking-up that old-skool Argon, for Sir Hess? If-not, and you need a 'walk-thru' on how-to, lemme know... Also, I will assume that "all interlocks" includes Water flow/pressure: 'OK', yes?

    Let's 'start here'.. if I 'trail-off', I am sure Sir Mixedgas will chime-in, asap...

    peace...
    j
    ....and armed only with his trusty 21 Zorgawatt KTiOPO4...

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    I know this is simple, but I spent countless hours diagnosing problems that weren't really there on mine:

    Is it tapped correctly?

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    Is it tapped correctly?[/QUOTE]

    That is the big one. I'll dig out a tap chart.

    Don't try to run it till we set the cathode and buck boost taps, OK?

    Also the mercury hour meters are about worthless, we have no idea until we run it up. The rust on the head fittings is a giveaway that she's old.

    If we have to troubleshoot, do you have a transistor tester? Or a transistor test function on your voltmeter? A small variable voltage power supply?

    These are easy to fix, but there is a series of steps to follow before you assume she's dead. Its not always a "hook up and go", and what the meter says and what it means are a bit different when the tube is off vs on.

    One other thing I need to know, is your meter true RMS or normal? If its true RMS it WILL say so on the front.

    Do you own a "ampclamp" ie a clamp on AC amp meter?


    3 HP would be 2250 watts if perfect physics existed. In reality you may not have enough motor as you have a 6 kilowatt laser.This is tricky because it will pull down the cathode voltage once lit, and this is bad. You may have enough "peak" open circuit voltage, and yet not enough when it loads up. This will be a bit tricky as the testing is based on numbers for pure three phase. The buck boost concept works with "real power" not apparent power. The front end of the PSU is designed for balanced currents, it may not "like" trying to draw power through mostly one phase of the rectifier string.

    Can you bring it to SELEM? Can you get access to standard 208 3 phase just for testing?

    Steve
    Last edited by mixedgas; 08-03-2010 at 05:13.
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    Thanks for the responses everyone.

    Quote Originally Posted by dsli_jon View Post
    'sup, Dude...



    ...little-more detail; please define "nothing"... (any plasma-glow, at-all? I assume-not if you get no current readings off the meter, but, gotta ask...) If NOT: Have you 'verified gas-integrity', with a portable-tesla or neon-tube tester? (remember the little mini-one I used at your place when I was picking-up that old-skool Argon, for Sir Hess? If-not, and you need a 'walk-thru' on how-to, lemme know... Also, I will assume that "all interlocks" includes Water flow/pressure: 'OK', yes?

    Let's 'start here'.. if I 'trail-off', I am sure Sir Mixedgas will chime-in, asap...

    peace...
    j
    There was no plasma glow at all, and yes - all the interlocks were lit, I grabbed the proper garden hose fittings at the local hardware store on the way home from picking it up. I don't have an oudin coil, but I don't think I'd be able to see anything anyway - the tube doesn't have any exposed glass and the last thing I want to do is pull off the brewster window covers.



    Quote Originally Posted by mixedgas View Post
    Is it tapped correctly?
    That is the big one. I'll dig out a tap chart.
    thanks
    Don't try to run it till we set the cathode and buck boost taps, OK?
    got it
    Also the mercury hour meters are about worthless, we have no idea until we run it up. The rust on the head fittings is a giveaway that she's old.

    If we have to troubleshoot, do you have a transistor tester? Or a transistor test function on your voltmeter? A small variable voltage power supply?
    no, yes, yes

    These are easy to fix, but there is a series of steps to follow before you assume she's dead. Its not always a "hook up and go", and what the meter says and what it means are a bit different when the tube is off vs on.

    One other thing I need to know, is your meter true RMS or normal? If its true RMS it WILL say so on the front.
    my Fluke 902 is true RMS

    Do you own a "ampclamp" ie a clamp on AC amp meter?
    yup, the Fluke

    3 HP would be 2250 watts if perfect physics existed. In reality you may not have enough motor as you have a 6 kilowatt laser.This is tricky because it will pull down the cathode voltage once lit, and this is bad. You may have enough "peak" open circuit voltage, and yet not enough when it loads up. This will be a bit tricky as the testing is based on numbers for pure three phase. The buck boost concept works with "real power" not apparent power. The front end of the PSU is designed for balanced currents, it may not "like" trying to draw power through mostly one phase of the rectifier string.

    I know it's probably not big enough, it's the only 3 phase motor I have (dug it out of a junkyard) I was hoping to just sustain a low idle current in the laser to make me happy until I could get access to real 3 phase power. I have access to 208 3 phase @ 20 amps per leg in my dorm room, and probably more if I can convince a professor to lend me some time in a lab or something.

    Can you bring it to SELEM? Can you get access to standard 208 3 phase just for testing?

    I'd love to go to SELEM but transportation is an issue - I go back to school on August 16th and it would be a huge fuel cost to drive to NC.

    Steve[/QUOTE]
    Last edited by MarioMaster; 08-03-2010 at 07:41.

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    OK, because you are not instrumentation blind, which is a VERY good thing, we have a chance. As long as you understand three things.

    Your first priority is your education, if a Lexel has good gas pressure, they stay at good gas pressure when not being ran. Ie it has a very long shelf life. Your in no hurry. Keep your grades up.

    Two, you must at all costs not take the cathode outside of its operating temperature range. Especially too low. When processed at the factory they do not greatly overdrive the cathode, and heating it too much may change its surface condition. Too low, and tungsten has a transition temperature range where it sags like butter. Your aiming for 1180 C, a warm, orangish white glow. A red, weak glow is bad, the tungsten softens if too cold. The cathode transformer gets its power off a 100VAC tap on the buck boost, hence if the currents in the buck boost are unbalanced, the cathode cools off.

    The Ampclamp is very good news because you can monitor the cathode fairly precisely.especially if you can borrow a second voltmeter.

    Three, we have to watch the phase balance. If you look at the passbank, there are six rectifiers, and they like to have balanced currents. They are way overated diodes, but asking one pair to take the whole load is a very bad idea, and while the tube will wink out, the filter capacitor, which is sized for 360 Hertz harmonics, tends to be grossely undersized for 120 Hz harmonics and will pop from the excessive currents.
    While easy to repair, popping the rectfiers and caps is a pain in the neck, because it immediately pops the big fuses, which cost far, far more then any other part of the unit save the optics and plasma tube.

    The amp clamp will be a great help. Its a stop, do not pass go, do not collect 200$ thing if you did not have one

    Do you have balance caps on your phase converter, or is this the external starting motor, unbalanced, freewheeling kind?

    Steve
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    Lightbulb

    Hey MM -

    Quote Originally Posted by MarioMaster View Post
    There was no plasma glow at all, and yes - all the interlocks were lit, I grabbed the proper garden hose fittings at the local hardware store on the way home from picking it up.
    Right on... Well, you know the drill - you start from the 'simplest things first'...

    Quote Originally Posted by MarioMaster View Post
    I don't have an oudin coil, but I don't think I'd be able to see anything anyway - the tube doesn't have any exposed glass and the last thing I want to do is pull off the brewster window covers.
    Don't need-to - and you don't even need to 'wait' to be sure your power is correct for the load / operation (...but Steve is 'The Man', isn't he? you can test for gas-integrity with everything powered OFF, simply pop the HR and hit one of the cathode lugs while 'looking down its keister' (though, you may need to 'search around' a bit for it to find the 'path home'...) ...and you could possibly get it to even-'go thru' the heat-shrink-tube (?) dust-cover, there, to the glass stem... (just stay-back away from the END of the brewster windo / and 'seal'... )

    ...And at $30. ie: http://cgi.ebay.com/NEON-TUBE-TESTER...-/190425473636... one of these little puppies can save you a *lot* of time and fussing around, up-front , when you get a new head-in... even this little-model, while certainly not the 'most powerful', will light-up (good-enough) I-90s, Lexxies, 168s - even a 171!

    IMO, Just a really 'good bit of kit' (like a true-RMS DPM / ampclamp, etc) for any Ion-wrangler, such as yerself...
    ...I mean, if she's up to air, what's the 'point' of all the rest of the testing, right?

    EDIT: Alt-idea: Call-up your local Neon-shop (or Sign-shop / Tuner-Shop that also does custom neon), and 'nicely' explain you need to 'test a laser tube' and 'would they let you 'borrow' a neon-tube tester for a couple hours?'... you could offer to leave a small, refundable 'security deposit' or offer a small, 'reasonable rental' fee (like $20. or something, tops...)
    ...this way, you can test it 'now' rather than wait for some eBay shipper, etc, and w/o having-to drag the head down to the neon-shop...

    Anyhoo, just 'FWIW'...
    peace...
    j
    Last edited by dsli_jon; 08-03-2010 at 17:44. Reason: alt-idea
    ....and armed only with his trusty 21 Zorgawatt KTiOPO4...

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    Thanks for the suggestions - I disconnected the anode wire from the inductor in the head as something was causing about a 5 megohm resistance across the tube. Then hit it with my spare SP-127 HeNe brick. I was greeted with some reddish flashes from the mirror


    Steve - The phase converter I had set up was using 50uF of run capacitors (all I had laying around) from L1 to L3.

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    Ok, this assumes 3 phase Wye service, God only knows on your phase converter.
    We usually just use this as a guide, there are variations based on tube condition and power quality. Since you wont see the true voltage unloaded.... Your guess is as good as mine.


    Generic 95

    measurements are normal voltmeter, NOT RMS.

    Open circuit, tube not lit, tube voltage should be about 300 VDC.


    There should be a plastic piece forcing you to move all three wires at a time.
    Buck is orange to left
    Boost is blue to the left


    measured voltage,
    230-245 orange on x4,y4,z4 blue on x1,y1,z1 max buck
    220-230 orange on x3,y3,z3 blue on x1,y1,z1 medium buck
    212-220 orange on x2,y2,z2 blue on x1,y1,z mild buck
    204-212 orange on x1,y1,z1 blue on x1,y1,z1 neutral, (still powers cathode chain.)
    196-204 orange on x1,y1,z1, blue on x2,y2, z2 mild boost
    190-196 orange on x1,y1,z1 blue on x2,y2,z2 medium boost
    185-190 orange on x1,y1,z1, blue on x4,y4,z4 max boost


    Cathode switch, if cathode transformer AC is less then 108 or more then 135 at the test points, your screwed or you need to retap the buck boost.

    typical for a 95 S10 settings
    less then 114VAC set to "A"
    at 114 to 124VAC set to "B"
    At greater then 124, set to "C"


    Your goals are:

    I:
    .As close to 280V dc across the magnet as possible when lit

    II:
    ...Passbank voltage 3- to 50 volts in the green range (lower current = higher passbank V) Passbank V is a DIRECT measure of stress on the passbank, and the transistors will start popping for sure at 70V. If energy is NOT going into the tube, its turning to heat in the passbank! So you adjust the buck boost so that the stress on the passbank is minimal at LOW tube currents.

    III:

    Cathode conditions: 3.2 VAC before plasma.

    Imax: 95-2 = 29A 95-3 = 32 amps 95-4 = 34 amps

    If the tube is healthy and gas pressure is good, you should see cathode AC amps increase on the amp clamp as more heat is needed when the plasma starts and your running at test current (ie 20-30 amps) Measure when stable, it fluctuates wildly at start for say 5 seconds. Electrons leaving the cathode physically cool it, so it needs to draw more current to be stable. If gas pressure is too LOW, the cathode current will DIP as the plasma warms up. Again, if you can only source 9 amps to the tube, because of your phase converter, this is meaningless.

    The cathode current will also dip if your phase converter can not keep up with power demand, so you must watch for this.

    Itube min should be about 6-8 amps, running below this for any length of time, I would not do on a phase converter.

    overcurrent trip is set at 38-39 amps at the factory.

    For a properly peaked 95, I'm guessing lasing threshold for 488 only to be 14-16 amps, give or take.

    Vtube at test current is about 235-240V give or take. Higher is better, tube voltage falls with decreasing pressure as the tube ages. It can vary widely at low currents, and is somewhat proportional to tube current.

    At full power you would be drawing around 20 amps per phase.

    At start, run in current mode, turn the knob full clockwise, and then back off 1/4 turn. disable auto start/ignite if installed. It wont hurt it if it can't reach max power.

    When I get my scanner's driver installed on the inet computer, I will scan you a schematic. Past experience says it costs about 40$ just to copy the manual.

    Dont expect lasing, be happy with plasma. If it does not lase, and you have a decent percentage of tube current, mark the position of the vertical knob on the rear and gently and slowly move it 1/8th of a turn in either direction. That usually does it, but since you have no idea how it was handled before you got it, I would NOT expect lasing. You really want to do lasing on a up end power source.

    I will pray that this works for you.

    My cell# has changed, PM me if you need to talk.

    In fact, I pmed you with the number so I can walk you through a passbank check before you try to run again.

    Steve
    Last edited by mixedgas; 08-04-2010 at 08:55.
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    Thanks again for all the great information Steve. I went over the system again earlier today and about smacked myself when I found the problem. Transformer was set to max buck as my line voltage at home was pretty high (almost 250v), cathode voltage was still a bit high at 3.4vac so I'll definitely want to decrease the voltage to the cathode transformer next time I try to power it up.

    I went to the head and then checked for tube voltage, found nothing - went to the psu and checked for tube voltage, found nothing. Checked the filtering capacitor, found nothing. So all this finally gave me the idea to check the main rectifier diodes.

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