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Thread: fanuc ts20 resistor burns at startup

  1. #1

    Default fanuc ts20 resistor burns at startup

    we have a problem with our fanuc spindle drive A06B-6044-H011

    when we turn on the main switch the resistor r1 (3k+4ohm, big green one on top) burns out on the 4 ohm side when we put the main switch on in the 4 ohm side of the resistor there is 300v on (on a same other machine we get there 2v on startup) screen is not powerd on yet

    does anybody have a solution for that

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  2. #2


    Dear Sir,
    The resistance is burnt out due to Failure of Power regulator Circuit I mean the Transistor/ IGBT module inside the servo amplifier , Check the diode Module Transistor Module and Regenerative Circuit of the Spindle Drive Unit , Please assure the capacitors are discharge before attempt to repair. If you need any other help please free to communicate over

  3. #3


    the regen transistor is usually tagged 'Q1' on the little white identification decal inside the drive, see if any terminals on it are shorted (be sure to let the caps bleed off/check residual DC buss voltage before mucking around in there!). if Q1 isnt shorted, either the firing circuit is screwed up on the top card, or your incoming voltage is too high. you can cross reference to a higher current rated transistor that will fit- we upp from a 30 amp to 75 amp on ours(bit newer model than your 6044), suprisingly had to make a aluminum 'shim' to match the height so the 'board with a million screws' fit flush...funny the bigger rated transistor was like 1/8" thinner, think they only cost about 20 bucks, never blew another one.

    Fanucs will go into regen at right around 242 incoming to the drive, even if they are just sitting there. if youre anywhere near that, you can try moving primary taps up a notch on your isolation transformer(if it has a primary trans) to reduce the secondary...we usually tap our transformers at 510 to run on 480 service, gives a secondary closer to 220. watch your capacitor bank in your sub is functioning correctly too- we had a bad VAR controller holding caps on during lightly loaded weekends, 480 was getting kicked up to near 520, baked a bunch of regen circuits...Power companies ding you hard for pushing a leading power factor too...

    if the shop is messy with chips/air nozzle-happy operators, might want to shut down/open up the machines isolation transfomer, make sure no chips inside...Ive seen a few times where chips got into windings, shorting primary turns at the taps, causing boosted secondary voltage on a leg or two.

    Also if youve got any BIG 4 quadrant regen loads on the same busway(especially if youre on a smaller service) watch voltage during braking of other equipment- it can really surge up there...if it does, try increasing decel rates on that equipment to reduce the regen load backfeeding the buss.

    Dont ever let a fanuc amp sit at over 240volts input, they will begin to roast steadily at 242.

    we have had machines come in with isolation transformers without the usual 5% taps, actually had to replace the transformers as there was no way to drop the secondary down to the safer 200~220 range. Shops on low power 208Y120 have it made for Asian equipment, but if youre on 240 or 480 delta, taps are a must have item...without taps, Q1s/firing cards/resistors self destruct easily...

    Suggest any isolation transformers are delta-delta too- we had one HUGE Kitako 4 spindle/8 axis lathe that was scrapped after a lightning strike- only machine in the shop with wye-wye type transformer, the wye windings apparently let something other machines in the shop were affected, but it blew both spindle drives, all 8 axis drives, both 6TC power supplies, 4 mother boards, and who knows what else...they literally hauled it to the scrapyard.

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