Attempting to repair a Servo Type 100 power feed Circuit Board
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    Unhappy Attempting to repair a Servo Type 100 power feed Circuit Board

    Hello everyone

    I have a friend who is an machinist and owns an old Bridgeport mill with an even older Servo Type 100 power feed.

    He never installed a limit switch on his power feed and then one day, he turned on the power feed to maximum speed by accident and the mill hit the end, apparently killing the servo because it released some magic smoke.

    Since Type 100 circuit boards are pretty much impossible to find nowadays and the type 150 boards are over $100 plus tax and shipping (like this one or this one), I wanted to attempt to repair the damaged board myself.

    I'm not an electronics expert but I do have a lot of experience. This is what I have found so far:

    When I plugged in the 110v cable of the power feed, the breaker would trip instantly. I opened the Servo unit, I noticed that the circuit board had short-circuited traces right where the 110v lines come in. I repaired the damaged traces and then started diagnosing components. All Varistors are fine (open, not shorted) and I found that the Bridge Rectifier diodes were dead, they had continuity on both directions. I replaced all 5 Diodes (400v 6A) found in the Bridge Rectifier area, replaced a blown 16v capacitor, tested all resistors and all of them appear to be fine.

    Now, when I plug the 110v cable the breaker does not trip anymore. The circuit board is being powered, the bridge rectifier appears to be doing its job, but the servo motor doesn't spin. The coil of the motor gets warm which tells me its getting power, but it just doesn't spin. I tested the Potentiometer wiring and looks fine, and the Forward/Reverse toggle is fine as well, carbon brushes are fine but I can't find what else could be dead on the circuit board or any other place of the power feed. Any tips/help will be appreciated.


    Here's a link to my Onedrive with some Pictures I grabbed from the board:

    https://1drv.ms/f/s!Asv5yaQakrNSiMQBsZVmAgEDPQk-SA

    Olivier

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    The last one I repaired had blown thyristors (from memory they are isolated tab and maybe GTO - gate turn off -sorry can;t remember exact type )

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    Quote Originally Posted by Billtodd View Post
    The last one I repaired had blown thyristors (from memory they are isolated tab and maybe GTO - gate turn off -sorry can;t remember exact type )
    Thanks for the reply.

    Are these the components you are talking about?

    20190529_100818.jpg

    I have been suspecting about them but wasn't sure if they were Transistors, Mosfets, Thyristors, TRIACs...
    They don't have any visible damage, I tried googling them but could not find anything.

    They have written: S99 MEX F6 and have a logo that looks like a curved T.

    The link I put on my previous post have several pictures of the servo board, maybe you could spot something I missed?

    Regards
    Attached Thumbnails Attached Thumbnails 20190526_120716.jpg  

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    Just found that this curved T is the logo of a company named "Teccor" which was acquired by Littelfuse on 2003, now just need to find the specs of these thyristors (assuming that's what they are)

    When I look at other similar boards like the ASONG from this topic, they seem to be SCRs rated for 8A 600v approx. I assume I could just replace them with anything similar

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    Managed to find my scribbled circuit diagram : (must be your lucky day)

    The thyristors are iso tab sensitive gate types , not the typical types, but most electronic retailers (digikey farnell) should have something suitable )
    Attached Thumbnails Attached Thumbnails align-power-feed-circuit.jpg  

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    The Servo 100 and Servo 150 are basically identical. Get a replacement 150 circuit board and pop it in.

    Jon

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    Quote Originally Posted by Billtodd View Post
    Managed to find my scribbled circuit diagram : (must be your lucky day)

    The thyristors are iso tab sensitive gate types , not the typical types, but most electronic retailers (digikey farnell) should have something suitable )
    That's awesome, thanks a lot for uploading it. I have no clue of what an "iso tab sensitive gate" is but I'll look for options. Also, your drawing seems to be for an Align jc-10a power feed, you sure its the right one?


    Quote Originally Posted by HWElecRepair View Post
    The Servo 100 and Servo 150 are basically identical. Get a replacement 150 circuit board and pop it in.

    Jon
    I'm a cheap ass, I'm trying to save those $120 and avoid creating some electronic waste. Plus I love electronic challenges.

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    in most transistors and SCRs the middle pin is connected to the tab electrically so the mounting tab has to be careful ly isolated to prevent shorts. The iso tab package isolates the middle pin allowing the thing to be bolted down direct ly.

    Sensitive gate means the device need far less current into the gate, to make it switch ,than a typical scr . The ones i fitted were 0.2mA

    The circuit may be different, you'll need to trace to compare . My guess though is that the fix SCRs willthe thing ;-)

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    Quote Originally Posted by Billtodd View Post
    in most transistors and SCRs the middle pin is connected to the tab electrically so the mounting tab has to be careful ly isolated to prevent shorts. The iso tab package isolates the middle pin allowing the thing to be bolted down direct ly.

    Sensitive gate means the device need far less current into the gate, to make it switch ,than a typical scr . The ones i fitted were 0.2mA

    The circuit may be different, you'll need to trace to compare . My guess though is that the fix SCRs willthe thing ;-)
    Makes sense, thank you. I just measured continuity between the middle pin and the TAB and they are isolated. Thanks for the electronics lesson

    I'm looking for SCRs manufactured by Littlefuse and apparently the only one they have that supports 8~10amps at 400v is this one:

    S4010LS2TP
    SCR 400V 10A Sensitive Gate Through Hole TO-220AB-L
    https://www.digikey.com/products/en?...4010LS2TP&v=18

    Does it look like a good fit? I know the brand doesn't matter at all but just wanted to see what Littlefuse had to offer, since they appear to manufacture the original Thyristors for this circuit board.

    When I look in Amazon for "sensitive gate scr" I get some bizarre results, like this Thyristor that also claims to be a TRIAC (my understanding is that they are similar, but different components)

    https://www.amazon.com/TOOGOO-Thyris...s%2C434&sr=8-4

    I'll go buy a couple of new Thyristors this weekend and try them. Best case scenario: I fix the board and you earn a 6-pack of the beer of your preference. Worst case scenario: The board burst in flames and I'll go buy a new Servo 150 board.

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    that looks like the same spec as the ones i used (200uA =0.2mA)

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    I could not find these SCRs here in Costa Rica (I found some, but they were not ISO tab), so I ended up buying them from Digikey. Should arrive in about a week.

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    Update: I finally got the new SCRs and installed them on the servo board, but unfortunately, the issue remains.
    I really wanted to fix this board but I don't think I can spend any more time troubleshooting, so I'll just tell me friend to grow his biceps and drive his mill by hand

    Thanks a lot for all the help.

    20190622_140044.jpg

    20190622_140100.jpg


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