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Defective PCB/scroll saw

Discussion in 'Troubleshooting and Repair' started by KTW, Oct 2, 2015.

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  1. KTW

    KTW

    273
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    Feb 22, 2015
    Hi guys, I have scroll saw that had variable speed now it only operates on high rpm.
    The switch is ok.
    Is there something specific I should be looking at testing on the board?
    I checked the triac and it's good.
    Thanks.
    Kevin.

    scroll saw.JPG scroll saw2.JPG
     
  2. 73's de Edd

    73's de Edd

    3,085
    1,302
    Aug 21, 2015
    .



    Sir KTW . . . . .


    Use velly-velly Bright light and MAGNIFIER, check VEWY-VEWY cwosely (a la Elmer Fudd ) for dry or floating soldered component connections.

    Looks like there is LIBERAL use of piles of "black pookie" to seal adjustments , hide components and keep their PROPRIETARY secrets of components . . . by the most honnable . . . . Chung Ding Co.

    Looks like you might be able to provide us the ID on the run of the mill Eye Cee within the PINK outline.
    My small right YELLOW boxed component will probably be an Opo-to-trif-o-cal Isolater-er-er, if you can dig thru all the pookie on its top.

    The BLUE boxed items will probably be vertically mounted trimpots, for setting the threshold ranges into the O.I.'s activating diode/emitter.

    Is the item just Southeast of the JELLO star being another vertically mounted trimpot or a TO-220 cased semi ?

    Take metering in hand and check across my two marked connections up the RED DOT path from the two trim pots to the input of the O.I. to see . . . IF . . . there is being a voltage change/transition when you power up and try speed changes.

    Then move to the O.I.'s secondary and read across that portion as AC. It then follows the YELLOW DOT road up to the TRIACS gate. Does that vary, if the primary was varying ?

    Looks like the initiation of drive might actually originate at the corner pin of the 16 pin LARGE YELLOW BOX ENCLOSURE via the PURPLE DOT path.

    Any chance you will able to reveal its top numbering ID , unless it has been wet and dry . . . sanded OFF.

    Plus . . . . . did you lift the gate in the testing of the TRIAC ?


    I stand by now, while you get your hands, fingers and clothes VEWY-VEWY dirty.




    Referencing:



    [​IMG]





    73's de Edd





    .
     
    KJ6EAD likes this.
  3. KTW

    KTW

    273
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    Feb 22, 2015
    Looks like you might be able to provide us the ID on the run of the mill Eye Cee within the PINK outline.
    324E amplifier

    My small right YELLOW boxed component will probably be an Opo-to-trif-o-cal Isolater-er-er, if you can dig thru all the pookie on its top.
    Heavily pookied but I'll see what I can do.
    They pookie these components then discontinue the controller.

    The BLUE boxed items will probably be vertically mounted trimpots, for setting the threshold ranges into the O.I.'s activating diode/emitter.
    These look like transistors.

    item just Southeast of the JELLO star being another vertically mounted trimpot or a TO-220 cased semi ?
    AN7805 voltage regulator.

    This is how I tested the triac


    scroll saw3.JPG

    Thanks for the help.
     
  4. KJ6EAD

    KJ6EAD

    1,114
    159
    Aug 13, 2011
    In accordance with the Chenglish writings of Dr. Edd above, likely point(s) of failure are triac and/or optocoupler.
     
  5. KTW

    KTW

    273
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    Feb 22, 2015
    If that is a 16 pin optocoupler I won't be able to identify it as the stuff they put over it looks and grinds like JB weld.
    Are there several variations of the 16 pin optocoupler?
     
  6. Alec_t

    Alec_t

    2,950
    803
    Jul 7, 2015
    If there's any chance the saw has been dropped or knocked recently, pay particular attention to the solder joints of any of the heavier components. Any high Wattage components are also suspects for bad solder joints.
     
  7. KTW

    KTW

    273
    15
    Feb 22, 2015
    I looked at the soldering with 30X magnification and everything looks good.
     
  8. KTW

    KTW

    273
    15
    Feb 22, 2015
    I powered it up and I have 120volts from the triac and everything along the red and violet dotted lines remain a constant 5.1 volts over to the optocoupler, if that's what it is.
    There is no change in voltage when turning the switch.
     
  9. 73's de Edd

    73's de Edd

    3,085
    1,302
    Aug 21, 2015

    .

    Sir KTW . . . . . . .


    Am I catching some Philippines tagalog dialog . . . . but with it still having its all CRITICAL "open" and "good" "bad," being in Englee . . . . and coming thru.

    One caveat that is relevant to this mode of testing, is that he is using an old school analog meter PLUS his ohms function is being switched just enough upwards
    in that mode, such, that the HIGHER internal battery voltage is being used.
    He finds one unit which has totally crashed from MT1-MT2, another which has a non responding GATE and the third one is being good.
    However, the testing procedure, is being dependent of the polarity of the leads and the bridging of one MT terminal to the GATE to fully turn on the unit,
    from its MT1 to MT2.

    Did your testing FULLY fulfill those parameters ?

    I did not see that you fed back testing info as to your voltage measuring on the input(left) side of the 6 pin optical isolator and its right AC side, that couples in GATE drive.
    The OI's left side should reflect a voltage change, as the speed adjustment is varied from min to max.

    I would test that triac by solder sucking ALL solder from either the solder land AT the triacs gate or BACK at its feed point at the pin at the OI.
    Do a very VERY light touch probing between the gate terminal and its now supposedly "floating land" that t WAS soldered to for CONFIRMED open circuit.
    Then test to see if the motor is not running.

    By the way I APPLAUD your info and answering technique of cutting relevant snippets and answering them just below.
    That way nothing is overlooked ('cept the non forthcoming info on the OI voltages and their variance or no variance with adjustments).

    Your valuable info defines the "pink" IC as being a quad op amp . . .or how you clazee Amellicans say . . . a four section operation amplifier
    that can operate from a single ended supply.

    The left, also YELLOW enclosed item, is NOT an optical isolator, only the right YELLOW enclosed item is the units sole OI.

    Your feed back on the JELLO starred TO-220 cased unit and with a 7805 having a center terminal grounding now makes the PURPLE DOT
    path be a ground buss.

    One grounding path is upwards to the YELLOW IC, it grounds that corner pin, on its path to the right, it branches apart and provides emitter grounding of the

    two OI bi polar driver xstrs (BLUE BOXES).
    BTW can you determine , underneath the pookie, are those being just common sized TO-92 cased plastic xstrs ? Or . .unjustifiably ! . . some
    big ole TO-220 encased units ?
    Their collectors then feed the RED DOT path to the OI's internal emitter diode.
    The 2 xstrs bases copper traces drop straight down to a set of series current limiting/isolation resistors and their drive is being received fron the LM324 at
    the two foil paths entering at its right bottom corner.

    Question:
    On the PINK IC, top right corner, third pin to the left .
    And referencing with my JELLO star, drop straight down the board to the almost bottom and see the one shiny pad and notice just beside it to the right.

    They look blackened, is this just being optical deteris, or did some QC go-go girl mark them with a black Sharpie, after an initial inspection after the production lines
    board flow soldering.
    She then sent them to a rework station for solder touch up, then the BLACK markings was her final inspections mark of approval/and evidence.

    Question probably already answered . . .
    On the "BLACK POOKIE" . . .I was expecting all the way from BLACK silicone rubber blobs, actual blobs of tar or your hardest for removal, being the rock hard Jay Bee Weld Epoxy.

    I am on laptop now, ripping off at a blazing 100 wpm + (so there may be errata). . . . when I get back to home base, I can use a 42 in monitor to overlay and place the boards F&B sides side by side.
    PLUS I will amend the drawing to current circuit finds.
    Recolor the left IC's outline (NOT another OI)
    Can you pass on the average resistor values clustered around and in and outing from that units pins.
    High ohmmic resistor values versus lower ones would differentiate between it being CMOS versus TTL family.
    Also check pins for the highest DC voltage on a terminal.
    I am suspecting this IC to be the "pulse width brains" for the unit, to feed into the 324, which we also already see as fulfilling predriver functions with two of its sections.
    Can you find the speed controller pot and find its center rotor terminal, and see how it indirectly connects (via resistor) into a pin of the mystery IC .
    I am suspecting , pending further facts, for that ? IC unit to be circuit configured as a dual series schmitt triggered function.

    ( My gut feeling . . . .I still tinks youse done gots yerselfs a " buggy/leaky " gate on the Triac)

    Back later with amended drawing . . . but still in need of any of your research findings.

    GO jigsaw GO . . . .GO jigsaw GO ! . . . . no . . . . .pause . . .slow down jigsaw, slow down.



    73's de Edd



    .
     
  10. 73's de Edd

    73's de Edd

    3,085
    1,302
    Aug 21, 2015


    .



    Sir KTW . . . . .

    Somehow ? I totally passed by your 11:35 post with the fact that a CONSTANT 5.1 VDC is on the left(drive) side of the OI, instead of there being a potentially variable pulse width signal.
    So that means the OI is letting a full and continual stream of pulsating + & - nodes from that Full Wave Bridge power rectifier, activate your motor continually to produce full speed..

    On normal adjustable speed operation mode, progressively shorter pulses, determined by the speed control pot, will slow down the motors operational speed.

    To give a clean bill of health to the OI and Triac, solder suck and wick up the middle left terminal of the OI such the the connection to the top left
    transistors collector is opened up.
    Then power up and see if your motor is then not running.
    If so then we have to back track to the LM324 and see at which point that loss of that required variable pulse action is occurring.

    Haven't had time for another mark up photo, but does the speed controls pot come in to the white three pin connector between the corner blue trim pot and
    the LM 324.

    Up at the red power transformer for the units LVPS, is the black device to the top right of it being a mini 4 pin Full Wave Bridge like was made very popular by VARO ?.
    Or is there a possibility mere half wave power is being derived by the power diode passing down to the black main filter capacitor just above the 7805 regulator.

    Also, can you identify the "orange" dee-vice, being just to the left of the top corners 4 resistors ?

    73's de Edd



    .
     
  11. KTW

    KTW

    273
    15
    Feb 22, 2015
    Just on my way out the door for the day but I'll get back at this later tonight and tomorrow.

    Also, can you identify the "orange" dee-vice, being just to the left of the top corners 4 resistors ?
    That would be a 3 pin connector, I can't tell you what it connects to because the saw isn't here but I can find out if you need that information.

    scroll saw4.JPG

    When powered up it spits out 50 vac at the motor pins, the switch has no affect on controlling the speed to the motor.

    This saw belongs to someone else who put an ad out for help with it.
    I waited a week thinking someone with more experience would have contacted him but nobody did.
    This saw belonged to his wife's father and he wants to keep it, he would buy another control but can't find one.
    I'm not charging him anything to fix it unless it requires a new component, he'll pay for the parts.
    Just trying to help him get it fixed and learn something in the process.

     
  12. KTW

    KTW

    273
    15
    Feb 22, 2015
    solder suck and wick up the middle left terminal of the OI such the the connection to the top left
    transistors collector is opened up.

    Opened the middle left pin on the Ol and the motor pin still has voltage, slightly increased after desoldering 15 volts to 65 volts from 50vac.

    The bridge rectifier is KBPC604
     
    Last edited: Oct 3, 2015
  13. KTW

    KTW

    273
    15
    Feb 22, 2015
    I have all but one of the components identified, it looks like a transistor and is marked

    FOR36
    7.E
    Any idea what this one is?
     
  14. KTW

    KTW

    273
    15
    Feb 22, 2015
    transistor.JPG
     
  15. 73's de Edd

    73's de Edd

    3,085
    1,302
    Aug 21, 2015
    .


    Sir KTW . . . . . . .


    You sez. . . . . . . . . Just on my way out the door for the day but I'll get back at this later tonight and tomorrow. . . . . . . . .

    ( Using my best quizzical foreign accent . . . . .where you go ? where you gooooo ? ? ? )

    Answering your very last question first . . . .

    I think that FOR367.E is probably going to be a low power 100 ma scr or possibly a unijunction transistor.
    I ran into the numbering protocol prefix of "FOR" about 30 years ago and it was a Toshiba product origin and is probably obsolete now.


    You sez . . . . . . . . . .I have all but one of the components identified . . . . . . . . . .

    • WHAAAAT ! . . . . Does that mean that you have even got the number for the mystery "epoxy clad" 16 pin IC ?

    Let’s just start up again . . . . and I know that you have only the bare board, less the motor mounted on the unit, and a three pin connector that would be
    going to the speed pot on the unit . . . .also, the saw mounted power switch.
    Lets just utilize a 100 watt incandescent bulb in a table lamp to substitute for your motor . . . . plus . . . that way you will also get a visual display at no extra
    charge . . . you like fries with that ?

    I'm pulling out my redraw of the pcb with its foil side and the component side to its right . . . . . and that was being at the ready months ago.

    I transferred a couple of components across the board, for referencing as a visual overlay, in comparison of the foil side .

    Boards Initial . . . . POINTS OF INTEREST:

    At the very top of the board are the AC power input and the jig saws universal motor.
    The YELLOW line bordering is indicating the AC power line “ HOT “ portion of the board, while the lower portion of the board is AC
    line isolated, by use of the RED power transformer.
    The BLUE rectangle is the drive signal optical isolator which feeds the gate of the POWER control semi mounted on the heat sink.
    Its bottom half contains the driven LED while the top half contains the photo detection portion.
    To the left is a smaller rectangular PINK 4 pin optical isolator.
    Its LED portion is on the top while its photo detection portion is on the bottom.
    The power loop of the motor drive circuitry has a 1/2 ohm power resistor (physically just above) inserted in series such that varying motor load conditions
    can be fed back thru the PINK optical isolator for PWM correction for the motor control circuitry at the bottom portion of the board..

    Info preparation . . . . PRIOR TO INITIAL TROUBLESHOOTING:

    We need preliminary info related to the inter wiring of this PCB to its jig saw mounted components.
    Check the power switch and see if it doesn’t connect into my two marked in BROWN ovals.
    If so, then we merely need a jumper clip between them to simulate a closed switch, and being able to leave the switch on the saw.
    • Get the part numbers from the PINK and BLUE optical isolators.
    • Get the part number of the A.C. POWER SWITCHING semiconductor on the heat sink, so that I can relate to its required gate drive level.
    Find the end to end resistance of the speed control pot on the saw, if it doesn’t pull easily, we can use another like value trim pot at the unit or
    use two half value resistors in series, to simulate a mid-speed adjustment.

    Thassssit . . .for now . . . .

    ADDENDA:
    I had forgotten your second photo of the board . . . so that is giving us a speed control pot and the switch already connected to the board . . .so disregard those prior queries.
    With the only mystery nearby, being the ORANGE connector and its pins and what they connect to on the saw . . . .possibly a tachometer function of motor speed ?

    PAIRED PCB SIDES . . . . . .

    [​IMG]

    73's de Edd
    .
     
    Last edited: Apr 2, 2016
  16. KTW

    KTW

    273
    15
    Feb 22, 2015
    I'm back on the planet.

    Does that mean that you have even got the number for the mystery "epoxy clad" 16 pin IC ?
    Roger that Edd.
    I was looking for a substitute DC motor control a couple of months later and up popped a wood working company with a few of the identical boards for sale without all the epoxy.
    I now have a good board and the original bad board.

    The board.JPG
    The brown ovals are indeed for a potentiometer (variable speed saw)
    The optical isolators are MOC3023 optocoupler Triac-Out and NEC2501 DIP-4 Photocoupler.
    The heatsink is home to a Q6015L5 triac, BTA16 400B on the new board.
    The trim pot is 50K and it's working.
    The voltage is full on causing the motor to run wide open.
    Not sure what the ORANGE connector is, he disconnected it at the saw but I can find out if need be.
    It's in conjunction with the MC14538BCP Dual Precision Retriggerable/Resettable Monostable Multivibrator.
    .

    The board.JPG new board.JPG
     
  17. KTW

    KTW

    273
    15
    Feb 22, 2015
    Here's an interesting note...
    The original board test 108 volts DC regardless of where the pot is turned and the new board measures 106 volts DC regardless of where the pot is turned .
    I'll have to find out where that orange connector goes back to, it may have something to do with the rpm of the motor and I might be working on the wrong end of the problem.
    It appears as if the board runs at full voltage until it can read what the motor is doing.
     
  18. 73's de Edd

    73's de Edd

    3,085
    1,302
    Aug 21, 2015
    .


    Sir KTW . . . . . . .

    You sez . . . . .The brown ovals are indeed for a potentiometer (variable speed saw)
    (The BROWN marked connections are receiving the red wires going to the separate SWITCH that is mounted on the very BACK of the pot )

    CIRCUIT ANALYSIS:

    The orange connector is using one pin for ground, one pin for power and the pin closest to the MC 1453, should be accepting input from a
    Led -Photocell combination with either a slotted metal disc or optically black-clear-black-clear ---> . . . . . plastic disc that is connected to the
    motor shaft and therewith, interrupts the units optical coupling.

    A . . . . . la :

    [​IMG]



    Not sure what the ORANGE connector is, he disconnected it at the saw but I can find out if need be.

    Yep . . . . .looks like that info will be needed . . . .




    73's de Edd


    .
     
  19. KTW

    KTW

    273
    15
    Feb 22, 2015
    Thanks for hanging in there de Edd.
    He's bringing the saw over tomorrow.
    3's
     
  20. KTW

    KTW

    273
    15
    Feb 22, 2015
    Another tidbit.

    conn..JPG
    This three pin connector has 6 volts AC on each pin on the original board and 40 volts AC on each pin on the new board.
    There is a definite voltage drop on the old board.
     
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