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CTEK MXS 3.8 repair

Discussion in 'Power Electronics' started by bushtech, Aug 21, 2018.

  1. bushtech

    bushtech

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    Sep 13, 2016
  2. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir bushtech . . . . .

    A query . . . back to the controller IC . . . . . . . is that 8 pin unit missing its pin 7 ?

    Confirming, with that forthcoming info . . . . . see if that likely NCP1271 controllers output pin # 5 either goes to the shared bases of a tandem pair set of complementary transistor drivers, being arranged as a rail to rail totem pole driver, of which , they then have their shared central collector-emitter junction feeding into the gate of the pooooopped power FET.

    Its popping should have introduced a high voltage into those driver transistors, of which, you have already explored the PNP counterpart, but now need to seek out the nearby NPN companion, to ascertain its condition.

    I will now be looking at the Mantech site, to see if they have any Infineon N channel 600V rated, logic level drive Power FETS that could sub in for what you currently have.

    73's de Edd
    ......................
    Education is . . . Learning what you didn't even know that you didn't know.

     
    Last edited: Nov 2, 2018
    bushtech likes this.
  3. bushtech

    bushtech

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    Wowee! St Edd. Right on the money as always.

    Pin 7 of the NCP1271 is indeed missing.

    There is a complimentary set of transistors, 2fe and a6w. Pin 5 is connected to the connected bases of these two.

    The gate of the mosfet is connected to the emitter of the 2FE. From emitter of the 2FE the connection runs through a 22 resistor to the common of the a6w.

    Thank you thank you
     
  4. bushtech

    bushtech

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    Sep 13, 2016
    Here's a photo of that area:

    totem.jpg
     
  5. bushtech

    bushtech

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    Sep 13, 2016
    When I search for that A6W transistor I get to a MMBTA05 Gen Purpose NPN transistor. Is this it?
     
  6. bushtech

    bushtech

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    Sep 13, 2016
    @73's de Edd

    St. Edd, hopefully this helps. Attached is a LTSpice file showing the circuit from power in through rectifiers and mosfet and to the 2 tandem transistors and their connection to NCP1271.

    Please excuse any errors as I battle with LTSpice and it's tricky plotting an unnumbered pcb. Diodes could be pointing the wrong way etc. Please ignore the two unattached inductors on the right. I am trying draw the transformer with it's 4 primaries and 5 secondaries.
     

    Attached Files:

  7. bushtech

    bushtech

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    Sep 13, 2016
    Bit of an oddball question: I pulled the 04N60C3 mosfet and then powered up to check some voltages. Instantly blew fuse on power up. On checking I notice a dead short between the drain and source holes on pcb. Is this how it's meant to be or have I got a short somewhere else?
     
  8. bushtech

    bushtech

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    Sep 13, 2016
    Sorted this particular problem. 3 of the 4 rectifier diodes blown.
     
  9. bushtech

    bushtech

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    Sep 13, 2016
    I want to replace the two tandem transistors marked 2FE and A6W. On closer inspection of my photo in post #44 the 2FE could actually be a 2F.
    Searching for this transistor brought up this: https://www.google.com/url?sa=t&rct...MBT2907A.pdf&usg=AOvVaw0h21C5BkliR-WwIFQC51Pn
    This could be correct but could somebody please confirm.

    The A6W is a bit more tricky. Downloaded all the smd code lists in our resources section and some others. Various components come up but I have no way of saying which one is correct. Can somebody please help me to find the correct replacement transistor.
     
  10. 73's de Edd

    73's de Edd

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    818
    Aug 21, 2015
    Sir bushtech . . . . .

    If me, I would be using leaded transistors and a 2N2907 would be the PNP amd a 2N2222 for the NPN since they are siamese twins on their specs.

    I would be shortening the stock leads just enough so that you would be able to swing their CBE leads around into PROPER pin alignment ( TRIPLE CHECK ! ) to their perspective pads, yet with them still being long enough to be able to result in a NEAT installation.
    Be sure to pre tin the leads, so that they will then just rapidly melt into place on the solder reflow of their installation.

    I was unable to get back in time for the full wave bridge diode conundrum, with its 4 discrete surface mounts (1N4007 equivalents) and was certainly just expecting 1 or more dead shorted diodes, as your problem.

    The thing about this design, in its using an appropriately selected value of series capacitor to reduce line voltage on down to create a low voltage supply, is that it folds up on its power output, if being overloaded from the norm.
    ERGO . . . with your controller IC receiving some degree of isolation by the totem driver transistors and the power supply folding back, we might now take a feeling for the pulsebeat of the controller IC .

    Do you have a small pocket shirt size AM radio receiver ?

    73's de Edd
    ...................
    People can be divided into three groups:

    Those who make things happen, those who watch things happen, and those who wonder WHAT the hell just happened ? ? ?




     
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  11. bushtech

    bushtech

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    Sep 13, 2016
    Thanks a mill St Edd

    Pocket sized? No, not for many years;)

    But I have this:
    Radio.jpg

    Hope this can work.
     
  12. bushtech

    bushtech

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    Sep 13, 2016
    St Edd, I am quite happy soldering smd components on. Is there a specific reason for going with leaded components? If something like higher reliability, etc then I will go with leaded components but if not I would prefer to go with smd components
     
  13. 73's de Edd

    73's de Edd

    2,442
    818
    Aug 21, 2015
    Sir bushtech . . . . .

    OK then . . . . I was just thinking back to one of your pics of one unit of a set of 2 wireless switch boards of yours, a couple of years back . . . . . maybe muuuuuuuch practice / experience and a small tipped soldering iron, has now imparted a threshold of quasi perfection.

    The 2907 and 2222 are available as surface mount parts.

    73's de Edd
    ...................


    I prefer going to Dollar General, as you do not have to dress up for Dollar General like you do if you go to Wal Mart.

     
    Last edited: Nov 13, 2018
    Tha fios agaibh and bushtech like this.
  14. bushtech

    bushtech

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    Sep 13, 2016
    Me and my soldering iron have walked a long road since then.

    How about the AM radio?
     
  15. bushtech

    bushtech

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    Sep 13, 2016
    St Edd
    I found another forum post where you describe the usage of the AM Radio and tried it. Couldn't hear anything above the crackling of the AM radio no matter how I rotated it.

    I had previously measured voltages on the NCP1271
    FB pin 2 = 3.6V
    Vcc pin 6 = 9V
    HV pin8 = 328V
    No reading on the other pins (which I suppose is logical)

    I decided to recheck those readings and while I was reading pin 8 a 1.5kΩ resistor decided to fry itself and depart for the happy hunting ground. No idea why this happened, pin 8 is conveniently freestanding with no pin 7, so short caused by probe unlikely. Ground used for measurement was neg of big cap.

    It's the 152 resistor shown by the left most arrow.


    Bottom 2.jpg
    I must also add that the NCP 1271 was running pretty hot when switched on through dim bulb tester
     
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