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  1. #21
    Here's a pic of the full board, there looked like a lot of dust on it so I've brushed it all off but it's still reading the same resistance. So are you thinking its the transistor and no the resistor? I had a look at the back of the board and it looked like a short from the pin of the led but it brushed off so maybe it just looked worse

    Sent from my SM-G920F using Tapatalk

  2. #22
    the board is very much what I expected
    basically an all in one UC300 and opto isolated breakout board from what I can see

    looking at your photo
    the 10K resistor is in parallel with
    the 200 ohm resistor that's in series with the FETs gate & drain connections

    your probably seeing the 220 ohms in series with the short circuited FET gate & source

    Click image for larger version. 

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    I expect the 2K resistor is probably limiting the indicator LED current

    whats the 14 pin IC number that you can just see 7 of its pins ?

    Last edited by john swift; 13-08-2019 at 07:20 PM. Reason: add circuit

  3. #23
    This one says HC14
    It's hard to take decent photos!

    Sent from my SM-G920F using Tapatalk
    Last edited by CharlieRam; 13-08-2019 at 07:42 PM.

  4. #24
    that makes sence

    it will be a 74HC14 which is a hex inverter very often used on breakout boards

    Click image for larger version. 

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    I think this shows output 1 is fixed for use as the charge pump output
    Click image for larger version. 

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    Last edited by john swift; 13-08-2019 at 08:00 PM. Reason: add photo of opto isolated output terminals

  5. #25
    Whatever file you posted I can't see it on my phone? So in your opinion do you think it's the transistor with the AA6 that's faulty? And what physically makes that port different? I mean how is that port able to provide enough current to power the solenoid when the others can't? Sorry for all the questions!

    Sent from my SM-G920F using Tapatalk

  6. #26
    yes , I think the AA6 is faulty

    the first file is just a PDF copy of the 74HC14 data sheet

    As the same AA6 transistor is used for all 8 opto-isolated outputs
    the only obvious differance I can see is the charge pump has control of output 1
    and you via mach 3/4 control of the other 7 outputs

    any output should be able to control a relay


    looking back at an earlier post

    Click image for larger version. 

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    I would of thought you should be able to change port 1's charge pump to another pin
    for example to pin 2

    Click image for larger version. 

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    Last edited by john swift; 13-08-2019 at 09:49 PM.

  7. #27
    That's what I thought too but when I tried it didn't work....
    I will have another go tomorrow and report back my findings.
    We have a localish electronics shop so I might give them a ring about replacing the smd.. my hands are way too shaky and my eyes are not much better
    Thanks again for the help

    Sent from my SM-G920F using Tapatalk

  8. #28
    its the sort of thing you need to have some practice before you try to repair a valuable board
    I found scrap PC boards are good to practice on

    the last board I worked on was this XMT-2360 speed control board
    the 14 pin IC , a transistor and a few diodes had been damaged by a short circuit to the speed control potentiometer

    Click image for larger version. 

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    I guess the main issue is finding the new AA6 transistors



    have you checked the relay is OK

    does it work when its connected directly to the 24V DC supply ?
    Last edited by john swift; 13-08-2019 at 10:14 PM. Reason: add PS

  9. #29
    I've been following this thread with some interest. Personally I'd RMA the board for replacement/repair, however, if that's not an option...

    From the photo of the board it's feasible that some of the analogues to the left of the transistors are involved with the charge-pump - it's not clear but if I squint hard enough I can believe it. At this time I'd give-up looking for a "AA6-j" marked device - it isn't present in the top-hits of SMD-marking google hits. but the purpose of the device is clear - a logic-level N-channel MOSFET with a working voltage in excess of 24V with a commutating diode to avoid problems with back-EMF from the relay (this was one area that concerned me originally when considering this device could be a BJT). This would support the traces to OP1 being the only charge-pump output. That, in itself, is somewhat peculiar as I understand that the micro controller on the AXBB generates the charge-pump output to itself - so I'm not entirely sure of the logic behind this decision - the integrity of this safety feature is then at the lowest integrity of the board - likely the program running on the micro controller... but I digress.

    In a bind, I'd look to sweat-off the MOSFET for OP1, and the three resistors for OP2, then haywire the gate signal from the landing pad from OP1 to OP2. This would transfer the charge-pump output to OP2. Or, you could carefully (without overheating) sweat off the MOSFETs for both OP1/2 and swap them - assuming that you don't require the OP2 output. It looks as though any/all of the OP1-8 have the same circuitry/options, with just OP1/2 shifted on the board to avoid the stand-off pillar.

    Or replace the MOSFET with a generic with the same SOT-23 packaging and pinout - there's nothing special about it's function that requires it to be matched to the original. John's mention of the 2n7002 is a suitable device in SMD packaging.

    John's analysis of the failed MOSFET is, I believe, the most likely scenario here. There is a question as to why this failed, but sometimes s**t happens. It would be worth, if possible, diagnosing this more completely before attempting a repair. OP has a meter, it would be sensible to measure the voltage at the "IC" side of the 220R resistor with the output OFF/ON (0V, 5V respectively) and at the transistor side of the 220R resistor (similarly, 0V, 5V respectively). That he mentions the LED turns on/off, however, it a pretty good indicator that this should be working.

    OP asks about a sensible price for a repair shop to perform this - a blind replacement (they won't be able to easily test without a licensed UCCNC installation) would be 5 minutes work and 10 pence of component, but they run a business and have to cover their operating overheads. On a good day - price of a pint, however, if the boss is around I'd expect 30 upwards.

    If the OP was closer I'd offer to help - but it's not really viable (100 miles). But if he wants to play with a hot-air rework setup with stereo microscope then the offer is there.

  10. #30
    Its a pity they had not used a DIL (dual in line ) octal transistor array like the ULN2803
    or a new FET array
    like the Toshiba TB D62381A series DMOS transistor array
    that would enable the user to plug in a replacement

    Click image for larger version. 

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    Click image for larger version. 

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    If the AXBB controller was mine I would remove the AA6 FET
    To prove the 74HC14 and resistors that drive the FET are OK

    then either replace the AA6 FET with a
    Vishay Si2306DS if it has the same footprint

    Click image for larger version. 

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    plan B could be link the Gate & Drain PCB pads

    that would enable the use of a relay and an external relay driver

    for example
    Click image for larger version. 

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    after checking the boards details

    Last edited by john swift; 14-08-2019 at 02:30 PM. Reason: add relay board picture and link !

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