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Timer circuit wont turn off V output

Discussion in 'Troubleshooting and Repair' started by Ernie1979, Nov 21, 2018.

  1. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    Hi all,
    I have a simple 12v pump control that only reduces the output voltage from 13v to 12.4v and hence the pump continues to run. I have replaced the two main Mosfets and IC555. The resistors and caps all test within their specs.
    Any ideas or help appreciated.
    Ernie
    Edit to add further info: This is a OEM control they sell as an option that plugs into the 12v pump. It allows you to turn the pump on or off with a main toggle switch. Its main feature is a potentiometer dial to adjust how long the pump is on or off. eg set at 1 the pump is off for ~ 18secs and on for ~4, at position 8max it is opposite - off for ~4secs then on for ~18 secs. However when off and the LED changes to RED from yellow, it is still outputting 12.45v and the pump keeps running.
     
    Last edited: Nov 21, 2018
    davenn likes this.
  2. davenn

    davenn Moderator

    13,249
    1,746
    Sep 5, 2009
    Hi Ernie,
    welcome to EP :)

    well first off a schematic of your timer and maybe a photo or 2 of it so people can see if there are any problems

    I'm assuming you built this timer?
    Did it originally work and then stop,?
    or did it never work from when you finished the construction ?
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    My bet is that you have the MOSFET around the wrong way. Thus, when it is on, it is on; when it is off, conduction is via the body diode.
     
  4. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    Thanks for the reply.
    No it is a OEM controller for a 12v pump sprayer. There are no visual clues and I have also replaced two of the 4 caps but to no avail. The fact that the voltage drops and the LED circuit switches as it should seems to show the switching side of things is servicable. The Mosfets seemed like the culprit but also no luck. It is like they switch but the gate to shut the voltage off doesn't seem to change much (other than the ~ 0.5v drop). I was expecting the resistors to be at fault but they test ok inspec with their rated colour bands. Ill try to get a decent pic.
     
  5. Bluejets

    Bluejets

    3,444
    698
    Oct 5, 2014
    If you purchased it somewhere, perhaps a link to the unit also?
     
  6. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    Unfortunately they dont show any info relating to the Controller section and definitely no schematics. Just want to charge $1000+ to replace the whole controller. All the manuals and IPB pics relate to the sprayer - nothing on the remote on off controller.
     
  7. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    FYI I edited the original post to add further info.
     
  8. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
     

    Attached Files:

  9. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    If I measure V across the two resistors between the large mosfets, (pic 1) I get the 12.45v then drops to 1.35v. Indicating that this portion switches but voltage at the output is still full battery voltage 13.05v like it is shorted somehow.
     
  10. Bluejets

    Bluejets

    3,444
    698
    Oct 5, 2014
    Your pics need to be square on and high res and in focus if possible so people can make out details.
     
  11. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    The forum continually told me there was an error until I lowered the pic res then they uploaded. Best I could do sorry.
     
  12. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    Quick drawing to hopefully better explain pic 3 of the back of the pcb with the components .
     

    Attached Files:

  13. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    Or held open to let full voltage through.

    Components replaced so far: 2xmosfets , 557 transistor, ic555, 2x35v100 caps.
     
    Last edited by a moderator: Nov 21, 2018
  14. 73's de Edd

    73's de Edd

    2,650
    1,076
    Aug 21, 2015
    Sir Ernie1979 . . . . .

    " they . . .Just want to charge $1000+"

    From what I am seeing of that unit, as being compared to a relative true worth . . . . I hope that those " ECCLESIASTICALLY accursed " . . . ." maternally copulating " . . . . " Sweet Ole Boys " have a 1000 units all tied up in their stock inventory and never sell a single unit, 'til hell freezes over. ! Damn carpetbaggers . . .


    I am just making initial minimum changes a la schematic . . . ..
    I notice that your +12 power supply buss travels across the very top and then drops down to power the 555 and later the 557 LED driver transistor and FINALLY your having it connected into the GATE ? ? ? ? ? of the IRF44. See if it is not being wired as I have changed it to, on the Source . Since Drain and the heat sink tab are being directly connected.

    Looking at the whole assembly.. . . .
    Am I correctly seeing the RED and BLACK stubbed and tinned wires as being the connections to the pump proper, that would terminate at the nearby YELLOW screw Euro connector.
    Meanwhile, the extreme end of the boards 2 pin Euro connector is acccepting the 12VDC power in ?

    Now back to the very slightly revised schema.. . . .
    The 555's pin 3 feeds drive to the Z44 base via the RED DOT line path, along the way it drops off at the VIOLET DOT path with base drive for the 557 LED driver transistor. Also the BLUE dot path feeds to the gate of the STP FET, but with those 4-5 band resistors, 10 ohms seems WAY low, so see if you don't need to add a trailing zero or two.

    Don't know what the STP does, but since I am NOT physically being able to see your "S/W" at top left corner. NOR its wiring GAUGE being used.
    Somehow I want to think that the STP is being a power switch, being turned on, into conduction, by a minimally power / current rated "S/W" by establishing its gate drive. .

    Pee Ess . . . . . I am experiencing an optical " collusion " . . . of seeing a double stacked STP. Surely that is a mirror polished tin plate on that foil heat sink rectangle, that the STP is screwed down to . . . . and casting a mirrored reflection..

    ***** Also tell me what the the Yellow / RED LED action light sequences are, under the different situations .********

    First quick test would be to disconnect from battery and test the ohms reading from D-to S of the 44 and then the STP, with the RED and Black wires still being UN-connected..

    Now I never have seen an IRF 44, with other than its heat sink tab showing, but the STP might be offered in the same exposed heat sink tab exposed, BUT ALSO in a polycarbonate case ( insulated) which only lets you make Drain connection to the center leaded terminal.
    Use an exposed heat sink tab version and you would have to mica insulate the tab, or get an UNWANTED SHORT.

    PSEUDO RE-REFERENCE . . . . . .


    [​IMG]

    https://i.imgur.com/pnGPDyT.jpg

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


    Now, if people EVOLVED from apes, why are there still being apes around ?
     
    Last edited: Nov 21, 2018
    Richard9025 and Ernie1979 like this.
  15. Ernie1979

    Ernie1979

    10
    1
    Nov 21, 2018
    Thanks for the reply de Edd. Info above in your quote typed in BLUE to answer a couple of your questions.
     
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