Electric Fencer testing question.

Discussion in 'General Electronics Chat' started by Eversr007, Aug 4, 2017.

  1. Eversr007

    Thread Starter New Member

    Apr 10, 2016
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    Hi I was going to try and fix this electric fencer for a friend. Not usually the kind of stuff I work on and still learning alot. So these fencers put of around 10KV I think. So just so I'm sure I don't mess u p my meter. The board shouldn't have that much voltage on it until the secondary windings on the transformer correct? Also I looks like everything is AC on the board. Also while I'm here, where would be best place to start at on this thing. It doesn't come on or even try to. Its 12 volt powered. Thanks IMG_3125.JPG IMG_3122.JPG
     
  2. DNA Robotics

    Member

    Jun 13, 2014
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    I would start with those black & red 12v power wires that look corroded. See if 12v is getting to the board. They should be cleaned even if they are working. The next suspect is that switch that is exposed to the elements and looks like it has been replaced already. You may find bad connections under that electrical tape.
     
  3. Aleph(0)

    Member

    Mar 14, 2015
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    @Eversr007 If those 8 pin DIPs are generic numbered u can just check for correct vcc cuz that would prove at least _control_ PSU is working:)!

    So I can't tell for sure from pics but it looks like circuit works by charging cap (which is the large white cylinder) then discharging it into big Xfmr to cause shock pulse on secondary at proper intervals. So watching how and if voltage builds on cap can be diagnostic! So if PSU voltages are ok but cap doesn't charge then Osc is prolly not working which is likely trouble with semiconductor or small onboard xfmr or other problem u can easily trace:)! Now if cap charges but there's no shock pulses then problem can be discharge switching device (prolly SCR) or its control circuit! Otherwise it's prolly output transformer which u can test by just putting ne2 across secondary and momentarily tapping like D Cell battery across primary:)!

    Eversr007 If u post numbers from 8 Pin chips I might be able to give more specific help:cool:

    PS When u get it working make sure to brush off rust on inside surfaces and totally seal enclosure with non corrosive silicone!
     
    Last edited: Aug 5, 2017
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  4. Aleph(0)

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    Mar 14, 2015
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    @Eversr007 I was just thinking that failure of cap to charge can also be caused by shorted discharge switch device (so cap is always electrically across primary) so if circuit draws current but cap isn't charging u can check it out by watching cap voltage with primary disconnected:)
     
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  5. Wendy

    Moderator

    Mar 24, 2008
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    Last edited: Aug 6, 2017
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  6. Eversr007

    Thread Starter New Member

    Apr 10, 2016
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    Thank you all for the help. I have a few questions to help me understand better, but I didn't get a chance to test anything yet and was going to town and was going to pick up the two bigger caps on the board. So I unsoldered them from the board and took them with me. But by the time I got done with family stuff everything was closed so I came home and soldered the old ones back to the board so I could test everything like you all said. I looked up the datasheets on the 8 pin chips to find the pin out. But when I plugged it in to test it, it was working. So I was wondering do you think the capacitors are drying out and the heat made them work short term? What is a SCR? How did you mean to test the transformer with a d battery? So I don't understand why all the components are where they are on any given circuit. So it makes it hard for me to trace things down. I seem to do fine with schematics but those are far and few to come by. I love working on electronics it is very fun and rewarding, but what is the best way to learn how everything works. Is there any books that any of you all would recommend? I would even pay someone to teach me. Or is school the only way to learn it. But with my job,kids, and schedule school will never work. I would like to switch my career to working on electronics for myself. But I have to make enough to survive before I can quit the job. I have a good setup just need more knowledge. I mainly work on cell phones, and started to microsolder on the boards. Thanks for any input you all can give me. I know that was a lot of questions.
     
  7. debe

    Senior Member

    Sep 21, 2010
    1,007
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    The discharge capacitor is probably OK. Along side is most probably the SCR. Measure the voltage across the discharge capacitor while it is still working, it should be around 200-250V DC. What are the Chip numbers?. ELECTRIC FENCE.3.JPG
     
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  8. BR-549

    Distinguished Member

    Sep 22, 2013
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    The IC chip between the electrolytic and the small transformer looks dis-colored. Rectifier perhaps. Check electrolytic.
     
  9. Eversr007

    Thread Starter New Member

    Apr 10, 2016
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    Chip #'s are
    Lm358an
    Ts555cn
     
  10. Aleph(0)

    Member

    Mar 14, 2015
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    Eversr007 fyi the ts555cn is just a cmos 555 timer prolly used as a multivibrator to produce the pulses. The lm358an is a dual op amp which could be used in a regulator loop or like that.

    Eversr007 by disconnecting primary leads from circuit and repeatedly connecting and disconnecting them across a D-Cell battery with a small neon bulb (like ne2) across secondary. Bulb will flash when you connect and disconnect primary to battery. It's normal for it to flash brightest when you disconnect leads from battery cuz field can collapse faster than it can rise.

    Eversr007 since circuit is working even temporarily that proves transformer is good so you don't have to test it at all:)!

    Eversr007 based on circuit working after handling, I say your whole problem is a bad connection or rust flake on board causing short or like that. So plz just thoroughly clean board with compressed gas, wash off any stains with electronics cleaner and check all wires and connections for corrosion and like that! Also check foils for breaks and reflow all solder joints just for good measure! So after doing that just let it run for a few hours and gently heat it with hair dryer or heat gun set on lowest setting (but don't get anything hotter than like 75°C) to make sure it's not temp problem! To be totally sure u can also put it in freezer for a few hours then test it b4 it warms up to make sure it works cold but make sure to protect circuit from condensation when you take it out of freezer!

    So after ur sure it passes those tests plz clean corrosion from inside surfaces and seal enclosure shut with electronics grade silicone sealant or like that and plz make sure to seal around wires and terminals too!

    @Eversr007 You can learn a lot from AAC Ebooks on this site:)!

    Eversr007 IMO school is only absolutely necessary if you want credentials and licenses and like that! If you have the discipline and motivation you can learn anything you want through independent study:) and when ur done you'll have better retention and comprehension than school alone can give cuz emphasis in school is totally on passing exams and not so much on comprehension:rolleyes:!

    Eversr007 Now I have a confession to make! I hold MA degree in one field and PhD in another and I can totally tell you that I'm not an expert on anything:oops:!
     
  11. Eversr007

    Thread Starter New Member

    Apr 10, 2016
    9
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    Thanks for all the reply and information. There is a lot to learn and after applying heat the fencer quit and I sprayed freeze spray on the red capacitor at the bottom right and it started working again. I did that a few times to make sure that was it. Got to order one and clean everything up and I think that will fix it.. Thanks again.
     
  12. dendad

    Member

    Feb 20, 2016
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  13. debe

    Senior Member

    Sep 21, 2010
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    What are the markings on the (red Capacitor) as it may not be? It could be a poly switch which will open circuit if heated & close circuit when cooled. If you posted a picture of the other side of the circuit board we might have some idea as to where in the circuit it is.
     
  14. Eversr007

    Thread Starter New Member

    Apr 10, 2016
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    So this is a variator I guess. Which if I read right it helps with surges. If the fence took a lightning strike or some surge it could weaken it right. When I went to mess with it earlier it didn't work again and just barley sprayed some cold spray on it and immediately started working. So would it be week then??? Plus I can't find a replacement crossing the numbers and don't understand the markings. Thanks for any info image.jpeg image.jpeg
     
  15. debe

    Senior Member

    Sep 21, 2010
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    Its a Varistor (MOV) P24Z50, its to protect from voltage surges Vrms14V, Vdc18V rated to stand 24 for 5min. To test it remove it & test with ohm meter. it should test open circuit. The unit should work with it removed if it is faulty.
     
  16. Aleph(0)

    Member

    Mar 14, 2015
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    @Eversr007 I say problem is not the mov cuz it's in parallel with power supply so if it was shorted it would just blow fuse or burn up and if it was open the fencer would still work (but it wouldn't have surge protection).

    So I say check foils and connections near mov for cracks and like that! Also that doesn't look like multi-layer board but if it is, mov through-holes might double as VIAs so plz make sure to check that too:cool:
     
    Last edited: Aug 14, 2017
  17. dendad

    Member

    Feb 20, 2016
    354
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    I would vote for dry joints. Particularly as it goes and stops. Look for cracks in the solder joints and maybe just resolder everything anyway.
     
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  18. Eversr007

    Thread Starter New Member

    Apr 10, 2016
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    Ok so I reflowed image.jpeg all the joints and mov is fine not sure why it was starting and stopping when spraying it but. Now if you put heat on the long black chip with the number 544115 rfe 1211 it goes off and comes back on with cold spray. So I resoldered it and the components around it. I can't find any data sheets on that chip anywhere
    Also when I have that chip warmed up it seems like the discharge cap is staying charged. Cause I can get it to click on and off by pulling one of the 12 power wires off the battery and tapping the wire on battery posts it clicks and works as it should. But if I leave wire on it won't cycle.
     
  19. debe

    Senior Member

    Sep 21, 2010
    1,007
    200
    Its not actualy a Chip. Its refered to as a Thick Film unit custom made for that particular application. It could be a combination of resistors & transistors deposited on a Ceramic substrate.
     
  20. Ford Prefect

    Active Member

    Jun 14, 2010
    89
    9
    It would be a good idea if you do get this working to take it out of this old box and place it inside a strong plastic waterproof circuit board enclosure box and seal the wires that enter the box with silicon etc.
     
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