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Diode Bridge Rectifier Verification

Discussion in 'Repairing Electronics' started by givknow dge, Apr 4, 2015.

  1. givknow dge

    givknow dge New Member

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    The voltage across the +/- terminals of the PIC above is 5V and that across the opto-coupler is 1.04V.

    I have matched copper traces to components for much of this circuit, with the diagrams penned out. Would you like to have the traces for some specific part of the circiut?

    Thanks
     
  2. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Given your stated problem (no mains sensing), this area:
    upload_2015-4-7_20-5-7.png
    is my guess as the area involved in that process (mostly because of the opto-coupler). Could be totally wrong, of course.

    I'm assuming that the Orange and Gray wires go to the Batteries. Are they being charged? Where does the White wire (at the !) go (come from)? Trying to track down what is powering (or not) the opto-coupler.
     
  3. givknow dge

    givknow dge New Member

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    Right. Makes sense. I will post the traces for these wires
     
  4. dave

    Dave New Member

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  5. givknow dge

    givknow dge New Member

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    The white wire goes to chip LM339N on the Main Board of the UPS given at http://www.electro-tech-online.com/attachments/upload_2015-4-6_0-25-40-jpeg.91812/.
    The opto-coupler shares its ground with that of the bridge above it and its Input voltage comes from a pin on the microcontroller
     
  6. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Please include exactly to what pin# of an IC or uC that a trace (or wire) is attached. By way of standard IC pin 1 referencing protocols, you might find this useful:http://www.evilmadscientist.com/2010/basics-finding-pin-1/ This will also help in identifying the rest of the pin#s on the device(s).
    To what pin# of the LM339 and to what component does the other end of the White wire go on the "Digital Charger" PCB?

    The LM339 is a quad comparator, i.e., 4 independent devices that are used to compare an input voltage against low and high level set-points, such as in a battery charge level checker, or any other voltage level you wish to monitor, such as a mains voltage (once reduced and rectified/filtered to an appropriate DC level).
    OK on the ground. What pin# number of the uC goes to what pin# of the opto-coupler?

    I realize this may strike you as a pain, but this is how trouble shooting, especially by what is essentially email, is performed.
     
  7. givknow dge

    givknow dge New Member

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    No problem at all.

    I'll post the details.


    Thanks
     
  8. givknow dge

    givknow dge New Member

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    Last edited: Apr 11, 2015
  9. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    With the UPS powered up and batteries connected as is normal, please post the voltages at the:
    upload_2015-4-11_16-46-18.png Battery connections (Battery Charger PCB)
    And at:
    upload_2015-4-11_16-53-47.png Pin 9 (+ input to one of the comparators) of the LM339 on the Main PCB.
     
    • Thanks Thanks x 1
  10. givknow dge

    givknow dge New Member

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    Hello cowboybob

    I've run into some problems, but I will post the results in a day.

    Thanks
     
  11. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    OK.
     
  12. givknow dge

    givknow dge New Member

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    The voltage at the terminals labeled "Battery connections" above reads: 12.18V
    The voltage between GND pin and Pin 9 of the LM339 labeled above reads 4.5V

    Thanks
     
  13. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    OK.

    What is the voltage on pin#14 (the output of comparator #3 that has the 4.5VDC signal from the uC on pin#9, above) and where does the signal from pin#14 go? If possible, follow and note the circuit elements until an IC pin is encountered. Please include the chip ID and the pin#.

    With the batteries disconnected from the UPS, does the 12.18VDC (checked as above) change, what is that value, and does the voltage on pin#14 change?
     
  14. givknow dge

    givknow dge New Member

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    Pin#14 reads 4.5V with respect to the GND pin of the same IC. It connects with pin#7 of the IC above namely st hcf4093be. This seems like a Quad 2-input NAND Schmit trigger.
    With the batteries disconnected from the UPS, the 12.18VDC and the reading of pin#14 both go to 0V.


    Thanks
     
  15. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    OK. Got to think about this for a bit.
     
  16. givknow dge

    givknow dge New Member

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  17. givknow dge

    givknow dge New Member

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    Hello
    Let me know if you need any other readings.

    To me it seems that the two black relays on the main circuit board (where the LM339N is located) are not getting their activation voltage. Once they do, the system might start working again. But, it is hard to trace the exact component activating them as:
    -It is difficult to analyze the circuit board in its current position. Moving it to a more convenient position would take the solder off the wires
    -The relays seems to be connected to each other and then to a some resistor/capacitor bank. The latter hides the actual component driving them.


    Thanks
     
  18. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    See if you can trace back from the 2 connections on each relay that are the relays' coil points to:

    1. ground and,
    2. the component (IC, driver transistor or whatever) that is providing the activation signal(s).

    Maybe even see what voltage(s) are present (if any) on the coil terminals. (Be careful to avoid relay contactor connections if the mains are ON). You might need to google the relay type datasheet to get pinouts.

    This may not be the entire circuit involved with the switch-over process (Mains to battery and back) but I'm going on that assumption.
     
    Last edited: Apr 23, 2015
  19. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    IN the example schematic offered by bob

    When AC is on, the Opto IC1 1 will have <=1V with respect to gnd on IC1-3 to the Schmitt NAND which will invert output high to drive the base high @Vbe=0.7 and the collector low @Vce<=1V and activate relay.
    This schematic shows the rectifer bridge connected in the NO ( Normally Open) state and thus activated by the AC. However in this thread, I read a NAND is powered by the battery ( pin14). In any case the DPDT relay must supply power to the bridge to work when the Opto switch is closed ( <1V Vce)
     
    Last edited: Apr 23, 2015
  20. givknow dge

    givknow dge New Member

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    cowboybob and Tony Stewart:
    I am working on your pointers. Will post the results soon.

    General question:
    While I am debugging this circuit with live AC power from the mains, are there any suggestion on ensuring safety and prevention from electric shocks? Is there any guide on such things you guys came across?

    Thanks
     
    Last edited: Apr 25, 2015
  21. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Probably is a guide, but experience, for me, dictates the following:

    Since you're primarily looking for low DC voltages (with some sort of meter) but might encounter Mains AC:

    Making absolutely sure that all parts of your body are not grounded -

    1: Always connect your ground lead first (using an insulated probe) and only to the circuit ground, NEVER the chassis ground
    2. while holding the positive (red) probe ONLY, very carefully touch it to the point (connector, pin, wire, etc.) of interest.
    3. Do not allow the probe to slip from the point of interest
    4. Only when you're confident the probe will not slip, quickly take the reading. Then remove the probe.
     

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