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  1. dorke

    Help! Repairing water damaged PCB from Massage chair.

    Please measure the voltage between pins 14 and 7 of the 74LS00 IC(the one sandwiched between the diodes). What do we get? On the same IC, measure voltages on pins 12,13,11 and pins 10,9,8. Once with the limit up/down optos blocked and once again with them passing light. what do we get?
  2. dorke

    2 transistor circuit input output question.

    @Merlin3189, The Thevnin Theorem is a very important one In circuit theory. Both a concept and a powerful practical lab tool(not in all cases though). It's aim is to simplify circuit analysis. Don't use it ,don't understand it, or whatever if you don't need to ... But,if you do use it, you...
  3. dorke

    Solder terminal to breadboard

    Yes there is a wire that can do the job: For short distance use a cut resistor leg to be plugged into the breadboard. For longer distance solder the needed length wire to a cut resistor leg to be plugged into the breadboard.
  4. dorke

    Need Help finding inductance in a RL circuit

    No, how could they be? It is a different circuit,L1 in the vertical arm. Vout/Vin=(R2+jXL1)/[(R1+R2)+jXL1]=(R2+JXL1)/Z Note: I see now that the notations only,in all the above are wrong!:oops: It should be Vout/Vin like here.(=0.7) But the calculations are correct. So simply replace all...
  5. dorke

    2 transistor circuit input output question.

    Everything is fine except using the term "ignore ". Nothing is ignored! The "Load" is disconnected for the purpose of calculating the Vth and Rth according to Thevinin's Theorem. See this video for a simple explanation (from 3:20 on). and this one too,better I think.
  6. dorke

    2 transistor circuit input output question.

    Hop, You are surprising me here! No,No,No, to think of it as neglecting anything is conceptually wrong. NO assumptions whatsoever are made about the "load" in Thevnin's theorem. You should go through it again,I'm sure you will see that. As for our case here, let me prove that by an example...
  7. dorke

    Help! Repairing water damaged PCB from Massage chair.

    from #264 : "jumpers from Pin 32 to 27/28" It should be 32 to 28/29 ! I'm re-posting the test procedure: remember to plug in all the connectors( CN1,CN2 can be left open when testing the control board without the motor). I added some more test points(see pic below) a total of 10 points. Please...
  8. dorke

    Help! Repairing water damaged PCB from Massage chair.

    Are these 10K ohm resistors ?
  9. dorke

    Help! Repairing water damaged PCB from Massage chair.

    o.k. Let's test what is wrong. Measure the DCV to GND on the UP/DW pins relative to GND,when the motor should be on and off . Like so:
  10. dorke

    Why I prefer electronics to plumbing

    Ha yes, I had Raul Julia on my mind...
  11. dorke

    IR remote for android

    ??? indeed o_O which is it then?
  12. dorke

    Interfacing between Little and Big endian

    I find the Gulliver connection fascinating... Didn't know that , although using the terminology for decades ...:rolleyes: Etymology Danny Cohen introduced use of the terms Little-Endian and Big-Endian for byte ordering in a well-known document in 1980. In this technical and political...
  13. dorke

    2 transistor circuit input output question.

    @john, Here is a trivial Thevenin theorem explanation (not an accurate nor a very good one,just for starters). Notes: 1.Don't understand from the above that the theorem only holds for resistive networks-it holds for any linear network (any Z combinations)! 2.The voltage/current sources are...
  14. dorke

    Why I prefer electronics to plumbing

    @Bob : "Morticia" ? The Addams family , one of the best .... which part do you play? must be the "Thing" , a true Hand(y) man;)
  15. dorke

    2 transistor circuit input output question.

    If you do a Tevenin equivalent of the 5k and 20K bias resistors, you will get a voltage Vbb =8V and a series resistor of 4k. i10K=VE/10k=(VB-0.7)/10K ib=(8-VB)/4k i10k=2*iE=2*(beta+1)*ib=2*(beta+1)*(8-VB)/4k thus 2*(beta+1)*(8-VB)/4k=(VB-0.7)/10K solve for VB and make an assumption on...
  16. dorke

    Help! Repairing water damaged PCB from Massage chair.

    And the value of the "Red-orange" Capacitor ?
  17. dorke

    Help! Repairing water damaged PCB from Massage chair.

    Had some time to look into that "phantom voltage" on the AC motor terminals. The reason you measue it is the fact that there is a snubber circuit(R-C network R=100,C=0.1uF?) between the Triacs A1 an A2 terminals. Since you use a DMM with 10M-ohm input resistance you would measure the line...
  18. dorke

    Led Matrix control Problem WS2812B and T4000

    First thing to check is that all modules get the supply voltage(marked +5V). From the photos it looks like some are not connected. Use a DMM to check the voltage on each module(between it's 5v and GND).
  19. dorke

    Help! Repairing water damaged PCB from Massage chair.

    Hi Jonatan, 1. Your attachment doesn't open. 2. In what way were the Triacs shorted? 3. Please measure the AC motor resistances(between all 3 wires). 4. What were the resistors you replaced, and to what value? 5. I wouldn't worry about that voltage, like Ed said it could be a phantom voltage.
  20. dorke

    DC short circuit calculation formula for copper busbar

    @Harald: "What irks me is how you come to deal with such massive amounts of energy while at the same time lacking some real fundamental knowledge" That is what I meant ,without saying it explicitly. And then the series of "non knowledgeable questions" ... Nothing seems trust worthy here. that...
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