# Current Circuits, DVM meter will short out when measuring on current circuits

Discussion in 'General Electronics Chat' started by Billy Mayo, Dec 17, 2013.

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1. ### audioguruWell-Known MemberMost Helpful Member

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Both inputs of U7 are connected together making it a simple Cmos inverter, not a NAND gate.
Don't guess wrongly about the 4043, look it up.

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3. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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I think CR11 should act as a -0.6 V clamp which I don't think it is doing.

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5. ### audioguruWell-Known MemberMost Helpful Member

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Their truth tables are so simple that I am surprised that you do not know. Maybe you do not know English well? Or means or. AND means and.

To make a NOR gate. U7A has both inputs connected together making an inverter, not a NAND gate.

You are missing an education in the basics of electronics.
When the anode of either or both diodes is/are positive then it/they conduct and raise the input voltage of U7A.
When the anode of a diode is low then it does not conduct and does nothing.
When both anodes of the diodes are low then R110 pulls down the input of U7A to be low.

The anode is the input. If the anode is high then it conducts and pulls its cathode high. If the anode is low then the cathode and the input of U7A can be made low by R110 or made high by the other diode, then this diode is reverse-biased and does not conduct so it does nothing. It has two diodes making an OR gate. If either (one OR the other) OR both inputs are high then the output is high.
An AND gate has its output high only when one input AND the other input are both high. Simple English.

Logic does not "pass through" a diode. Look at the diode to see if it conducts or if it does not conduct.

6. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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Way back when there was a logic family called DTL: See: http://en.wikipedia.org/wiki/Diodeâ€“transistor_logic Before that, there was a logic family called RTL or Resistor Transistor Logic.

The Diode trick appears every once and while and is used as a Wired OR even without a transistor. I used two diodes in the car, to make a buzzer work when only the driver's door was open and the headlights were on.

7. ### audioguruWell-Known MemberMost Helpful Member

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I am leaving this silly thread because I am tired of answering millions of questions about simple basic electronics.

8. ### Billy MayoMember

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well whats the problem with the board if its so simple? i got my soldering iron fired up ready to go tell me what to change to fix this problem? and what is that buss called? its very basic and simple ?

9. ### Billy MayoMember

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the designer had an NAND gate, then he uses it as in inverter , and then uses diodes and a resistor as a nor gate , there is a reason why the designer did this

why didn't the designer use a nor gate ic chip? why didn't the designer use a inverter ic chip instead of using an NAND gate as an inverter

10. ### 4pyrosWell-Known MemberMost Helpful Member

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OMG these boards go in planes!!!!!!

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11. ### Little GhostmanWell-Known MemberMost Helpful Member

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Are you making a joke? or are you really serious?
I dont mean to rude at all but, I can see no way that erm, well i just dont see how these are for planes?? I always thought anything to do with flying was strictly controlled? How do you get a job fixing plane stuff with no qualification's? How does a company get a contract to fix plane bit's? with poorly trained staff and sherbert equipment?
None of this makes any logical sense to me. As for AND, OR,NAND,NOR gates etc and diodes, every book I have, has got these in the first chapter or two, so how can you work with them and not (NOT) know? They even give a small clue in there names!!!
AND ____ means both or one AND the other one = HIGH
OR _____ means ONE OR the other ONE means output = HIGH
See there is a clue, anything with a N in front basically means its back to front.
But planes, NO i dont believe that for a minuet. Too many would be falling out the sky, Maybe helicopters? we had one hit a pub in Scotland the other week, so helicopters would make sense

12. ### Billy MayoMember

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When you clear the RESET on latches , the latches shouldn't keep a voltage it should be at zero volts

1.) When I switch on the Enable switch to the Latch CD4043 , It will output a +14 volt , why is that , it should be zero volts right?

2.) There is a CD4017 Decade counter before the Latch CD4043, The CD4017 Decade counter takes 3 seconds to output a pulse to pulse the SET input pin on the Latch CD4043

Why am I getting an output on the Latch CD4043 in milliseconds Way before the CD4017 Decade counter?

When I switch on the enable switch back and forth 10 times , I will get 10 output pulses from the Latch CD4043, how can that be? when the CD4017 Decade counter has to take 3 seconds to output a pulse to trigger and pulse the LATCH set input pin?

Is this Latch CD4043 defective?

What's the Difference between a Flip Flop VS a Latch?

The CD4017 is a Decade counter
The Clock input pin has a 1 hz = 1 second

So it takes 3 clock pulses to output on Pin#7 of the CD4017

13. ### jpanhaltWell-Known MemberMost Helpful Member

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If you look closely at some of the labels, one interpretation could be that the controls mentioned, e.g., flap, pitch gyro, roll, and slat, are aircraft controls. In fact, it may be the autopilot.

I hope it is not for an airplane "made in China to Boeing specifications."

John

14. ### Little GhostmanWell-Known MemberMost Helpful Member

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So what your saying is, we just have to look for the planes that are lost?
Maybe it's one of those fakes China make, Didnt know you could buy jets on ebay
Enough joking, I honestly find it hard to work all this out, I wont post what confuses me, I dont want to be rude or upset people. This time i will keep my mouth shut, but i wont be moving, and you will never get me on a plane again!
So many good people needing jobs.

15. ### 4pyrosWell-Known MemberMost Helpful Member

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Yes I am afraid to contribute to Billys threads anymore.
If he really is trying to repair aircraft boards by forcing outputs or replacing every chip than I may never fly again ether!

16. ### ericgibbsWell-Known MemberMost Helpful Member

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Hi guys,
E

17. ### JimBSuper ModeratorMost Helpful Member

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But what is the topic?

The title of the thread is:
Current Circuits, DVM meter will short out when measuring on current circuits

That is all over the place before we start.

As the board under "repair" appear to be used in a aircraft, that should raise concerns for any responsible engineer/technician.

JimB

18. ### ericgibbsWell-Known MemberMost Helpful Member

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hi Jim,
I agree the topic is somewhat ambiguous , but posts like #213 and #214 have no technical content whatsoever regarding the OPs query.

With regard to the 'safety' aspects of the OP's work, I would say it his employers who are responsible for ensuring safety standards for their work.
Eric

19. ### Little GhostmanWell-Known MemberMost Helpful Member

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GM11
" So a plane goes down, and you sleep easy, because it was there duty to ensure safety and not your responsibility to raise concerns? Sorry Eric i am truly shocked, that you hold such views. IF these are for planes, then how responsible is it to continue to answer these posts with technical help? "
posted by Ghostman11 not LG

20. ### ericgibbsWell-Known MemberMost Helpful Member

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I did NOT say it was NOT my responsibility, read my post.!
Safety of any commercial product is the sole responsibility of the company who provides or monitors the product.

How is the nonsense in post #213 going to improve the safety aspect of the OP's services.??

E

21. ### JimBSuper ModeratorMost Helpful Member

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Eric, you are quite correct.
Would the OPs employer be happy to read these discussions here on ETO?
I wonder.

What I am about to say could form the basis of a separate thread on the ethics of discussing your employers business on an open forum.

We do not know which country the OP is from or which company he works for.
My own personal ethic is that I do not discuss details of my former employers business or my clients business since I have been self employed.
Obviously over the years I have related various experiences and happenings in order to illustrate points being discussed here on ETO.
Having said that, unlike the OP, I do not drag out a tail of woe and incompetance which drifts from one OMG WTF to the next one.

Many people here have tried to give good advice and direction on various aspects of faultfinding in electronic systems, but it all seems to fall on deaf ears.

Sadly there is nothing positive that I can add to this or any of the other related threads.

JimB