so you're talking about a fault condition which causes a set of data to "vary or shift"?

Yes but just in general so i can apply it
when the clock pulse is offset and it throwing off the timing of the digital chips to act faulty or not give the result or function right

How to track down a faulty data or clock line?

Have you got a particular fault which you're unable to track down?

Yes like a Digital chip but just in general how would a tech. track this
faulty digital chip ?

What are some General digital fault symptoms?

 

Well you can normally tell whether a clock is faulty by sticking an oscilloscope probe on it, assuming you have one and assuming it has a bandwidth high enough to display the clock signal. If the clock speed were to drift off slightly, it could give some quite weird fault symptoms. In general, the timing should not be effected by a clock signal which had drifted from it's specified frequency. If the clock was slower than that which is specified, it would mean that the CPU (or whatever type of IC) would run slower than originally intended. Provided this drift was only slight, the control timing should remain unaffected. If the drift was such that the CPU could not operate fast enough to act on the control data then yes, you would end up with screwed up timing and without doubt, the system would crash. If the clock were to run faster than the specified rating, you could end up with a similar effect except that overclocking a CPU is dangerous and could end up actually destroying the IC itself.

Quite often a faulty clock signal will be caused by the oscillator or crystal oscillator itself. I've often had situations where the clock signal becomes erratic once the crystal oscillator has warmed up. In order to diagnose this kind of problem you can spray the oscillator with freezer spray to see if your fault clears. If it does, it's a sure bet that the crystal oscillator is causing the fault. crystal oscillators are also very prone to damage from shock.

Brian

 

THanks ThermalRunaway

So to test a Faulty Clock is put the oscilloscope probe on the output of the
555 timer or clock generator and watches its Frequency and to see if its
varys or shifts in time?

How do i test or check faulty logic Gates : do i check every pin with a truth table ?

How do i test counters up/down or 4-Bit Binary Counter?

Do i test the Reset pins? to see if its a high or low state?

 

I just put my oscilloscope probes on the BUS wires or lines to see it i get
any High or low states or clock signals

 

How does a Tech. know if the "time intervals" are right and not faulty on the bus lines or going to the digital components?

How does a tech. know if the "clock cycles" are right and not faulty on the bus lines or going to the digital components?

 

I did this for many years.

For the most part you read the fault discription and change D7 because the last 500 boards you repaired with that fault it was D7. Test it and tag it, on to the next. 80% of the time this is what you will be doing.

Ok for starters you have to understand the circuit, you need to know how it works otherwise you are wasting your time. If you know what the device is supposed to be doing you can rule out 95% of "what could be wrong" just by looking at what it is doing or not doing.

Oscilloscope would be my test instument of choice.

Step (1) read the fault discription
Step (2) is it a production fault? Knowing if it ever worked is worthwile as you could have incorrect component, solder shorts that would be very unlikely in a returned item. Production faults can be the hardest to fix at times or the easiest. Missing chip or shorted track under a chip etc.
Step (3) Check your power supply
Step (4) This is where you need to know the product and the fault. You just start ruling out possibilites and eliminating them one by one.

You have traced out your circuit and suspect C10. Change it, you most likley cannot test it in circuit anyhow. Does it work yes/no. If no go on to the next most likley component, rinse and repeat.

 

read the fault discription

Where do i get that from the Date sheet of the digital component?

 

listen mate what i do is the half-split method. it is the best method you can use. you can use any test instrument you want cos all your looking for is a voltage or not, a 1 or a 0.

1 Turn the equiptment on

2 look at what the board is telling you. if it has LED's that should be lit, are they? if it should be doing somthing is it?

3 from the symptoms, deduce what elements of the system are working and what COULD not be working. write it down.

4 go to a area that is possibly at fault and look for a correct output. is there a correct output? if there is, try the other possibilities.

5 If you find a incorrect output then half-split the board between what you know is servicable and your incorrect output. Is the logic there correct? if it is then go betwwen there and the faulty output, if its not go between where you are and your servicable input.

6 you will eventually get down to one componant and thats when you test all its inputs and outputs to see if they are correct.

hope this helps.

 

The reason someone sent you something to repair means that the person that sent it to you thinks it is broken. These people for the most part will write down what is wrong with the device i.e. a fault discription.

For examples:
DVD player - remote not working
Good place to start after reading this is checking the remotes batteries. Getting another remote and testing that on the DVD and so on. There may be not need to open the DVD player up at all.

Mobile phone - screen gone funny
maybe bad solder join on LCD screen? faulty LCD Screen. Check the inputs to the LCD.

PDA - not working
not too helpful here, sometimes they just say "it's broken" so you have to start testing it yourself. Often you will not find any fault at all.