Digital Troubleshooting and testing - Page 2 - Electronic Circuits Projects Diagrams Free

Thunderchild · 21st August 2005, 08:21 AM

well to be thorough u need to test every combination (hence that complicated custom equipment i mentioned earlier) but if u know the area of trouble or are able to work it out then it could be simpler. it is not that comliccated u know ? once u have atached the proble to go through all the combinations is childs play just check that u put an 0 and a 1 signal through to make sure that what goes in comes out that just means an on off switch on the input probe or your puting it on and off. or if the chips are socketed and are not that meany (or u have pleanty of cash) just change all the chips. or get replacements say one per type and change them to make sure they work

walters · 21st August 2005, 08:26 AM

So should i start with the Clock pulse first to see if the Timer circuit it sending out a clock pulse?

What are the basic steps from Left to right to start from in digital signal tracking or tracing ?

I have to Check and Test each chips Pin Voltages , Clock Pins, Iinput and out states high or low , what else should i test for or know?

Thunderchild · 21st August 2005, 09:11 AM

start from what apears to be the begining that could be the input of the whole circuit u may want to ensure fist that all the chips r receiving a clock signal if they r supposed to as there could be some clock buffereing circuitry or not gates that may cause a general fault as no clock signal mean no go for anything

walters · 21st August 2005, 09:18 AM

Thanks for helping me out on this

So when troubleshooting or signal tracking digital circuits and components you have to have alot of truth tables ?

I have a logic probe and that takes forever to test ever chip pin to with the truth table to see if its working right

What are some basic digital signs or problems that digital circuit get or have to be more experienced ?

Thunderchild · 21st August 2005, 09:31 AM

the truth table will tell u in ste most convenient way what a circuit does i mean if u were a near geneise u could look at a truth table and know from that what the chip is not/and/nor/en/decoder ecc. there r no common faults as far as i nkow with digital stuff as one chip is worth another i suppose but a hint: what is all this digital circuitry controlling? if it is like transistors that perhaps control relays then check allthat first. i know this is the end of the circuit but the power stuff is more prone to go than the digital stuff and is less time comsuming.
(god what question is that going to lead to i suppose - perhaps u had better tell me what this thing is and does)

walters · 21st August 2005, 09:39 AM

I'm just talking about digital troubleshooting in General to have good
rules to know and learn from but in General to get the concept down so i can use this to apply to any digital circuit that i test

Im just looking how to do testing,checking digital componts and circuits
just the basics but in general rules

Digital Troubleshooting rules:

1.) So first test the Voltages going to the digital components or Chips
2.) Test to see if the Clock pin on the chip is getting a clock pulse
3.) Check the inputs and outputs with a truth table with a logic probe
4.)

What else can i do test or check for?

Thunderchild · 21st August 2005, 09:50 AM

ok that is a very good line of action but if and this will probably often apply as a digital circuit in itself is useless unless it controls something there is something to be controlled like a motor via a relay ecc and say there is just no output then check all the power stuff like 1 the motor thats working ? then go to the relay that controlls it or the transistor. if say a relay is controlling the motor and the relay is being switch by a power transistor then check that often power transistors r not mounted on a sufficient heat sink and so if on for a while burn out if the power section is ok then move on to the difital control. if say the motor (or what ever else) is working but say at the wrong moment (eg the conrol circuitry is not doing its job right) then u may go strait to the digital stuff.
u see designing and making something is one thing - trying to find out why it wont work is: JUST A MUCH BIGGER KETTLE OF A FISH especially if u did not make it and so working out how it works (or was supposed to) is the first best thing and a schematic diagram is the best thing for that. i sometimes if it is not available draw it myself by tracing the pcb but that can get very complicated and i only do it on little stuff (or perhaps i should say would-yea i realy hate fixing a problem making the thing myself is just so much more peace of mind than trying to figure out what another guy got wrong :?: :!: :idea: :arrow: )

ThermalRunaway · 21st August 2005, 11:57 AM

In order to troubleshoot complex electronics equipment such as encoders and decoders you need to get hold of a logic analyser. Logic analysers allow you to monitor multiple data lines simultaneously by taking a "sample" of digital activity. Once a sample has been taken you are able to go back and view the activity that has taken place. Typically you can view this information as binary information, hexadecimal values, octal values or more commonly you can view the information in graphical form. The graphical form is usually a timing diagram which shows which data lines are taking high and low values and when the high-low transistions are occuring in relation to each other.

A logic analyser is invaluable for conducting these kinds of tests and is incredibly useful for troubleshooting your own digital designs. Logic analysers vary in complexity and price, ranging from small devices which can monitor low speed 8-bit systems to high speed equipment which is capable of monitoring in excess of 200 data lines at the high speeds associated with modern microprocessors. The price varies in accordance, from just a couple of hundred pounds for a simple analyser to a few thousand pounds for a good one. Top of the range analysers aimed at industrial and design applications can fetch price tags in excess of £20,000!

For basic applications such as those you are talking about, a simple logic analyser will do and will still make for an invaluable tool. You should take a look at the Pico series of logic analysers which interface to a PC. The PC interface means that you're not paying for a piece of equipment which incorporates all the control knobs, firmware and display screens typical of an "all-in-one" unit. A PC controlled analyser uses the PC's standard peripherals and screen for display and control which alleviates you of these costs. Simple analysers capable of monitoring 16+ data lines of speeds around 20Mhz can be picked up for a couple of hundred pounds, or even cheaper second hand.

Good luck!

Brian

Thunderchild · 21st August 2005, 12:04 PM

thanks brian u gave a better explanation of the logic analyzer than i could ever have given. i was unsure of the name because i studied electronics here in italy and realy wish it had been back in england so i sometimes have a specifics terms lingo difficulty

walters · 21st August 2005, 06:09 PM

Thanks alot for the information

Simple analysers capable of monitoring 16+ data lines to get timing diagrams

Digital Troubleshooting seems to be hard cause you have to monitor alot of clocks and timing diagrams, So i have 16 data lines and im looking at the timing diagrams and inputs and outputs of gates. How do i know if something does not look right beause there is so many data lines , clock lines, inputs and outputs to gate all i am seeing is On and off state at different pulses and waves they all look the same pretty much its very complex to me it just looks like a bunch of diffrent timing clock signals
on a 16 channel oscilloscope how do i troubleshoot from looking at the 16 channel oscilloscope looking at the timing diagrams?

ThermalRunaway · 21st August 2005, 06:23 PM

Well, unless you're actually the designer of the system, it's unlikely that you'll be able to look at a set of timing diagrams and say to yourself, "hang on a minute... the data at this point is not correct". If you're looking at a system someone else has designed, usually all you'll be able to determine is that yes, varying data is present on each data line or no, varying data is not present on a particular data line. Usually, if you have a set of varying data present on a data line it's safe to assume it's not faulty. You don't know that the data is correct, but the fact that data is there (and the pulse train varies) is usually enough to assume all is well. If you were talking about a system which you'd personally designed (which wasn't working properly) you'd be able to use the timing diagrams along with your own design data and IC data sheets to determine whether all the required control lines were being operated properly and with the correct timing. Timing problems can be amoung the most difficult problems to pin down for an engineer or hobbyist.

If a data line appears inactive for a prolonged period of time, it's possible (although not definite) that it's faulty. If it's stuck low for the entire capture period, it could be that this particular data line is short to ground - switch off the equipment and check with a meter. If a data line is stuck high for the entire capture period, it could be that the data line is short to VCC - switch off the equipment and check whether this is the case. On the other hand of course, it could be quite normal for that particular data line to remain in any one state for that particular capture period!

Digital fault finding is probably the hardest kind there is. Sometimes you find a fault (an i/o pin short to ground for example) but even then you're unable to pinpoint the exact IC that's causing the problem. For example, if you have IC1 which outputs information to IC2 via a set of i/o pins, and one of those pins is short to ground, how do you know whether you've got an internal problem within IC1 or IC2? The only certain way to tell is to remove one of the ICs (or at least remove the solder from the offending pin on one of the ICs) and see if the short dissapears. That technique is fine, but what if you're talking about a faulty data line which interacts with 3 or 4 different ICs? Which one is faulty then? And what if all the ICs are SMDs or worse... BGA packages? It really is very difficult

Brian

walters · 21st August 2005, 06:33 PM

Thanks alot this is helping me out alot to talk to someone about this
type of skill to so thanks

you're actually the designer of the system, it's unlikely that you'll be able to look at a set of timing diagrams and say to yourself, "hang on a minute... the data at this point is not correct"

Yes thats what i been doing because i don't know whats right or wrong
its really really hard to tell if the Clock or timing diagrams lines are shifted or has any varies

What would cause a Pulse train or Clock pulse to vary? or shift?

I know there is a Propergation Delay also from going in and out of the digital chips but would the chips make a clock pulse vary or shift ?

Thunderchild · 21st August 2005, 06:33 PM

that last post Brian must have made walter VERY happy hehe u could of spared him perhaps

walters · 21st August 2005, 06:38 PM

yea i really need the help about digital troubleshooting alot its kinda of complex and hard for me to track down by looking at the timing diagrams

ThermalRunaway · 21st August 2005, 06:47 PM

Ok so you're talking about a fault condition which causes a set of data to "vary or shift"? What exactly do you mean by that? Have you got a particular fault which you're unable to track down? If so, what equipment are you working on and what is the fault symptom?

Brian

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21st August 2005, 08:21 AM	(permalink)
Thunderchild	well to be thorough u need to test every combination (hence that complicated custom equipment i mentioned earlier) but if u know the area of trouble or are able to work it out then it could be simpler. it is not that comliccated u know ? once u have atached the proble to go through all the combinations is childs play just check that u put an 0 and a 1 signal through to make sure that what goes in comes out that just means an on off switch on the input probe or your puting it on and off. or if the chips are socketed and are not that meany (or u have pleanty of cash) just change all the chips. or get replacements say one per type and change them to make sure they work __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

21st August 2005, 08:26 AM	(permalink)
walters	So should i start with the Clock pulse first to see if the Timer circuit it sending out a clock pulse? What are the basic steps from Left to right to start from in digital signal tracking or tracing ? I have to Check and Test each chips Pin Voltages , Clock Pins, Iinput and out states high or low , what else should i test for or know?

21st August 2005, 09:11 AM	(permalink)
Thunderchild	start from what apears to be the begining that could be the input of the whole circuit u may want to ensure fist that all the chips r receiving a clock signal if they r supposed to as there could be some clock buffereing circuitry or not gates that may cause a general fault as no clock signal mean no go for anything __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

21st August 2005, 09:18 AM	(permalink)
walters	Thanks for helping me out on this So when troubleshooting or signal tracking digital circuits and components you have to have alot of truth tables ? I have a logic probe and that takes forever to test ever chip pin to with the truth table to see if its working right What are some basic digital signs or problems that digital circuit get or have to be more experienced ?

21st August 2005, 09:31 AM	(permalink)
Thunderchild	the truth table will tell u in ste most convenient way what a circuit does i mean if u were a near geneise u could look at a truth table and know from that what the chip is not/and/nor/en/decoder ecc. there r no common faults as far as i nkow with digital stuff as one chip is worth another i suppose but a hint: what is all this digital circuitry controlling? if it is like transistors that perhaps control relays then check allthat first. i know this is the end of the circuit but the power stuff is more prone to go than the digital stuff and is less time comsuming. (god what question is that going to lead to i suppose - perhaps u had better tell me what this thing is and does) __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

21st August 2005, 09:39 AM	(permalink)
walters	I'm just talking about digital troubleshooting in General to have good rules to know and learn from but in General to get the concept down so i can use this to apply to any digital circuit that i test Im just looking how to do testing,checking digital componts and circuits just the basics but in general rules Digital Troubleshooting rules: 1.) So first test the Voltages going to the digital components or Chips 2.) Test to see if the Clock pin on the chip is getting a clock pulse 3.) Check the inputs and outputs with a truth table with a logic probe 4.) What else can i do test or check for?

21st August 2005, 09:50 AM	(permalink)
Thunderchild	ok that is a very good line of action but if and this will probably often apply as a digital circuit in itself is useless unless it controls something there is something to be controlled like a motor via a relay ecc and say there is just no output then check all the power stuff like 1 the motor thats working ? then go to the relay that controlls it or the transistor. if say a relay is controlling the motor and the relay is being switch by a power transistor then check that often power transistors r not mounted on a sufficient heat sink and so if on for a while burn out if the power section is ok then move on to the difital control. if say the motor (or what ever else) is working but say at the wrong moment (eg the conrol circuitry is not doing its job right) then u may go strait to the digital stuff. u see designing and making something is one thing - trying to find out why it wont work is: JUST A MUCH BIGGER KETTLE OF A FISH especially if u did not make it and so working out how it works (or was supposed to) is the first best thing and a schematic diagram is the best thing for that. i sometimes if it is not available draw it myself by tracing the pcb but that can get very complicated and i only do it on little stuff (or perhaps i should say would-yea i realy hate fixing a problem making the thing myself is just so much more peace of mind than trying to figure out what another guy got wrong :?: :!: :idea: :arrow: ) __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

21st August 2005, 11:57 AM	(permalink)
ThermalRunaway	In order to troubleshoot complex electronics equipment such as encoders and decoders you need to get hold of a logic analyser. Logic analysers allow you to monitor multiple data lines simultaneously by taking a "sample" of digital activity. Once a sample has been taken you are able to go back and view the activity that has taken place. Typically you can view this information as binary information, hexadecimal values, octal values or more commonly you can view the information in graphical form. The graphical form is usually a timing diagram which shows which data lines are taking high and low values and when the high-low transistions are occuring in relation to each other. A logic analyser is invaluable for conducting these kinds of tests and is incredibly useful for troubleshooting your own digital designs. Logic analysers vary in complexity and price, ranging from small devices which can monitor low speed 8-bit systems to high speed equipment which is capable of monitoring in excess of 200 data lines at the high speeds associated with modern microprocessors. The price varies in accordance, from just a couple of hundred pounds for a simple analyser to a few thousand pounds for a good one. Top of the range analysers aimed at industrial and design applications can fetch price tags in excess of £20,000! For basic applications such as those you are talking about, a simple logic analyser will do and will still make for an invaluable tool. You should take a look at the Pico series of logic analysers which interface to a PC. The PC interface means that you're not paying for a piece of equipment which incorporates all the control knobs, firmware and display screens typical of an "all-in-one" unit. A PC controlled analyser uses the PC's standard peripherals and screen for display and control which alleviates you of these costs. Simple analysers capable of monitoring 16+ data lines of speeds around 20Mhz can be picked up for a couple of hundred pounds, or even cheaper second hand. Good luck! Brian

21st August 2005, 12:04 PM	(permalink)
Thunderchild	thanks brian u gave a better explanation of the logic analyzer than i could ever have given. i was unsure of the name because i studied electronics here in italy and realy wish it had been back in england so i sometimes have a specifics terms lingo difficulty __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

21st August 2005, 06:09 PM	(permalink)
walters	Thanks alot for the information Simple analysers capable of monitoring 16+ data lines to get timing diagrams Digital Troubleshooting seems to be hard cause you have to monitor alot of clocks and timing diagrams, So i have 16 data lines and im looking at the timing diagrams and inputs and outputs of gates. How do i know if something does not look right beause there is so many data lines , clock lines, inputs and outputs to gate all i am seeing is On and off state at different pulses and waves they all look the same pretty much its very complex to me it just looks like a bunch of diffrent timing clock signals on a 16 channel oscilloscope how do i troubleshoot from looking at the 16 channel oscilloscope looking at the timing diagrams?

21st August 2005, 06:23 PM	(permalink)
ThermalRunaway	Well, unless you're actually the designer of the system, it's unlikely that you'll be able to look at a set of timing diagrams and say to yourself, "hang on a minute... the data at this point is not correct". If you're looking at a system someone else has designed, usually all you'll be able to determine is that yes, varying data is present on each data line or no, varying data is not present on a particular data line. Usually, if you have a set of varying data present on a data line it's safe to assume it's not faulty. You don't know that the data is correct, but the fact that data is there (and the pulse train varies) is usually enough to assume all is well. If you were talking about a system which you'd personally designed (which wasn't working properly) you'd be able to use the timing diagrams along with your own design data and IC data sheets to determine whether all the required control lines were being operated properly and with the correct timing. Timing problems can be amoung the most difficult problems to pin down for an engineer or hobbyist. If a data line appears inactive for a prolonged period of time, it's possible (although not definite) that it's faulty. If it's stuck low for the entire capture period, it could be that this particular data line is short to ground - switch off the equipment and check with a meter. If a data line is stuck high for the entire capture period, it could be that the data line is short to VCC - switch off the equipment and check whether this is the case. On the other hand of course, it could be quite normal for that particular data line to remain in any one state for that particular capture period! Digital fault finding is probably the hardest kind there is. Sometimes you find a fault (an i/o pin short to ground for example) but even then you're unable to pinpoint the exact IC that's causing the problem. For example, if you have IC1 which outputs information to IC2 via a set of i/o pins, and one of those pins is short to ground, how do you know whether you've got an internal problem within IC1 or IC2? The only certain way to tell is to remove one of the ICs (or at least remove the solder from the offending pin on one of the ICs) and see if the short dissapears. That technique is fine, but what if you're talking about a faulty data line which interacts with 3 or 4 different ICs? Which one is faulty then? And what if all the ICs are SMDs or worse... BGA packages? It really is very difficult Brian

21st August 2005, 06:33 PM	(permalink)
walters	Thanks alot this is helping me out alot to talk to someone about this type of skill to so thanks you're actually the designer of the system, it's unlikely that you'll be able to look at a set of timing diagrams and say to yourself, "hang on a minute... the data at this point is not correct" Yes thats what i been doing because i don't know whats right or wrong its really really hard to tell if the Clock or timing diagrams lines are shifted or has any varies What would cause a Pulse train or Clock pulse to vary? or shift? I know there is a Propergation Delay also from going in and out of the digital chips but would the chips make a clock pulse vary or shift ?

21st August 2005, 06:38 PM	(permalink)
walters	yea i really need the help about digital troubleshooting alot its kinda of complex and hard for me to track down by looking at the timing diagrams

21st August 2005, 06:47 PM	(permalink)
ThermalRunaway	Ok so you're talking about a fault condition which causes a set of data to "vary or shift"? What exactly do you mean by that? Have you got a particular fault which you're unable to track down? If so, what equipment are you working on and what is the fault symptom? Brian