troubleshooting digital circuits

[walters]

timing diagrams
1.) triggering problems like what on the logic analysers or O-scope?
2.) sync problems like what on the logic analyser or O-scope?
3.) Timing difference problems like what on the logic analyser or O-scope?


How would i know if i had triggering problems? sync problems? or timing problems in my digital circuits please?

What other digital waveform problems would i be looking for as a digital test tech or troubleshooting digital circuits please?

 

[walters]

What types of digital signals would i be looking at?

1.) control signals?
2.) Data signals?
3.) trigger signals?
4.) write enable signals?
5.) board address signals?
6.) bit combination signals?
7.) parallel and serial address signals?
8.) timing of the signals?
9.) glitch detection signals?

 

[Audioguru]

Since you ask about troubleshooting by looking at signals on a 'scope, then you should learn about the circuits and learn about the 'scope.

 

[walters]

But what signals do you guys know for digital electronic circuits ?

Like what are some basic or general digital signals that are common to know?

 

[Audioguru]

Every digital circuit is different and produces different signals for different inputs.
You must learn how the circuit is supposed to work in order to troubleshoot it with a 'scope.

Maybe you can analyse the working signals from a good circuit and compare them with a defective circuit.

 

[walters]

yes i know

But i just want to know in general what KIND or TYPE of digital signals are ?

Can you please make a LIST of different kinds of digital signals?

Like what would a digital tech be looking for or at on the oscilloscope give some examples please?

 

[Audioguru]

Many consumer products like MP3 players and DVD players are too cheap to fix. Their digital signals are always changing very quickly so you can't use a 'scope to see them.
You can't buy parts for them anyway.

I don't think a tech would bother trying to see the signals in a defective $5.00 clock radio's clock circuit.

 

[walters]

im just trying to understand more about digital electtronics and how someone would troubleshoot them in the 70's they did it more often , how would a digital tech do this back then ??

 

[Audioguru]

In the 70's the logic ICs were DTL and TTL. Simple gates and counters. I had The TTL Cookbook which explained what the ICs did.

 

[walters]

What did the COOKBOOK say about using the oscilloscope when troubleshooting digital electronics?

How do you troubleshoot TTL circuits and DTL circuits?

 

[Audioguru]

I never saw any faulty digital circuits. They all worked fine.
I designed circuits and used my oscilloscope to see if there were any timing problems.

The TTL Cookbook and the Cmos Cookbook don't say how to connect the 'scope. It is obvious how to connect the 'scope and its operating instructions describe how to do it.

 

[walters]

What are some TTL timing problems?

What are some CMOS timing problems?

What ares some DTL timing problems?

 

[dmk]

In my opinion, there is no need to think about DTL, even about TTL anymore. Think only about CMOS (and HC, HCT).
The main parameters of the signals are: rise and fall times, minimum pulse width, propagation delay, setup and hold times.

 

[walters]

What is setup and hold times please?

what kind of problems or errors can you get with rise and fall times, minimum pulse width, propagation delay in digital circuits please?

 

[Mr_Sparkle]

Hi

Digital circuits are mainly main up of gates eg. AND, OR, NOT, NOR, XOR, NAND. One need to know the truth tables. eg. for a two input (A and B) AND gate with one output X ... the truth table is as follows

A B X
0 0 0
0 1 0
1 0 0
1 1 1

When using a scope/logic probe and 1 = high (5V for TTL) and a 0 = low (ground or 0V)

Combination of gates allow one to build a Car Alarm etc.

There are also counters/flip flops/shift registers ... counters (together with a 555 timer or RC connected to the counter) were used for delays, flip flops where used for switching and the PIC RRF and RLF do the job of a shift registers.

Logic Analyzers were using for fast square waves.

Hope this helps

Mr Sparkle

 

[dmk]

Well, it is not easy to explain. Hope this will help, but if you have more questions, refer to book of Wakerly (Digital Design Principles and Practices) or something else, please. You can find many such books in EDAboard.

 

[walters]

Digital Design Principles and Practices) Where at in EDAboard?

You can find many such books in EDAboard where at can u find more books at?

 

[bhanupratap56]

hey when u have scope then set both the signals in same time division and observe then u can know that the singnals are sync or not

 

[walters]

How do you know if the digital logic state is OPEN? not high or low but OPEN? how would i measure that ?

 

[walters]

How would i know if im reading a FLOATING digital signal? how would i tell that its floating ? (not high or not low ) its floating between high and low



Digital troubleshooting:

1.) There is No digital input to the chip
2.) There is No digital output to the chip
3.) Check the Vcc voltages and grounds to the chip
4.) Either the chips output is stuck in a high state or low state or its dead or open
5.) The pull up resistor is open or shorted
6.) What else can be wrong when troubleshooting digital circuits?

Added after 7 minutes:

Digital troubleshooting basics list :

1.) There is No digital signal to the input of the chip
2.) There is No digital signal of the output of the chip
3.) Check the Vcc voltages and grounds to the chip
4.) The output of the chip is not pulsating high or low but is "stuck" in a high state or low state or its a dead line
5.) The pull up resistor is open or shorted
6.) The chips output voltage is reversed polarity when it shouldn't be, its been inverted

What else can be wrong when troubleshooting digital circuits?