power-off troubleshooting tips

[tracker]

After reading the posts, i found some new users searching for power-off troubleshooting tips and most of the info on the site is for advanced huntron users. Hope this helps someone out there.

This is what i do when i have a faulty board.

I start by studying the board , looking for symmetry , repeatability in the circuits.
Next, i  look at all the ic numbers on the pcb and find their data sheets, especially their pinouts.
Based on that i try to figure out how the board works or at least get an idea of what it is doing.
I prefer not turning on the power when troubleshooting .

I only  power on to  check if it works after i replace components .
When power is applied ,i find things get very complicated.
More than 70% of the time ,i manage to find faults in both digital and analog circuits just using trackers to spot differences.
If all else fails ,then i power on to do some functional testing ,test with multimeters ,scopes and other instruments; looking at board calibration ,function etc .

Nowadays I start testing all electrolytic caps first with an esr meter. The rest i look at with a tracker. High stress high  heat  components are tested first ie those on heat sinks,then diodes,transistors in that order, all the time carefully looking for burn marks or any telltale signs of physical damage.Any socketed ics eg memory,i take out and check their firmware on a programmer.
I always try to get exactly the same boards or  modular boards to compare against. I am from the time where data storage did not exist,so i got used to realtime comparisons....it has worked well for me so far. I don't spend a lot of time learning signatures into a database for comparisons.Nowadays storage is the way to go ! Storage has advantages ,you CAN store data sheets,pinouts ,photos ,videos ,testing notes (like reminders) , and other symptoms observed and link them to signatures,  so you don't have to search for them every time.Also when people leave the company ,their work done  ,info gathered and other data does not leave  with them.

When using huntrons , i find 3 ranges  is sufficient... too many ranges only leads  to confusion without increasing  my chances of "seeing"  faults.

I think of trackers as "xray machines" for electronic circuits. A doctor would ask for  an xray of his patient  if he needs more info . Symptoms are good but Xrays  are better for accurate diagnosis. In the end its all about what we can see and analyse to help increase our  observation and diagnostic skills ....Signatures "talk" to me because i am confident that when electronic circuits fail,they fail at the input -output pins. They go open or  low R when they  have been stressed ,either by the circuit design or by something external .

I keep all the faulty components i have found over the years... building up my trophy collection  
When i have time i plan to post pics of my fail ic collection for the benefit of everyone.The idea is once you see what failures look like on trackers,it may help you spot them when you are trying to find them.... its a good study on how components fail.  

To sum up ,when troubleshooting ,I like to use something simple to  see the fault. Huntrons allow me to see more with their current limited AC, compared to multimeters with only DC.They also will  not damage  the board i am trying to fix. I  do not have to worry about polarity while probing, which saves me time.

Using huntrons CAN be addictive, once you use it ,you CAN'T live without it.  

Hope this helps , happy probing!

[admin]

Great input, Tracker!

I follow and teach many of these same troubleshooting and learning steps myself (like saving bad components).

One question, do you find an ECR meter better on the electrolytics?

Thanks.

Curtis

[tracker]

Hi Curtis,

At first i was skeptical, then i bought an ESR 70 from peak uk, tried it on a few switch mode  power adaptors for notebooks  and now i am a convert...Here is why

In my opinion ,ESR meter readings are one case where a reading is better than a graphic display .Using them in-circuit or out circuit,you get a faster conclusion for electrolytic caps whether they are good or bad.

1 You  don't need to compare against another good device.Sometimes you can't get a good device to compare against . Then ,you may have to start desoldering   the cap and then take a measurement.Using the esr meter you don't have to do that. You just clip on the croc clips across the cap and it will automatically start the measurement . The unit will auto detect when you move on to the next cap and start to test again. Within a very short time ,you would have gone through all the caps on the board.
2 It will  detect if there is a charge on the cap and start to discharge it before making a test ..After the test is complete  ,It even powers itself off to save battery power .
3 Only two hands needed !!!  no" third hand" ( or foot switch ) to change ranges 
4 Lead resistance can be zeroed out , so can go low ohms, down to 0.05 ohms
There is something about sending 100khz into a cap and getting a precise value of ESR and Capacitance side by side ,which is reassuring to me.

Very seldom does stray resistance from another circuit connection interfere with the ESR value measured from a  cap .It can do out of circuit measurements but Of course it is no match against a sencore LC 102 ,which tests caps out of circuit at their working voltage. 

Still finding new uses for it...Get one to try  ,will be interested to see what you think

Maybe huntron can  put esr  into  2800 on next firmware upgrade.

[admin]

Thanks

[jvthorsley]

Made my Altas ESR 60 easier to use by soldering some old EMI gramophone needles on to the Croc Clips as shown on photograph, and easily replaced when they get blunt from stock I have. Good for working on PCB's coated with lacquer.
As stated elsewhere on this forum a good ESR meter is essential with any impedance signature analyser when fault finding PCB's.