Ecaps ,ESR meters , basic VI study on Led ceiling light driver PCB

Started by tracker, December 15, 2019, 02:15:10 PM

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Why this post ?
many requests from friends and newbies asking how to use ESR meters for faultfinding.
to highlight the instrument limitations and share my thoughts and workflow .

I use ESR meters to measure the caps precisely  in-circuit ....typically down to 0.05R
If the value looks odd , i  huntron it , to find out if there are any other components connected and interfering with it
It helps if you have 2 similar boards to compare the values.
Without schematics , comparisons are my preferred choice when troubleshooting .

I also use ESR meters to see the values out of circuit.
i use a model which measures both capacitance and ESR together. To check for bad caps before putting them into a circuit. Some suppliers may sell bad caps or caps which have been stored for a long time. There are date codes on some Ecaps.But testing them is the best way to know if they are good before putting them into a circuit.

Here is a practical exercise to learn more ...
Try this to learn limitations of ASA and ESR when troubleshooting .
Get a few ceiling Led light driver PCBs  .5 or 6 would be Good for studying Ecaps in-circuit.
If you have a tracker and ESRmeter, Use both on the ecaps. Those caps are in hostile environment (high temp) and  fail often .
You need to troubleshoot with power -off ( dangerous to probe components in power-on state)...advantage of  using Huntron power-off method when troubleshooting :)

This situation  is often what we are faced with when troubleshooting pcbs:-
No schematics.
Ecaps ,diodes,R ,IC, transformers connected together in- circuit .
Lots of VI combinations to "see" ( diodes+caps , diodes +R, IC+R ...)
Simple circuit to learn  VI  and easy to get 2 similar PCBs.
Easy to remove Ecaps and study performance issues (ie test bed to study manufacturer's claims on performance ).

Replace a few ecaps with higher quality ones and put lights back into operation. If lights fail ,you can see the failures....When you switch it  on/off ,it does not light or  Time lags ,means Ecaps are beginning to fail  or failed.
Test ecaps again.( In and out circuit with both equipment ).The ecaps should have increased in esr .Small increases can be seen by the esr meter but not with the huntron.
You should see the limitation of each.

If  VI signatures look the same , it should be good , safe to power -on the PCB.

In conclusion , know the limitations of your tools , spend your time studying which components fail and practice ,practice ,practice to improve your observation skills and you will be successful.

Happy troubleshooting .Repairing more  helps  the environment   :)


Agree with all you say.
My spare quite old Huntron PrpTrack developed some strange faults a while back.
I found all the electrolytic capacitors to be the 85 Deg. C type. And the ones nearest the heat from the  PSU had high ESR, leaked and in the process eaten away some of the copper track.
I replaced all the electrolytic capacitors on my two ProTracks with 105 Deg.C high ESR types.
My ProTrack now up and running doing its job!
Does anyone have a faulty ProTrack for spares, or a  06-3093 PROTRACK I DIGITIZER card for sale?


Good to know you find ESR tests useful.

Have replaced almost all the Tcaps with 50v ones ,near the centre of my protrack 20  pcb ,near the dc-dc convertors. Measured the outputs of the convertors which combine + and - 15v to give  30v for use by  op amps . When some of those Tcaps failed  on my unit ,they killed one dc-dc convertors (which did not have output short circuit protection ) Replaced both those dc-dc convertors with short circuit protection (from RS components )on the outputs .

Ecaps near the incoming Ac power supply too. All replaced ,Some have leaked ,not damaged pcb yet  but they were about to  .Since then ,  Protrack still working fine.
The unit needs extra cooling inside as it gets hot. Attached a computer fan on the outside ,sucking air out of vent holes.None of the ICs in protrack have failed so far .

Sorry No spare digitiser for sale ,all in use :)


Yes must replace the decoupling caps as well.
Sounds like your ProTrack is the same vintage as mine.
The new versions had a fan installed.
Only trouble with a fan is it sucks in all the dust as well!


Its KJ2  , without a fan at rear. panel. Have seen some decoupling caps fail ,but will replace  them all.Thanks for the advice .