I have budjet meter - this one - TS-M8N

Now i have LCD monitor which is half working and am sure that after replace all electolytics on power/inverter board everything will be okey.

Can i measure capacitors without desolder and trust in ESR meter values?

thanks

 

Depends on the meter and its measurement technique. Its manual usually
states if it can do in circuit testing.

Also some meters have/do not have charged capacitor protection, so check
the manual. If you are not sure discharge any caps before measuring.

Regards, Dana.

 

I have budjet meter - this one - TS-M8N

Now i have LCD monitor which is half working and am sure that after replace all electolytics on power/inverter board everything will be okey.

Can i measure capacitors without desolder and trust in ESR meter values?

thanks

The ESR meters I’ve seen use a pulse voltage below 0.6V. That’s below a diode drop so it’s less likely to cause conduction. But there could still be resistance in parallel with a capacitor under test, and that would interfere with the measurement. This would tend to lower the reading, though. If you find a high reading, it shouldn’t be a false indication of a failed cap.

 

Depends on the meter and its measurement technique. Its manual usually
states if it can do in circuit testing.

Also some meters have/do not have charged capacitor protection, so check
the manual. If you are not sure discharge any caps before measuring.

Regards, Dana.

If the meter is like the one in the attached manual it has _no_ protection against a charged cap.

 

The one I built has a degree of protection - there is no DC path for discharge. However the capacitors I used may or may not have a voltage rating above the possible charge on a test cap. More of my ESR saga.

 

I have budjet meter - this one - TS-M8N

Now i have LCD monitor which is half working and am sure that after replace all electolytics on power/inverter board everything will be okey.

Can i measure capacitors without desolder and trust in ESR meter values?

thanks

Most in circuit test ESR meters use a test voltage low enough to miss silicon PN junctions - but maybe not Shottky Barrier junctions.

You have to know what ESR values are acceptable for the readings to mean anything anyway.

In PSU output filters - dodgy electrolytics tend to run hot.

 

Filter caps in switchers tend to go from rising ESR due to "wearout" to ruptured in pretty short order. The ripple current flowing through the ESR can generate a lot of heat (and grossly excessive ripple voltage). In electrolytic capacitors, temperature due to ESR has a greater life-shortening effect than the same ambient temperature. ESR is often by far the most important selection criterion for filter caps in switchers and with conventional aluminum caps it is not uncommon to use ten times as much capacitance as required just to get the ESR down.

I've repaired lots of switchers with multiple outputs. I look for any sign of bulging or overheated caps (latter sometimes revealed by the insulating sleeve slipping or splitting). If I find one that looks bad I replace the lot. I have never bothered to measure ESR, though it would be probably be worthwhile if doing regular preventative maintenance.

 

Filter caps in switchers tend to go from rising ESR due to "wearout" to ruptured in pretty short order. The ripple current flowing through the ESR can generate a lot of heat (and grossly excessive ripple voltage). In electrolytic capacitors, temperature due to ESR has a greater life-shortening effect than the same ambient temperature. ESR is often by far the most important selection criterion for filter caps in switchers and with conventional aluminum caps it is not uncommon to use ten times as much capacitance as required just to get the ESR down.

I've repaired lots of switchers with multiple outputs. I look for any sign of bulging or overheated caps (latter sometimes revealed by the insulating sleeve slipping or splitting). If I find one that looks bad I replace the lot. I have never bothered to measure ESR, though it would be probably be worthwhile if doing regular preventative maintenance.

I start by replacing the ruptured caps - that seldom completes the job.

Run it up and see which electrolytics get hot, if they're not causing trouble now - they soon will!!!

ESR testing is a waste of time if you don't know what are acceptable values.

 

"ESR testing is a waste of time if you don't know what are acceptable values."

Most definitely.

I spent far too much of my life becoming intimately acquainted with capacitor ESR and all the issues surrounding it. I have taken a vow to never design another SMPS as long as I live. I hate them with a passion (I never got to do any nice simple little ones with fixed input and output voltages, it was always something oddball - which of course is why they were custom designs instead of off-the-shelf). Cripes I hate them. Which reminds me - again - I really must do something about getting rid of about 20 or 30 kilograms of assorted capacitors for switchers - not to mention ferrite cores and powdered iron cores and wire and foil and bobbins and FETs and diodes and ... But the snow and ice are melting and it will be cycling season again and I'll put it off again.

 

1) most of all ESR measurers are built with very small output voltage, ca 60 mV or 200 mV - any of it may not be able to open any p-n barrier, even the germanium not. Thus, if only believe that capacitors are FULLY (!!!) discharged, then go on. That is VERY handy tool with which to identify the reason why the old pcb have given a defect.
2) no, the most of readings are indeed in format +/= 0,1 or even 0,01 Ohm, but if I have three different (Chineese) devices, I have three different readings. For example 0,2; 0,3; 0,4. Do You bother of it if the aim is to find out one cap with 150 Ohms? Just to have a metrological accuracy it isnt an aim in this application.

 

1) most of all ESR measurers are built with very small output voltage, ca 60 mV or 200 mV - any of it may not be able to open any p-n barrier, even the germanium not. Thus, if only believe that capacitors are FULLY (!!!) discharged, then go on. That is VERY handy tool with which to identify the reason why the old pcb have given a defect.
2) no, the most of readings are indeed in format +/= 0,1 or even 0,01 Ohm, but if I have three different (Chineese) devices, I have three different readings. For example 0,2; 0,3; 0,4. Do You bother of it if the aim is to find out one cap with 150 Ohms? Just to have a metrological accuracy it isnt an aim in this application.

Various forums on the Bob Parker ESR meter suggest an inverse parallel pair of rectifier diodes across the front panel sockets. The later revision of the Peak Atlas instrument has some form of built in safe discharge device - meanwhile; I won't be lending my older model Peak instrument to anyone.