how to check capacitors on old PCB boards

[cloonypan]

Hello,

We need to check aged electrolytic capacitors on PCB boards to see if capacitances still available or not. Per some manuals of component testers, the methods to take actual characteristics of capacitors the capacitors should taken off from boards. Taking them off from boards troubles me. Once the they taken off from boards, they might not be weld nicely back to board. Therefore I am trying to ask if there any alternative testing methods. Thank you all.

 

[MacGyverS2000]

What's wrong with checking a known good cap while still on the board, then using that value (or take several measurements) as a nominal test spec for all other boards?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[cloonypan]

Hello,

The caps on PCB boards has already stored in warehouse orver five years. I am worried their capacitance still ok good or not. Therefore I would like to check their performances before those boards join into operation. I may provide some field pictures later.

 

[MikeHalloran]

If you have to warrant the product, just replace the caps and be done with it.


Mike Halloran
Pembroke Pines, FL, USA

 

[cloonypan]

Hi Mike,

I think I was stuck in this question.
Thanks for your solution. That's easier and cheaper.

 

[VEBill]

Take a sample.

Either test them In Circuit, or perform a functional test of the circuit card.

Five years isn't that long. It's likely that there's no problem.

 

[Skogsgurra]

While it is true that large 450 V and thereabouts capacitors need reforming after a few years on the shelf (see

http://www.vmars.org.uk/capacitor_reforming.htm

for an example). It is seldom necessary with capacitors soldered to a PCB.

The Al2O3 insulating layer deteriorates when the capacitors stay at zero volts and that increases the leakage current initially when voltage is applied. The Al2O3 layer is then quickly reformed when voltage is applied and I have necer had any incidents with small electrolytic capacitors - say 10 000 uF at 35 V or 100 uF at 350 V, the latter is common in old radio sets.

If you really want to make sure that there's no problem, I think that connecting those boards to nominal voltage for a while, say around ten minutes, will reveal any bad capacitors. But I doubt that you will find any.

An example: I do collect old radio sets and I have some from the thirties, fourties, fifties and so on. I was very careful when I switched the first ones on. Half the voltage, series incandescent lamp and all that. Never a problem. Nowadays I just switch on - even if it is a fifty years old set. And, again, never a problem.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[OperaHouse]

I doubt there would be any problem with boards five years old. The one exception would be if leakage of a capacitor would change the calibration of a circuit. In that case, powering the board for 15 minutes would reduce the leakage enough so it would be plug and play for the customer. If quality requirements require testing I would recomment an ESR test. ESR is probably the best indicator of capacitor quality. Other problems will also be reflected in ESR. In circuit is generally not a problem since the board load is minor compared to the ESR of the capacitor. If you search "ESR capacitor test" you will find many procedures that only require a signal generator and a scope

 

[RyreInc]

How old should a cap be before it should be checked/reformed then?

 

[Skogsgurra]

No general answer can be given.

"Power capacitors" are a much greater risk than smoothing capacitors and they are in their turn somewhat riskier than capacitors in RC filter applications, where the risk is zero.

Leakage currents reduce themselves when voltage is applied. Increased ESR is only a risk in power capacitors with high ripple current. And increased ESR cannot be reduced through reforming. If low ESR is important (like in SMPS and VFDs), all you can do is to test and replace. But increased ESR usually comes from operation and not from storage over long time.

The rest of the answer is: It depends. It depends on capacitor make, temperature and other things.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[sibeen]

Many years ago I used to repair SMPSs (anything to bring money into a struggling business) and I wouldn't have been without my Dick Smith ESR meter. Tested in circuit without an issue.


Dick Smith is an Australian electronics store that used to sell components and kits etc. Nowdays they sell TVs and stereos