If a cap goes, what usually happens? Same for resistors?

[canidoit]

I am just wondering, if you place a bad capacitor or a capacitor that does not work anymore, what usually happens? Does it make the unit not work but not damage any components around the bad cap or does it damage components surrounding the cap?

Same for resistors. I would like to know whether it is worth the risk using second hand, nos or vintage components for DIY builds.

 

[ColinS]

Generally caps fail in one of 2 ways....
1. Quietly, they get fat and just stop working...usually because of age or prolonged exposure to heat.
2. Loudly, with a bang and spray their electrolyte all over the rest of your board. This is unpleasant and smelly. Usually due to wrong polarity or over-voltage.

Electrolytics, plastic film and ceramic disc caps usually fail to open circuit and in most cases don't do any further damage to whatever kit they happen to be in at the time.

Tantalum caps 99.5 times out of 100 fail to a dead(ish) short and in some cases this can result in bad stuff happening to the rest of the circuit they are a part of.

It is a good idea to do a thought experiment about what happens in either case then decide on risking recycled parts, or something brand new.

For the ultra paranoid an ESR meter is essential for testing for deadness in capacitors.

Resistors usually last forever, if they get too hot they burn out, the smoke escapes and they stop conducting anything.

Before changing caps or resistors it is worth checking to see WHY they have failed. If the bit of kit is quite old and has been powered on for most of it's life, then it is usually safe to assume that all the electrolytic caps have dried out and will need to be replaced. This is almost worth doing as a matter of course after 10 or so years of heavy use. This rule may not apply in 10 years time.... Look to see if they're getting fat, this is a sign of old age and impending death in capacitors

Does this help?

C

 

[CJ]

Tants will explode if run backwards,

lytics will look like a steam locomotovie, for a lil while,

old plastic molded  color banded tubulars start to pass dc, (they get leaky)

ceramic never fails,

oil caps do not get used nowadays,

i guess exploding PCB's are out of style,  ;D

resistor?

they  torch your pc board, so go point to point.


tropical fish caps float on their sides for a while, then sink to the bottom.

just like JFK Jr. 

 

[canidoit]

Generally caps fail in one of 2 ways....
1. Quietly, they get fat and just stop working...usually because of age or prolonged exposure to heat.
2. Loudly, with a bang and spray their electrolyte all over the rest of your board. This is unpleasant and smelly. Usually due to wrong polarity or over-voltage.

Electrolytics, plastic film and ceramic disc caps usually fail to open circuit and in most cases don't do any further damage to whatever kit they happen to be in at the time.

Tantalum caps 99.5 times out of 100 fail to a dead(ish) short and in some cases this can result in bad stuff happening to the rest of the circuit they are a part of.

It is a good idea to do a thought experiment about what happens in either case then decide on risking recycled parts, or something brand new.

For the ultra paranoid an ESR meter is essential for testing for deadness in capacitors.

Resistors usually last forever, if they get too hot they burn out, the smoke escapes and they stop conducting anything.

Before changing caps or resistors it is worth checking to see WHY they have failed. If the bit of kit is quite old and has been powered on for most of it's life, then it is usually safe to assume that all the electrolytic caps have dried out and will need to be replaced. This is almost worth doing as a matter of course after 10 or so years of heavy use. This rule may not apply in 10 years time.... Look to see if they're getting fat, this is a sign of old age and impending death in capacitors

Does this help?

C

Thanks mate. Great insight.

 

[emrr]

The thing to think about is what happens to current draw for various failure states.  And where any additional current goes.  Or, if less current, what that does to voltage figures in terms of rise. 

 

[Chuckles]

I used to salvage parts but new parts are cheap enough these days that it is not worth the risk.

That said, resistors made since 1970 that look fine will be OK. Ceramic capacitors rarely ever go bad. Electrolytics made since 1990 should be just fine.

 

[lassoharp]

That said, resistors made since 1970 that look fine will be OK

I've checked many carbon comps from 60's and 50's that were spot on and not creating noise problems.  I'd distinguish as low stress vs high stress as first tier of resistor evaluation.  Even low current resistors can get heat stress from proximity over time.

 

[JohnRoberts]

I am just wondering, if you place a bad capacitor or a capacitor that does not work anymore, what usually happens? Does it make the unit not work but not damage any components around the bad cap or does it damage components surrounding the cap?

As already posted caps can fail in different ways, slowly by losing electrolyte so failing harmlessly open circuit, or suddenly as a short circuit. The short circuit failure mode can cause problems in associated components. For example a large electrolytic in a power supply that short circuits can draw excessive current in diodes/transformer winding and damage other connected parts.

Same for resistors. I would like to know whether it is worth the risk using second hand, nos or vintage components for DIY builds.

Resistors generally fail as open circuit from over heating. Often you will be able to see discoloration from the excess heating. They make "flame proof" resistors specifically engineered to not start fires when overloaded.

In general modern components are always better. Most components are pretty cheap in comparison to the cost of your time and labor to troubleshoot faulty or out of tolerance  components.

JR