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leaky/bad component detection......questions

R

rhinofly

Toadfather
What is a "leaky cap" and how does a person find them?

I guess what I really want to know is any tricks or technics people have for going through a piece of gear and checking for caps/resistors/transitors etc that are failing or only partialy working.

Is there a way to do this without desoldering each item?
 
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With the device in the circuit sometimes you can tell by look, feel for heat, smell the smoke, etc. Normal looking ones sometime simple measurements can spot the bad device. You really have to know electronics to trouble shoot... there is not enough room here to go through it all. Two years of technician training in a junior college is a good start :) .
 
Ill be damned. Leaky as in dielectric fluid leaking out of the cap. I thought it meant leaking electric charge. I have heard people refer to leaky transistors as well. Surely that is a different use of the word?

I have seen caps that look like that in my own gear. I thought it was just glue or flux or something left over from the manufacturing process.

Well that sure is a good place to start.

What about transistors? Anyway to tell via direct measurement if a trany is bad?

Awsome photo thanks:) Anyone else have pictures of bad "parts"?
 
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leaky - usually applied to a capacitor in which the resistance has dropped so far below normal that leakage current flows.

leakage current -an undesirable small value stray current which flows through an insulator or the dielectric of a capacitor.
 
Yes this is cap guts:p:
it s very corrosive and dangerous
if you are interested by others internals photos see this link
this guy is a japanese specialised in Vintage hifi repair and he takes photos of his repair.It s very interesting (the site is in japanese :) so use altavista)


http://www55.tok2.com/home/ja1mdn/index.html
 
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>it s very corrosive and dangerous

This old memory is dropping bits. Some old capacitor has ??? PCP?? PCT?? or what ever , which is cancer causing stuff.
 
>it s very corrosive and dangerous

This old memory is dropping bits. Some old capacitor has ??? PCP?? PCT?? or what ever , which is cancer causing stuff.
 
Well, in most cases the brown gunk at the bottom is a glue to hold the caps in place while the boards make their way through the assy. process The stuff very commonly becomes conductive over the years and if the unit is disassembled, it should be removed...I use a tiny wire brush on my Dremel.

Usually, a 'leaky' cap is as Vintage_Stereo suggests...it is leaking current from positive to neg. So it doesn't filter as it should and voltage drops easily under load.

Leaky transistors provide poor gain and upset DC balances in a circuit...measuring DC voltages around the board and comparing with expected values usually will ferret out bad transistors.

Resistors are usually pretty reliable devices, but again, measiring voltages and comparing with expected values will point you in the right direction.
 
it s very corrosive and dangerous
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The item is called PCBs. Was used in insulating gels and oils for many years.

Was phased out starting in the late 70s. Every time I turn in a X-ray tank it has to be tested for PCBs just to make sure.

In some large transformers the oil was replaced by Hexaflorothane gas. Not as good and lost all of the heat transfer properties.

PCBs are not to messed with. alot of us found out the hard way about the dangers of the chemicals used in the 50s-70s.

We will not even get into ETO. :(
 
Well I am confused. It sounds like the only way to identify a bad item (one that isnt in some way visually obvious) is to measure voltages on the board and compare to whats on the schematic. Then trace down anomolous measurements by desoldering suspect items and testing them off board?

Sorry...I am new to this. I understand electrical theory quite well...but have almost no practical experience troubleshooting and fixing complex electronics like audio gear.
 
Well (and don't take this wrong...) it isn't often you open up an amp and see the failed component waving a white flag of capitulation. ;)

It takes some practice and common sense to do this...along with a good meter, a service manual, a signal generator, and a scope.
 
Originally posted by rhinofly
Well I am confused. It sounds like the only way to identify a bad item (one that isnt in some way visually obvious) is to measure voltages on the board and compare to whats on the schematic. Then trace down anomolous measurements by desoldering suspect items and testing them off board?

Sorry...I am new to this. I understand electrical theory quite well...but have almost no practical experience troubleshooting and fixing complex electronics like audio gear.
Click to expand...

That is almost exactly how one goes about it. One missing step in the process is understanding first how the circuit is suppost to work and then making measurements to isolate the stages between the functioning ones and the defective one. One has to have an expectation of what to expect to have a good chance of finding a measurement that is off. Most stages have a signal goes in and a goes out along with DC bias and supply requirements. Stereo stuff can be a lot easier in that you probably have a good channel to compare measurements with. Typically the DC power circuitry is the only thing shared.

Troubleshooting is fast becoming a lost art as most new equipment is designed for module removal and replacement or to be non repairable in the first place. Component level troubleshoot requires a lot of training and experiance and not everyone enjoys the challenge. Repairing electronic problems is pretty trival really, just replace the bad component(s). Knowing which component(s) need to be replaced, now that is the trick. ;)

I have always enjoyed the challenge and have had a rewarding work history doing just that. Not everyone's head is 'wired' right to be real effective at it. A mental trick I have used often is to 'become the circuit', that is try and assume your are that circuit and figure out what you need to work. Do I have a DC current suppy? Do I have a output path, etc.

Some useful tips?

Spend plenty of time first accurately defining the symptoms of the problem. If more then one symptom, which is the more basic symptom.

Assume there is only one problem, and repair it one problem at a time.

Assume nothing is good, test it to prove it's not bad. I once had a 5 amp fuse that had somehow developed like 10 ohms of internal resistance! Now that one had me for awhile...:dunno:

I still cring when I read sometimes where someone is going to go in and replace every cap and resistor in a device. That is a very ineffective way of repair in that it takes lots of time and money and one seldom learns anything from the experiance.

OK, ready? go find something broken and start troubleshooting it :uzi: :uzi:


Lefty
 
Lefty, You know what it's called. Shotgun it!! I had one of my Military techs ask about a problem with an item that I knew inside and out.

I told him to replace this,this,that and that thinking that I would get him to think about what he was doing. Wrong....

My boss comes up to me and said: Sgt XXX says you told him to order all this stuff?

I had to go back to him and tell him what was going on. I was trying to get him to think about it.

They told us years ago that we would become nothing more that tube changers in time and I almost believe it.

Troubleshooting is fast becoming a lost art............
 
Originally posted by Lefty

OK, ready? go find something broken and start troubleshooting it
Click to expand...

Heh I am working on it. But so far the two vintage recievers I found have nothing wrong except for dirty pots and some blown bulbs.

Though I suspect that the 9090db i found might need a tuner alignment. I guess I could give that a go when I get the schematic:)



These things really are build like tanks.
 
>We will not even get into ETO

This is a new one to me. What was it use for and am I likely to find it in electronic stuff?
 
SolderIron. Sorry for the confusion. You will not find any ETO in your audio gear. It is a gas that is still used today to sterilize medical equipment that will not handle steam sterilization.

I have been repairing medical equipment for 23 years. It is now known that ETO causes alot of medical problems down the road.

In 1980 the exposure limit was 500 PPM continous. It has dropped over the years to 1 PPM Time weighted over 8 hours.

I have been drenched in this Cr#p and the worst blow came in 1989 when I tried to have another child and could not. ETO was the cause.

:eek:
 
EchoWars. Do not worry. There are other things the good ol Army
did to me. Have been fighting the VA for years. Not bitter as I still work for them but lets just say when I got out in 92 they told me:
You have Hep-C do not give blood, Have a nice day!!!:uzi: :uzi:

1980-1992 1-BS, 6-ARCOM, 5-AAM, 1-JSAAM Many others. DS vet.

It will all come out in the end..............
 
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