Parts failure analysis

[wattsabundant]

I have some failed parts that have been disected.



The relay was pulled from a Marantz 140 after it had failed. The contact is welded together. This is due to the fact that the relay contacts are not rated to break DC.



An open 9800uf cap from a 700B. The positive post corroded off. note that the cap is smaller than the can. There is a tar that fills the void in the can. What happens if the tar is not there?



Two M\J15024 The one on the left is shorted. The one on the right is good. The left one has everything fused together. Note where the die is located. If using mica insulators the only place the grease has to be applied is where the die is located. The entire case does not have to be covered.

 

[CASSETTE DECK]

If using mica insulators the only place the grease has to be applied is where the die is located. The entire case does not have to be covered.

I always apply heat transfer grease to the entire surface area in contact with the mica washer to maximize heat transfer. Heat conducts away from the die to the rest of the TO3 transistor case.

 

[laatsch55]

I also have to question that Don. The die emits heat to the entire case, so wouldn't you want to make the entire case conductive?

 

[laatsch55]

ON the big cap, had the electrolyte volume decreased?

And the contacts on that relay look just like the ones out of the relay that saved my K's..

Interesting pic on the die, just melted into a blob. How much amperage would it take in that condition to blow open??

And if the tar is not there that's a pretty good connection to the cap case.

 

[wattsabundant]

ON the big cap, had the electrolyte volume decreased?

The elctrolyte couldn't be seen The paper was dry. It looked like there was corrosion on the positive post that eroded the connections

And the contacts on that relay look just like the ones out of the relay that saved my K's..

They're intendedd to be sacrificial

Interesting pic on the die, just melted into a blob. How much amperage would it take in that condition to blow open?? I could imagine 2-300 amps if there was a short in each half of the amp.

And if the tar is not there that's a pretty good connection to the cap case.

The tar fill up the void in the can. Without the tar the electrolyte lays in the bottom of the can if it is mounted horizontal. The cap opens up

 

[wattsabundant]

I also have to question that Don. The die emits heat to the entire case, so wouldn't you want to make the entire case conductive?

Next time you tear out some outputs look at where the paste is. Sometimes you see it just between the pins. Transistors like the 2sd555 had a raised area between the pins for improved heat transfer.

 

[premiumplus]

Next time you tear out some outputs look at where the paste is. Sometimes you see it just between the pins. Transistors like the 2sd555 had a raised area between the pins for improved heat transfer.

That's interesting...I always thought that the voids in paste coverage was just evidence of bad work.
Very cool pictures, Don. Keep up the good work!