Why pull and redo power transistors on the heatsink

[jstang]

Maggy's don't beat the crap out of amps.... thats the point.... And clipping ain't the same as power....amps clip at the same voltage with 16 or 4 ohms connected to them. The power at clipping into 16 ohms is very different than clipping into 4 ohms.... They need a current limiting circuit to limit power.... Blowing fuses does not mean you are using a lot of power.... What size fuse was it.... ?

I don't care about amp friendly, I care about running the amp til it got hot for proof of performance. Sure stuff a watkins woofer on that system and blow up the poor sui, I don't care it isn't mine. I know Magneplanars are an easy load to drive but they can take power, lots of power but not clipping. Had when I was selling gear in the 70s got another set 15 years ago and bought a lot of fuses.

Isn't a resistive load what they use to test amps? What is your point?

 

[jstang]

Relative is nonsense.... How did you mount the thermal couple....what kind was it.... Certified means almost nothing if Mounting of the thermal couple was incorrect....

Just one doc....check it out....

http://www.malcom.co.jp/en/pdf/tips_on_attaching_thermocouples.pdf

This is correct, and thanks. I didn't want to say anything, but I have access to certified, expensive temp measuring equipment for my job. I am well aware of accuracy and techniques to get relative measurements, as well as absolute measurements.

 

[Dingman]

I have access to a full materials lab if I really wanted to call in a favor. But I would not waste a favor like that just for this.

I would simply load the amp as for an FTC style preconditioning test, record the heat signature, then take apart, clean, and reassemble to spec with new grease. Then, rerun the test under the same/similar conditions.

That would be convincing enough for me to decide if it's worth it or not. I don't really care if anyone else changes their action or opinion about it. I just want to know if there seems to really be some meat here or if it seems largely just make work...with something more than forum anecdotes and theory.

Wow, you do have opportunity to do proper testing on this - I'm just a field tech myself. But ya, I was just looking for changes and my conclusion was that... I'll still refresh the goop if it's not a total chore.
Heh, I thought I was "pretty good" at getting thermal measurements, but you guys are obviously a step above me.

My test was just for the heck of it - like when I test components coming out and the ones replacing them - they all get measured (and I do keep my fingers off the components).
I think my test was valid - same conditions, same spot on the same bench. Same test equipment, with a film TC (I like those best). Not some silly infrared.
Same signal, with same power output as shown by RMS on my scope. It seemed valid to me for comparison.

 

[jstang]

Come on.... You guys are not even close to perfection....

If you want to play the "relative" game.... Just replace the compound and call it done....

I am not going let the notion of perfection stand in the way of more information. I know sometimes it's hard for Engineers not to get wrapped around the wheel in that regard but more data point are good as long as we have an understanding of what was done.

 

[jstang]

The devils in the details.... How about a pic of the TC mounting..... you may have had a good measurement.

If the TC was mounted correctly....Then the key is the condition of what was replaced, the old compound still may have been good.... Do you know for sure if it was ever replaced.....and how recently ?

Wow, you do have opportunity to do proper testing on this - I'm just a field tech myself. But ya, I was just looking for changes and my conclusion was that... I'll still refresh the goop if it's not a total chore.
Heh, I thought I was "pretty good" at getting thermal measurements, but you guys are obviously a step above me.

My test was just for the heck of it - like when I test components coming out and the ones replacing them - they all get measured (and I do keep my fingers off the components).
I think my test was valid - same conditions, same spot on the same bench. Same test equipment, with a film TC (I like those best). Not some silly infrared.
Same signal, with same power output as shown by RMS on my scope. It seemed valid to me for comparison.

 

[whoaru99]

Come on.... You guys are even close to perfection....

If you want to play the "relative" game.... Just replace the compound and call it done....

Relative is the key. If replacing the thermal compound materially changes the thermal resistance such results should be established by a before and after change in the heat signature.

 

[Mike Sweeney]

And here I thought caps could start a near religious war

Mike, how do you test the transistors, just the standard diode check or do you run them under power and get a graph?

I use one of the "fancy" ESR combo units (Peak) that can check caps and transistors. I don't have a way to run them under load and graph them. The checker gives an HFE number which in most cases is pretty close to published data sheets. I do check them out of circuit. It pretty much matches what the tester on my DVM says.. might even be the same circuit on the inside

 

[Dingman]

The devils in the details.... How about a pic of the TC mounting..... you may have had a good measurement.

The key is the condition of what was replaced, the old compound still have been good.... Do you know for sure if it was ever replaced.....and how recently ?

You are correct that I have no idea of actual condition of the original compound, and sorry, no pics of TC mounting. It was a film, into my Fluke and just taped onto the surface with electrical tape.

I'm not trying to prove a thing here - such a limited data set proves almost nothing and I don't think I even expressed an strong opinion based on this. I do think the nature of the test produced a valid result - for that test.
But really, a before-after measurement is just that - before and after. I stand by my "best practice" comment.

If I wanted to poke back at ya, I'd ask (and yes, I've glanced at your doc) how would we purposely cause an error of more than a couple of degrees with the same unit, same mounting, same space, same conditions? IMO, it would be pretty hard to fack that up.

 

[whoaru99]

Wow, you do have opportunity to do proper testing on this - I'm just a field tech myself. But ya, I was just looking for changes and my conclusion was that... I'll still refresh the goop if it's not a total chore.
Heh, I thought I was "pretty good" at getting thermal measurements, but you guys are obviously a step above me.

My test was just for the heck of it - like when I test components coming out and the ones replacing them - they all get measured (and I do keep my fingers off the components).
I think my test was valid - same conditions, same spot on the same bench. Same test equipment, with a film TC (I like those best). Not some silly infrared.
Same signal, with same power output as shown by RMS on my scope. It seemed valid to me for comparison.

That is basically the same plan I'd use, although as noted probably would use several surface mount TCs distributed between the output device cases and multiple locations on the heat sink.

 

[Dingman]

Relative is the key. If replacing the thermal compound materially changes the thermal resistance such results should be established by a before and after change in the heat signature.

This.

The only thing I think I could have done better is to run the two amps just below clipping. To be honest, I didn't have the balls to do that.

 

[jstang]

Absolutely correct, provided the testing was strictly preformed.... with proper TC mounting and knowing age/condition of the old replaced heatsink compound...

We now know that not to be the case.... The test was not conclusive.

Relative is the key. If replacing the thermal compound materially changes the thermal resistance such results should be established by a before and after change in the heat signature.

 

[whoaru99]

This.

The only thing I think I could have done better is to run the two amps just below clipping. To be honest, I didn't have the balls to do that.

I'd use 1/3 continuous rated power (sine wave signal). That is a very demanding operating point.

Frankly, it's probably not even necessary to push that hard for the experiment. We're just looking for a change in the heat signature, not trying to blow it up. LOL.

 

[whoaru99]

Absolutely correct, provided the testing was strictly preformed.... with proper TC mounting and know age/condition of the heatsink compound...

We now know that not to be the case....

I can certainly identify the age of the heat sink compound given the age of the amps and identify whether it is dry and crumbly or if still has some pliability left. The amps are untouched in regard to the original mounting. I picked them up more or less straight from the installed sound application. They'd never been opened prior to me blowing out the dust.

It will be a great bit of information if I get around to doing it. Again, I don't expect anyone will change their ways, heck that's not even my point. More of a Mythbusters sort of thing.

By all accounts, at the conclusion of the experiment you should be able to crow about how you told me so. I'm not worried about that possibility either, at least I'm asking questions and attempting to answer them.

 

[jstang]

You were close.... Very close.... your testing just needed a few tweaks and you would have been "Relatively close". Actually you would have been close enough.... The big issue was not knowing the age of the original compound or its condition...

Kudos for getting that close...

You are correct that I have no idea of actual condition of the original compound, and sorry, no pics of TC mounting. It was a film, into my Fluke and just taped onto the surface with electrical tape.

I'm not trying to prove a thing here - such a limited data set proves almost nothing and I don't think I even expressed an strong opinion based on this. I do think the nature of the test produced a valid result - for that test.
But really, a before-after measurement is just that - before and after. I stand by my "best practice" comment.

If I wanted to poke back at ya, I'd ask (and yes, I've glanced at your doc) how would we purposely cause an error of more than a couple of degrees with the same unit, same mounting, same space, same conditions? IMO, it would be pretty hard to fack that up.

 

[jstang]

I don't fear the details.... I relish in them... Relatively close is only good for horse shoes....

I can certainly identify the age of the heat sink compound and identify whether it is dry and crumbly or if still has some pliability left. The amps are untouched in regard to the original mounting. I picked them up more or less straight from the installed sound application.

Too bad that you seem almost to fear such information.

 

[jstang]

https://books.google.com/books?id=d...epage&q=thermocouple mounting methods&f=false

Somebody been there done that....but that might be over kill for us....

 

[jstang]

PC guys seem to be worried about it and they rarely last more than 6 years before getting trashed....

Oh by the way, never use PC Heatsink compound for audio gear.... PC compound is usually electrically conductive.... Bad for audio....

"Curing, Aging, & Cracking
There's a “curing process” with thermal compound – a time period required for the paste to reach its peak efficiency. When freshly applied, thermalpaste hasn't yet cured and is still somewhat liquid-y. It isn't until the compound has an aging period that maximum thermal efficiency is achieved. This can take a few hours or a few days, depending on load level and type of compound. Were you to thermally test your CPU immediately after application and then test it again a week later, the results should be marginally different. Not much, but enough to pick-up with accurate equipment and methodology.

Eventually, the thermal compound reaches and passes its peak efficiency, potentially spiraling downward into aging and cracking. Good compound won't do this within the average PC lifespan – diamond and silver compounds are a good example of high-endurance paste – but cheaper stuff (like silicone) will decompose with age. Under intense enough heat, the paste begins to crack and lose its ability to efficiently transfer heat from one surface to another.

Laptops are an excellent example of this process. A lot of our readers likely have experience replacing some sort of internal laptop component – a fan, the GPU's thermalpaste, reflowing the solder, or similar. Laptops undergo a lot of abuse, they're potentially exposed to external sources of heat (like the sun, if used outside), their ventilation ports are often smothered, the internals are predisposed to higher thermals resultant of a tight enclosure, the cooling abilities are relegated to smaller fans, and so forth. We've replaced laptop GPU compounds a number of times, normally because the stock compound has dried-up and lost its ability to adequately cool the silicon. During the replacement process, an astute technician will spot flakes of dried compound falling from the coldplate upon removing the heatsink / fan combo. This is aging."

 

[Dingman]

You were close.... Very close.... your testing just needed a few tweaks and you would have been "Relatively close". Actually you would have been close enough.... The big issue was not knowing the age of the original compound or its condition...

Kudos for getting that close...

Thanks man, I didn't mean to start anything.

 

[Dingman]

https://books.google.com/books?id=dKCFcp_YhjYC&pg=PA35&lpg=PA35&dq=thermocouple+mounting+methods&source=bl&ots=Nn03Rm-_wh&sig=K8UQPwXBqUSzHlnFvarVEYLDM2c&hl=en&sa=X&ved=0ahUKEwjOmrS8vcTZAhUGy1kKHaLHDno4ChDoAQgqMAE#v=onepage&q=thermocouple mounting methods&f=false

Somebody been there done that....but that might be over kill for us....

Ya, that's pretty detailed. Drilling a hole, and peening the edges? Heh, not for me. At least they do give you the option of soldering the TC to the transistor case, that's fairly reasonable.

And ya, mine are T-type TC's and I have the two kinds -welded tip and film tip.

Maybe I'll do more measurements on this 2270 I'm working on now. I do plan on applying new pads and goop. Just for fun, you know. Har!

 

[jstang]

One more.... what the hell, you can thank me for doing your google searches for you.... its all relative....

https://www.sciencedirect.com/science/article/pii/S002627141300139X

TIM = Thermal Interfacing Material = Heat Sink Compound....

"For high-temperature applications, the effect of the degradation of the TIMs on the thermal performance of power switch modules must be taken into account for ensuring long-term operation."

Again its Temp x Hours = aging.... its more than reasonable to replace the stuff after 45 years....