Hi to my many friends,
this story involves local Sydney electronics maker Jands, a few years ago.
I know Jands quite well, been to their factory many times.
I know the particular amplifier, the SR3000, rated at 1500W per channel on music programme.
I know the designer, Doug Ford - he has since appeared on U-tube.
See pics of culprit amplifier:
Doug appears here, the talkative one on the left:
An SR3000 turns up on my bench, just out of its one year warranty.
One channel has failed, many blown MJ15024/5 TO3 devices and TO220 drivers. I start removing the shorted BJTs and then stop - pick up the phone and dial Doug.
Hi Doug, tell me why are you using axel grease instead of thermal compound in the SR3000 ? The grease under your TO3s has boiled away and spread itself all over you nice red heatsinks.
Bullshit !! We have been using the same *thermal grease* for years ( names local supplier ) we have a gallon can of it labelled thermal grease.
I don't think so, that is very thin clear Silicone with no filler, only used for lubricating bearings and such.
No way, I will go get the can and call you back - OK ?** 45 minutes later .....
Doug:(now much quieter)
Bloody heck, you were right Phil, the can is labelled Silicone Grease Lubricant. Fuck knows how we got supplied the wrong type, must have been years ago and the people here kept re-ordering it.
I checked with our service department, they have a private stash of heatsink grease with blue coloured filler used for repairs. First time I ever knew about that.
I can see how with no grease left, some devices would overheat and fail.
I already ordered genuine heatsink compound and should have it delivered tomorrow. Shit, we are gonna have to strip all the amps here now on soak and re-grease them.
Thanks for the information.
The red anodised heatsinks you see in the SR3000 pics are mounted on a PCB and operate live, with no insulators under the TO3s.
They are quite small and rely on powerful fan cooling.
The amp uses 4 x DC supply rails, +/-75V and +/- 150v so needs multiple heatsinks.
It took a while and some hot weather to remove the last vestiges of axel grease, so few came under the makers 1 year warranty.
That the service guys ( same building ) had a secret stash of the proper stuff is interesting.
I had been using normal, ZnO filled white grease for decades.
Jands never used it until after that phone conversation.