thermal paste smell?

[PreSapian]

Just got a used naim nait 5i amp that starts smelling from the transistors once it's been warmed up enough. It's a sickly glue-like smell. I suspected it's the thermal grease, took a sample of it on a bare metal rod and scorched it with a lighter and got the same odor. Is it unusual for the grease to smell when it's being heated? and is the smell toxic? The amp has been used for a quite some time so we can rule out the 'new gear' symptom.

[Ian Finch]

Hi
Traditional white paste thermal transfer compound is silicone oil based which should be
odour free or of low odour and stable to at least 150 degrees C. Some compounds are
just oil + mineral such as zinc Oxide or the original, clear grease used aerogel silica, like
chemistry lab. stopper grease. These are all inert materials, with little odour at correct
transistor operating temperatures.

You have reason then, to suspect that these parts have been replaced using something
other than suitable paste/grease. If you can identify the odour, you may have worked
out the shortcut taken. It would not be the first time that someone burns his amp and
fixes it the cheapest way possible and then sells it. I have once seen facial make-up
used here, simply because they are white grease too.

OTOH, if it really was getting so hot to cause the odour to be obvious, you have far worse
things to worry about. It may be a lot of work, but you should at least remove the stuff
and use the right product from an electronic parts supplier.