How to find the source of a burning smell in my computer?

Recently I find small unpleasant smell (like burning smell) from my desktop computer, not always, but from time to time. I don't know where it is from, but as I turn off the computer and sniff closely to individual hardware, esp the PSU, I can't find any smell.

I also took out the optical DVD drive and found a strong smell coming from it, but the DVD drive should still work fine.

I’d like to know

1. What can I do now?
2. How do I check the temperatures in my computer?
3. What is the normal range of temperatures?

Solution 1:

Use one of these

from a paper towel or toilet roll. If you stick your noise inside it while you sniff it makes your smell ability a lot more directional and makes it easer to narrow down what section of the computer the smell is coming from.

P.S. This also works very well when some part of your computer is making a noise and you can't tell where it is coming from, put the tube up to your ear and you can hear where the mystery squeal is coming from.

Solution 2:

3 things could go very hot: CPU, video card and power source. CPU temperature can be checked in BIOS. Video card GPU temperature can be seen in the driver's control center/panel (will not work for very old cards). As for the power supply temperature, in most cases it has no temp monitoring, you will just have to check how hot is the air evacuated from it. Normal temperature for a CPUs and video cards vary a lot by manufacturing era. Generally, CPUs should stay under 60C at load, just as old video card; the new video cards under 80C at load are fine (can even work correctly at 100C).