We have some old CRT screens (we don't use them anymore, but didn't throw them away yet) that smell really bad when you activate them - why do they do that? I remember that this effect started relatively suddenly.

  • What sort of bad smell? Could be anything from dead insects/animals, to ozone to internal failures of many sorts.
    – Journeyman Geek
    Jul 26, 2012 at 13:29
  • 1
    @JourneymanGeek: Uh, I'm bad at describing smells. :( Hmm... a bit stinging... a bit like, uh... like dust and plastic?
    – thejh
    Jul 26, 2012 at 13:47
  • 3
    "like dust and plastic" So... this large surfaced object that probably sat for years in the same place, that has vent holes on the top of it, that most likely collected dust on top of and (thus through those vent holes) inside of it... now smell of burning dust and plastic when you turn them on. This should not surprise you, IMO.
    – Bon Gart
    Jul 26, 2012 at 14:43
  • No boom today? Boom tommorrow, always boom tommorrow. On the bright side, we may possibly rule out short circuits and dust explosions
    – Journeyman Geek
    Jul 26, 2012 at 15:25

1 Answer 1


The smell could be from the electrolyte of leaking capacitors. I recently solved that issue for some CRT front projectors manufactured in 1994. One day one projector would emit a mildew-like odor shortly after turn-on, and the smell would dissipate after about 5 minutes. During board swapping for another issue, I was able to isolate the source of the odor and replace the leaking capacitors.

Depending on the formula for the electrolyte, I assume the smell could be different for other capacitors. The leaky caps in the PJ were mostly small (e.g. 100uF 16V) Nichicon KME and SP.

The electrolyte is typically corrosive. So the electronics will eventually fail, either from a leaky cap or a corroded joint. Somekind of corrective action would be needed if you want to maintain the monitors.

Looking for leaking capacitors is not easy. The tops of the can were not bulging. The worst ones had a brownish stain on the PCB, almost like flux residue. You need to look for stains around each capacitor or discolored solder joints (on the component side of the PCB). An ESR meter did not reliably detect some leaky caps

There are solvents to clean boards, but they are typically considered toxic, e.g. 1,1,1-trichloroethane.

Of course, exercise caution when opening up high-voltage devices.

  • Hmm, this sonds plausible. :) Sadly, someone else here already threw the old monitors away, so I can't try it. :(
    – thejh
    Aug 3, 2012 at 11:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.