By LCD blemishes, I mean dark/dim spots on the display, specifically NOT including:

* broken pixels,
* dirt/stains on the front (outer) surface,
* backlight malfunction, or
* mechanical "pinch effects" (LCD response to pressure) such as are often seen at one or more corners.

The kind I mean are irregularly shaped blotches, usually with varying shading (gradations of darkening within the blotch). As someone who has bought a lot of used/refurbished Thinkpads over the years, I have seen these a number of times. I just got a T43 with a nice UXGA, but with a quite dark blotch shaped not unlike a candle flame, several millimeters tall.

Sometimes these seem to be dirt/contamination between the various layers, and sometimes mechanical dents (broad but not vary dark blotches with smooth gradation of shading). But I suppose there are other causes as well.

I would be grateful if any LCD gurus on the forum can advise about:

* diagnosing the cause of blemishes
* if it is practical to fix them, how to do it

Thanks!

Without seeing a picture of the actual blemish, I'd guess it was dust based on your description. FWIW, I have never seen anyone here report success in attempting to 'fix' that. I recall one post where it was attempted and failed. Assuming it could be cleaned, the major factor in taking an LCD that far apart is introducing more dust.

If the "candlelight" effect is in the corners of the screen, that's a backlight past its prime, extremely common on ID Tech UXGA panels.

If not, I'm with Harry...attempting to remove dust specs will likely have a destroyed panel as the end result.

I've only seen this once, on a used LCD screen I bought from eBay. My guess is that someone pressed their thumb really hard against the screen, causing permanent damage