Through the site are examples of repairs that I have made to Sifrey Torah or M'gillot.  However this page looks explains some of more common repair needs and links to pictures and videos of real life examples.

One of the first things that you do is roll the scroll from end to end, looking as you go for obvious areas of problems, such as faded or broken letters.  However, sometimes you might also get a surprise when you get to the ends, as sometimes the atsey chayim are attached with string and not giddin, in which case the string has to go!

Faded areas or broken letters are often just a sign of age and constent use (occasionally I have seen people dragging the yad (pointer) tip across the letters and that breaks the ink. It is a pointer - so please point with it if you are a reader. Sometimes is can be a result of the chalky k’laf mashuach (coated parchment) which means the letters flake off giving a gritty surface to the letters.  Once rubbed down with an eraser or a clean cloth, overwriting is generally done with a more dilute ink, and is often quite difficult (harder than writing afresh) as you are pulling against old (gritty) ink.  In addition using full strength ink can make the letters stand very proud and look very black against the older ink for those letters that haven’t lifted. 

Please please please do not try to repair using ordinary ink or, as seen in one case, biro! 

Other areas may involve blotted letters.  This may have been caused by water damage where the letter is
lo k’tsurato (not according to it’s form) and is therefore invalid. 
   
Sometimes there are holes or rips in the parchment requiring patching (i.e. sticking a piece of k’laf from behind) can be used to reinforce the seams joining the y'riot (sheets) together, get rid of holes in the margins, straightening up margin edges where there may be tears and also to replace certain small sections of text which have errors and the k’laf cannot take the scraping out.  Unfortunately a lot of well meaning people occasionally use sellotape to reinforce or repair scrolls - it leaves an awful residue marking that it very difficult to get off and is not a valid means of repair. There are rules regarding patching and sometimes you just can't do it - e.g. if the rip goes through more thna 3 lines of writing. Also patching in an area involving God’s name is generally frowned upon as the patch might become loose and God’s name might fall off into a disgraceful area.  Hence since you cannot scrape out God’s name and you shouldn’t really cut out and patch you would need to replace the whole amud! However there is a very skilled scribe in Israel who can (and I have no idea how he does this) lift out with a scalpel the name of God intact on a very thin piece of the k’laf (near right) leaving clean k’laf underneath to write on!

Sometimes the reapirs are minor, sometimes they can very extensive indeed. below are some links to more information on repairs. Videos, facebook photo albums and a couple of my books that are particularly pertinent.