I have a Sigma macro lens that had focus problems, sent it direct to Sigma who said the same thing about it being obsolete so they sent it back unrepaired. I kept searching around the only folks who said they could probably fix it was Camera Repair Japan in Peachtree Corners, GA. They not only fixed the problem but upgraded the firmware and returned the lens in what looked like brand new condition. I couldn't have been more pleased with the service. Unfortunately their website comes up as unassigned (www.CameraFix.com) so it's possible the pandemic wiped them out. The phone for them listed on my receipt is 770-849-0555, and that was valid just a year ago. I hope this helps.

Usually, when a zoom won't cover it's full range, it is a guide bushing (or loose screw that holds the bushing) that has come loose or come out of position. Maybe: the screw/bushing is the culprit (unless the lens has suffered a "hit" from being dropped, and actually broken something off). This is usually repairable, but varies in complexity from lens to lens. For starters you could google "Canon EF 28-200 repair", you will find some youtube videos and maybe/possibly even some schematics or repair manuals. A place that also has some service manuals is USCAMERA.COM (I've bought Nikon Factory Repair manuals "downloads" from them). Often you can service zoom bushings through service ports hidden under the rubber rings, or from the mount end/or front glass end...again, this varies from lens to lens/model to model. You will need some small electronics/camera specific repair tools...most are relatively inexpensive and easy to find. Don't use inappropriate tools, that could also make things worse.

Most of the manufacturers drop an older model from "repair" once they have depleted the repair parts made during initial factory "runs", excepting for those higher priced models, and they eventually stop making parts for those too. As someone else said, you'd probably be better off picking up another used model. You could turn yours into a "parts lens" as there are always folks looking for mounts, glass, rubbers, tubes, switches, boards, motors and such, especially if it still looks great, it will have some value.

If you do go inside the lens, try not to disturb the focus stack - I don't know how it is with that lens, but it is easy to "brick" modern focus stacks, and then you need access to expensive alignment equipment.

If you can still move the zoom thru full cycle by push/pull (Don't force it, you might do more damage), some folks just use them as a push/pull and continue on.

At any rate good luck with your quest, finding good info and factory manuals can involve some detective work. Later today I will look into that lens, if I can come up with more usefull info I'll come back or PM. Cheers

After discontinuation, at some point Canon runs out of parts to make repairs, declares an item obsolete and refuses to take them in for repairs.

Exactly when this occurs depends upon the product and how much stock of replacement parts remains after it's been discontinued. For example, the EF 200mm f/1.8L USM was made obsolete within a year or two after discontinuation because the parts supply ran out. On the other hand, it was possible to have an EF 300mm f/2.8L IS USM lens serviced and repaired by Canon for 7 or 8 years after it was superseded by the "II" model.

To a large extent this is just the nature of "factory" repair services. They don't go in and "fix" a failed component. They "replace" the entire module instead. And they only use brand new, OEM parts.

In contrast, an independent repairer might un-solder a sub-component and replace it with a generic or even a used one, if available. Sometimes independent repairers even make parts, when needed.

For example, over time and with regular use it was a common problem with the Canon 20D through 50D (at least) for the shutter release button to get "gunked up" internally with finger oils and dirt. The symptom of this was a noticeably increased shutter lag that got worse and worse until the shutter wouldn't release at all. If you sent the camera to Canon's factory repair department for a fix, they would simply install a new shutter release button. But all that's usually needed is a good cleaning and re-lubrication, which is what an independent repairer might do, saving the cost of any replacement parts. (In fact, for that particular problem there was a DYI cleaning that required no disassembly of the camera. But that wasn't ideal because it didn't re-lubricate the mechanism, was a bit risky and needed to be done very carefully).

In this case, Canon has declared the EF 28-200mm obsolete, which means they won't even take one in for possible repair. The only option is to have an independent repair shop look at it and give a quote. Since that's not a very valuable lens, it might be better to just try to replace it with a good, used one. If you can find one. (You might end up buying a lens with problems or little lifespan left).

Or look for something else that's similar... for example, the Canon EF 28-135mm IS USM is widely available used for around $100... a little more or a little less depending upon condition... and is a quite good performing "walk-around" lens. Although it dates way back to the days of film, it was often provided as a kit lens on DSLRs. As a result, there are lots of them around. It's image quality, autofocus performance and image stabilization rival that of some considerably more expensive L series lenses, though it's nowhere near as well built or sealed as an L. And, it's also been discontinued within the last year or two, so will eventually not be repairable or serviceable by Canon. (Independent repair may be possible, but may not be worth it on a lens that can be bought so cheaply.)

Of course, 135mm isn't 200mm. There is no Canon 28-200mm exact replacement now. If you need the telephoto reach a "premium" replacement is the EF 28-300mm "L" IS USM, which is a big step up in every way (image quality, IS, build quality, tripod collar and more)... not to mention an additional 100mm focal length. But, it's considerably bigger, heavier and a whole heck of a lot more expensive. It's still in production and can be bought new, but has been around for quite a few years (intro'd in 2004) and is widely available used.

I know this download says 28-135, but the construction may be very similar, will give you an idea of structure, with so so diagrams. However, I'm sure parts are tough to get (via donor lens) may not be worth effort beyond using it as a push/pull zoom, if that works with your lens. I have a 28-300 Sigma f/Canon that has a broken "strut" that moves the zoom via zoom rubber ring....can't get the part (could rob another 28-300, but, Meh) so I operate via push/pull of the hood....not ideal, but it works (and I rarely use the lens now...but i could if needed).

https://learncamerarepair.com/downloads/pdf/Canon-EF-28-135mm-f35-56-IS-USM-Parts.pdf

If you want another, I'm sure one will pop up for a reasonable price at some point, just make sure you have recourse in case of DOA or early fail (keeping in mind that these are not new lenses). MPB/KEH/UPP and others usually give 6 months on theirs. Good hunting!

Good luck with it. There is a series of Tamron lenses I like to buy every time I see one with a "jammed" or "broken" zoom. Almost all of them have been extremely easy to fix: remove zoom rubber, pull tape from little service hole, fish out the zoom guide screw and/or bushing, remount and add a drop of locktight, close back up, viola, perfectly fine again.... some others require removing the mount, but thats not to bad either. If I can actually find a manual or video for the 28-200 I'll send a copy or link.
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