you probably had a broken Door-Spring

Not the spring but the rope.

http://www.managemylife.com/mmh/questions/134666-how-can-i-c...

The spring is... metal so it's not likely to have broken. The rope... has been known to break. The rope is routed over part key number 9 and attached to the door. With the lower access panel removed you can reach in and feel for the spring and rope link....
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We had the same repair done four or five years ago and the repair guy did it by feel -- I watched him and couldn't see what he was doing. That's when I decided I didn't want to tackle it myself if it happened again, not if I had to do it by touch. The rope that was replaced is Part #24 on the diagram at this link. I don't know if other parts were also replaced:

http://media.fotki.com/1_p,wkddfwdtkrwbkrtxgtqsskgwtqkq,vi/k...

Yesterday's repair guy said earlier replacement kits were made too cheaply or designed poorly so the rope rubbed on something and didn't last long - as we discovered - but this has been improved upon. No matter - if it breaks again in four years it will be a good excuse to replace the black unit with a stainless steel one that makes a little less noise.

--fleg