The SR560 is a workhorse of a preamplifier, but it is sensitive, and easy to put in to an overload condition. Thankfully, it was well designed and is easy to repair.
First, a copy of the manual is available here:
On page 17, you can note that the most commonly damaged component is (U106, National Semiconductor Corp. P/N NPD5564). A unit displaying a persistent overload that cannot be cleared should have this part replaced first.
So, that's what I did.
The first part is sourcing the replacement. NPD5564 is obsolete. I had to order a replacement off Ebay ($4 shipped). All of my local supply stores acted like I was a fool for wanting something without a valid NTE cross ref number.
(note red indicator on picture, showing persistent overload)
Step 1: Step 1, Unplug and Take Apart Amplifier
Second, you should be working on a static free work surface of some sort...or at least discharge any static electricity prior to working inside of the instrument.
Really straight forward. There are four screws that you have to take out, phillips head. They are on the sides of the instrument, and on the bottom access panel. (the top access panel is where the batteries are stored)
After removing the screws, you need to remove the access panel. You should have something that looks like the picture below.
Step 2: Replace IC and Reassemble.
The part you are removing and replacing is the 8 pin IC immediately to the right of the yellow part that is the furthest to the right of the group of four of them in the bottom left hand of the picture. That was a mouthful!
After replacing the IC, you can replace the bottom cover. Mind didn't want to line up perfectly and needed a little bit of love to get the holes aligned properly.
Step 3: Test!
(sorry for the crappy picture)