@Spenser I am glad that you found this thread to be helpful in some way
And yes, leesonic's KA-7100 threads (and his others) are a great resource.
Thanks for responding to my inquiry and posting pics of your solution...hard to believe that 5 years has passed since I last posted in this thread.
I agree with your approach to prevent further warping of the board, but not attempting to straighten it back to original which might stress the solder joints as well as the board itself. Along that same line of thinking, going forward I will try not to remove the bottom cover of my KA-7100 at all, unless absolutely necessary. Because each time the bottom is removed it allows the board to flex just a little. And no, I don't know why the designers chose foam for support of those floating corners. But they would never have guessed that those units would still be in service 40+ years after they left the factory. The foam did do its job for quite a long time.
As for your support solution I have a couple of thoughts. The first one being that I am no expert, as this is kind of in the realm of mechanical engineering. I don't know how much pressure the PCB can take, or how much flex the solder joints can withstand, etc. I like that the old caps you used provide a lot of surface contact area to the PCB which, I think, could be a fairly brittle material. It appears that the caps may contact a track or two on the PCB. Don't know whether the track is ground only, or if some other tracks are also contacting the body of the cap. Being super OCD as I am, I would probably put a layer or electrical tape between the sleeve of the cap and the PCB. That may not be necessary if the plastic sleeve of the cap is intact, I don't know honestly. As far as the plastic stand-off, of course plastic is the preferred material for this type of application. I am not clear on the size or shape of the proposed stand-off, or its diameter. If the diameter of the stand-off was similar to, say the diameter of the #6 screw head in your pics, I would worry about pressure possibly breaking off the corner of the PCB. It may be that I am not fully understanding the concept.
Spenser, I do not know your experience level with soldering. Personally I would take a very close look, with a magnifying glass and (for me) a couple pairs of glasses, and good light, and from more than one angle....at all of the joints in the amp, but particularly the joints near the corners of that main board. Bad joints can be tricky to see. Sometimes a very subtle, easily missed halo can be a trouble maker. Looking at your next-to-last pic, my attention is drawn to: R46 (left side), R40 (left), R30 (left), Q12 (center), C18 (left), D8 (left), D6 (left). I can't say that any of those are bad, just that I can not tell for certain from the pic that they are good.
Hope you are enjoying your KA-7100. I just put mine back into rotation today after sitting for a few months to give someone else a turn.
