If you are interested in having a look inside a CS80, Prophet 5 Rev 1 and a Juno 106, then have a look at this video:
Prepare for a long but interesting video!
Anthony Marinelli has played all of these synths and wants to know what lies inside them, so he visits Rob Rosen who repairs and refurbishes synths. One thing I found very interesting to see is that the Prophet 5 Rev 1 because of stability issues got some buffering ICs added on the PCB. Because there was no more room, they were glued on the back of other ICs and wires were used to connect them to the signal sources they were supposed to buffer. Have a look at t=1:02:00 Rob explains that even in revision 2 you would see this. So if you have to spoil your PCB by adding a small circuit or some wires to it to solve a problem you encounter after building your module, don’t fret, the pro’s had to do that as well, now and then.