One thing to know is that parts were many times added to the bottom and even the top side of circuit boards by the engineers. They were making improvements or correcting issues that arouse. They couldn't redo the artwork and have new boards produced due to monetary issues so they had to use what they had. Many boards will have disc caps, resistors, diodes, jumpers, cut traces, etc. added to the boards. These are factory mods. I've seen many times when people have removed these, thinking they were added by someone and then rendered the radio inoperable or reduced its operability. The schematic often times did not show these factory mods, as only the original was released and revisions weren't. Sometimes the only way to know if they are factory mods is by examining the soldering. Do all the parts added look like they were all soldered by the same person? Many times you have to search for pictures or videos and hope to find a pic of the board to see if it has the same parts added. It may or may not, depending on when it was made. Usually the later ones will have the most parts added. I once had three Navaho 458s I was repairing at the same time, and every one had a different amount of disc caps on the bottom. They only made that version with the 858PLL for two years. The one with the lowest serial number had the least amount of caps, and the highest had the most. Since all the circuitry was identical, just caps added to the bottom for improvements, I add the extra caps to the earlier two so they would have all the improvements.
