|The problem with the 90/91 boards is complete solder failure. They have a high amount of affected areas because of the use of many components and points on the board that connect the bottom layer to the top layer (plated-thru holes with and without components). The newer boards use three ICs that use fewer components and only one bottom layer of traces.
After realizing that even with the repair I was doing that included re-soldering the plated-thru holes without components may fail after a few years, I started putting component leads cut form the new capacitors I install through the holes and solder them to both sides to help insure a longer lasting connection.
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