There is suspicion that the voltage regulators on boards 51 and 52 may be bad. These components are surface-mounted on the board with ball-grid arrays. The x-ray images below were made (by Debbie Salas, ISR-4) to see if there is something unusual about the BGAs. The image on the right shows part of the board layout, with the regulators in yellow, and the ball-grid pattern shown.
Board 17, part U28. This is a good board. Note the balls at the top are squashed into squares, whereas the ones on the bottom left are much smaller in this picture. We did not have an un-mounted part so that we could see how big the solder balls are before mounting.
Board 17, U26 and U28.
Board 51 (bad) U28 suspect. The grid balls look generally the same as for board 17, except some have 'bubbles'.
Board 51 (bad) U26 and U28
Board 52 (bad) U26 and U28
Board 52 (bad) U26 - left
Board 52 (bad) U28 - right