Below is the corrosion and fix on my A600:
There is a trace under U17 that is broken so a temproary wire jumper was put in.
With the wire jumper removed. I can confirm that both U5 (Gayle) and the two U16 and U17 stay cold even after about 5 minutes of boot looping. Eveything else was relatively warm.
Even when OK (with wire jumper put back in), on the insert disk boot screen, it was the same symptons - cold U5 (Gayle) and the two U16 and U17 and everything else was relatively warm.