Forgive me for chipping in very late in this thread, there are many good suggestions and you have to be very systematic about the process and not take short cuts or do too much work when you are very tired.
I looked at the manual on TekWiki with the file name Tek-466-early.pdf. Immediately before the schematic of the Power Supply is the diagram of power distribution between boards. This shows which of the multi-way connectors need to be removed in order to remove the +5V power to A3, A10, A7, A5 and A2 boards. If you remove all of these connectors and the +5V short remains when measured at the +5V supply then the fault is on the A6 board, this is the worst case with many places to look. Otherwise one or more of the now disconnected boards will show the short circuit on +5V and you have a much smaller area to concentrate on. If you find a short circuit on the A10 storage board and all of the capacitors measure OK with one leg removed then it is possible that one of the 74xx logic chips is the cause. I have found at least one case of this mode of failure but it is very much less common than failed capacitors.
Best wishes for your repair,
Roger
