4.7 on the +5v bus is too low.
The spec for TTL logic is 5v +/- 5% or 4.75 to 5.25v
Things start to get weird as you approach either limit... so check your power supply.
Next, if a CPU isn't working you must start with the basics - Power, Ground, Clock, Reset, Control Lines, and Address/Data busses.
Read the schematics and check for continuity on those lines from the CPU to the other chips on the MPU board. Patch any bad traces and test.
If all those traces are good then watch the reset line with a logic probe. When the board is powered up it should be momentarily low then flip to high and stay high. After that, look at the clock pin and see if you have a good clean clock signal. Then check the read, write, IRQ, and other control lines for proper signals.
If all that is working then check the ROMs for activity on the control lines (/CE and /OE) - keeping in mind that some systems ground one of those so check your schematic. No activity on the control line (that isn't grounded) means you need to check the address decoding circuitry. Those control lines need to be LOW for the chip to come active. If they are working then check the RAMs for address/data bus activity and for the control lines on them.
It's not hard to troubleshoot the older systems... but wtih all the acid damage you MUST double and triple check that the traces are good.
CONTINUITY TESTS DO NOT WORK IN ALL CASES. Use your ohmmeter and make sure you have close to zero ohms. My multimeter reads zero on continuity if the traces are less than 25 ohms in resistance. This can lead to problems. I had a Pac Man board on the bench a couple of months ago that refused to boot. There were a few traces reading from 9 to 20 ohms in resistance when they should've been almost zero. A few patches later and the board was working fine.
RJ