OP

Quoted from ravve:

What could be causing the +5.10v coming from an external computer power supply, to drop to 4.37v on the MPU board, right at the power connector J210?
Board is a WPC 89, on the bench.
Voltage is not dropping on a specific chip or so, just directly on J210 which is the connector for input power (connected to computer power supply).
In short, voltage is 4.37v everywhere where it should be 5v.
Removed socketed chips one by one and measured voltage every time, none of these made difference: u4, u6, u13, u15-u20.
U4 and U13 gets a bit hotter than the others, but again I removed those and still measured 4.37V.
Also checked traces, resistors, diodes (in circuit).
Could a malfunctioned chip affect the whole 5v line on the board? Perhaps most likely another component like a cap?