Here you see IC23, outlined in yellow, on the Korg Poly-61's CPU circuit board.

This is the faulty chip preventing the synthesizer's envelopes from working properly.

A closer look showed that the nearby transistor, Q4, was missing one of its leads.

This transistor is only used when a footswitch is plugged into the Release jack on the rear panel.

Apparently, battery acid leaked onto this board at some point and ate away the transistor's emitter lead.

In this photo, both Q4 and IC23 have been removed.

Also, notice the damage to a circuit trace near the photo's upper right.  We tested the continuity of this trace and found it to be good.

We cleaned this area of the circuit board with a strong solvent (MEK) to neutralize any remaining contaminant.

Here you see the foil side of the circuit board after the parts have been removed and the solder pads cleaned.

Here is the newly installed IC socket.

Sockets are used in case the IC ever needs changing again.  Solder pads and foil traces can be damaged by too much reworking.

For details on how to remove an IC and replace it with a socket, check out this repair story.

Here you see the new 4558 op-amp and the new 2SA733 transistor installed.