There are now two modifications to the PC23C video AGC circuit. The first and original "AGC auto/manual" mod is very easy to do but merely clamps the video ACG to the minimum value and prevents it from attempting to raise the gain if the overall video level drops. This is often sufficient to prevent overexposure, but it does nothing to raise the video level if the scene illumination is insufficient at the slowest available shutter speed.
During (so far unsuccessful) attempts to make the AGC peak-detecting, I discovered a second modification. This "AGC level" modification retains full AGC but causes the circuit set the level in response to smaller areas than an un-modified camera. It appears to result in video levels identical to the AGC auto/manual modification, but if the shutter speed cannot compensate for low illunation, the AGC will raise the video level to a maximum of approximately 30DB. This modification is recommended whether or not you do the "AGC auto/manual" modification.
Note that there are apparantly two versions of the PC23C being sold by Supercircuits. Both appear virtually identical on the outside and seem to perform identically as well. Unfortunately, the two cameras have different board layouts. Take a look at both versions and at your camera board and see which one matches your camera. While the "AGC level" modification may be done to either version of the camera since it is not dependant on circuit board layout, the "AGC auto/manual" modification is layout dependant and there are two versions of this modification.
AGC auto/manual modification, for "version 1" cameras
AGC auto/manual modification, for "version 2" cameras
AGC level modification, for "version 1" or "version 2" cameras