Video AGC auto/manual modification to PC23C
(version 1)

The following modification has been "developed" (hacked is a better word) by me by trial and error (can't get a schematic out of Supercircuits) and prevents the video gain on the camera from rising as image intensity falls. By probing the circuit board, I have discovered that grounding a particular point on an unidentified component clamps the video gain at essentially "unity". Since the imager itself still controls the shutter speed, the result is that images are much more correctly exposed, without the decrease in signal to noise ratio caused by boosted video gain on small bright objects. At prime focus on my 8" f10, I need no filters at all, and the resulting images of (so far) the moon and Mars are well-exposed.

The camera is in three parts (kinda reminds me of Latin 101.... sorry). The front and rear castings are attached to the center sheet metal with a couple screws at each end. Remove the ones from the front, and the camera will separate with the front casting loose and the enclosure still attached to the rear casting. Using the sketch below (only the central area of the board is shown for clarity) locate the yellow wire running from the rear circuit board to the front circuit board..... and the component to which the yellow wire will be re-attached. These will be found on the side of the front imager board that is exposed when the case is removed. Merely (carefully) un-solder the yellow wire from its current location and re-attach it in the position indicated and you're done.

Following modification, the shutter switch becomes the video gain boost ON/OFF switch, while shutter speed control remains in AUTO exactly as if the modification had never been made and the shutter switch was left in the ON position. In other words, the camera will operate exactly as before if the shutter switch is in the ON position. However, with the shutter switch in the OFF position the shutter speed is still automatic, but the video gain is prevented from responding to scene illumination.

I have also band sawed the case on my PC23C to shorten it and allow it to swing through the forks of my LX200. Unfortunately, I still need to shorten it another 1/2"!

"Shorty" my band-sawed PC23C

"Shorty" my band-sawed PC23C, from the rear

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