Video Problems: RGB Output Amplifiers

Each CRT has an RGB output amplifier, and with all models post 1990 (Barco 500 and 800), they are located on or near the CRT socket. The Barco 500, 800 and 801 sets have three identical RGB amplifiers screwed to the chassis with two screws, and are located directly over each CRT socket. The Barco 500 and 800 RGB amplifiers failed regularly and can cause faint diagonal lines across one tube face (called ‘retrace lines), or worse, can cause spot burn at shutoff on the tube face. Fortunately the failure of these boards occur over time, so if you notice a small dot at turnoff of a Barco 500 or 800, do not continue to use the set. Send those boards in for servicing immediately to prevent spot burn.

The Barco 801 and 808 had newer video output boards that used chips rather than transistors that overcame the spot burn and retrace line problems of the earlier models. These chips run hot however, and failure of the chips can occur. Typically the CRT tube goes dead when the chip fails.

Late model Barcos had the CRT socket and video output amplifier circuitry combined right into the CRT socket assembly. Sets with Sony tubes have a thick red focus wire that goes from each CRT socket to the G2/focus board. MEC tubes do not have this wire.

Since all three CRT output boards are identical, it’s easy to determine a potential fault with a board by swapping CRT sockets or boards with another tube. If the problem moves to another tube, the problem is in the CRT socket or board. If the problem remains with the same tube, then either the tube is at fault or the video driver circuitry is defective.

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