Zenith PRO 895x/900x

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This board has failed a number of times in various sets I;ve had in, and can cause a variety of problems, including low brightness or contrast, one tube that has no video information to it, or a ‘no picture’ condition:

While the Zenith service manual calls this board the Micro/Scan/RGB/Processor board, this board has the bulk of the H and V drive circuitry as well as all of the RGB processing circuits on it. I’ve had a number of failures on this board, and no failure seems to be related to the same parts failing over and over again, so each round of troubleshooting of this board is a new adventure. Some of the problems lie in the tiny SMT transistors that are used on this board. I replace the defective ones with larger standard size transistors which seems to make the boards more reliable.