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The KCS28 to KCS40 RCA chassis' have a two stage DC coupled video amplifier from the second detector to the kinescope. This gets rid of the D.C. restorer diode from the earlier RCA designs. Note how the two stages are DC stacked. This means that the power supply voltages are more critical in these sets if you do not want bias the CRT on or off to heavily.
First check the bias on the kinescope: you'll likely find it biased off. Then next check the power supply voltages against the schematic. Note the resistive divider to provide the voltages. If you haven't gone through most of the decoupling capacitors yet, you'll likely find one pulling down one of the supply voltages in the chain.
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