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Well, in lookin' at the schematic, the contrast control appears to be a manual (not automatic) gain control, varying the negative grid bias on the IF tubes. Low gain would indicate the control voltage is too negative.
The control pot is supplied with a negative voltage thru R44 (2.7K), and the other end of the pot goes to ground thru R42 (680 ohms).
The control voltage being too high could be due to: R44 being too low in value, or R42 being too high in value. Those would be the first things I would check. Then disconnect one end of the pot, and connect an ohmmeter to that end and to the wiper. Rotate the control, looking for dead spots. Also be sure the control element (10K) is not open.
Then go ahead and check R40, R41, and R43 (whose purpose appears to be to make the control's action more linear).
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