Martin,
The high brightness is likely bad d-c restorer diodes being leaky. Replace them with 1N4937. Also replace the 22meg 1/4W carbon resistor near that circuit with a Vishay VR37. This is a 1/2W 1% type. The original is highly likely high in resistance. When this resistor is high in value, the trace will be bright then dim as it warms up over 10-20 minutes without touching the intensity control.
The 15V regulated supply at 22V is likely a shorted series pass transistor, Q701. It could be a bad IC, U712B. also replace the zener, VR725 with a BZX85B9V1 (this type is VERY likely open) and change R726 to a 6200ohm 1% 2W type (about 16mm or larger length). The original resistor is 1/2W and likely burned, brown body, and out of tolerance. I have seen this resistor in this circuit bad enough times to change it on sight. Mouser has the parts, except for the 6200 ohm 2W resistor. That is available on ebay.
Mark
