DOA is a possible cause of the trouble. The following is posted @ Solid Signal:
INVENTORY STATUS UPDATE FOR
ANTENNA ROTATORS AND PRE-AMPLIFIERS BY CHANNEL MASTER
In response to several inquiries regarding the delivery status of our antenna rotators and pre-amplifiers, we are sorry to inform you deliveries from our factory are delayed and we are unable to ship the finished goods based on our original promise dates. The delay is a result of difficulties obtaining the necessary raw materials used in manufacturing these products due to tighter restrictions on sub-components necessary for maintaining an acceptable level of quality.
Our apologies for the inconvenience this is causing you and your customers. We are doing everything we can to expedite finished products from our factory once the raw materials are received. We will forward updates to you as they are relayed to us from the factory. Your patience is appreciated during this time.
Sincerely,
Joe
Joe Bingochea
VP of Product Management & Marketing Channel Master
The voltage rating of most consumer equipment 'wall-wart' and 'brick-style' power supplies is based on full-load conditions. 22.5 volts with no-load sounds typical for a 15 volt supply.
In addition to TV signals, the amplifier can also be overloaded by FM and other radio signals. The CM7777 has a switchable FM trap. If you have not already, verify it's 'IN'.
I agree, a low noise, high input amplifier would have been my recommendation. Consider the Antennas Direct CPA-19 and Winegard HDP-269.