just received a 488 mkii that is acting up. all channels work fine, but channel 7 plays back material at an incredibly low volume. it WILL record, and it sounds great through the mixer portion of the unit, but upon playback it is -15 to -20 db lower in volume than recorded, and muffled. Using a Maxell XL ii. I also tested a Cassette inside this machine that had recorded material already printed on it from an identical 488, and from track 7 still played back with the pre mentioned symptoms yes i have cleaned the heads with isopropyl alcohol. any ideas? any repair shops on the east coast that can help?