Now that I have my manual and know that
the Model 80 DOES require head calibration/alignment, I can safely tell you that if your playback levels are lower than they should be, the playback head probably needs alignment.
This can be done with the right MRL tape (tape with various sine wave test tones). All you have to do is playback the tape just like you would any tape. While it plays back, you have to look at your playback meters. For each channel, like you said, there are playback alignment adjustment pots located under a panel on the back of the machine. It's just a matter of turning those nobs until you see your tone playback level hit 0db on your meters. Make sure you adjust the correct knobs; some of the knobs are for very technical stuff that would only screw the machine up if you are not a technician.
Record head alignment is done in a similar fashion, although you must send particular tones from an external device (at -10db) and record these tones on a blank tape; when you play them back, if they don't hit zero db, then you have to adjust them like you would the playback knobs.
Of course, this is just a very general explanation. It's all in the manual, though, so I'm sure you won't have any problems. Having tape heads out of alignment can make your deck sound like crap. I bet a lot of people probably thought that their machine was broken or something. And, I bet if those same people went to get their deck repaired, the repair shop probably lied and agreed that it was broken and charged hundreds of dollars to "fix" the deck when it only needed to be aligned, which takes about 10 minutes. Choose your repair personel wisely, in my experience I have found that most of them are very shady people who will rip you off every chance they get. Having a pro tape machine without a manual is a very frustrating problem. I feel so much better now that i have the operations and technical manual.
The hardest part, probably, is finding the right MRL tape. The model 80 requires an MRL-21J103 playback alignment tape, manufactured by Magnetic Reference Labs. It can also use a Fostex Model 9100A Tape or a BASF 45513/2 Calibration Tape , but both these are no longer made and are very hard to come by, used or new. MRL still produces the required tape, but they charge $90 for it! If you think thats bad, for 2", 24 trk machines, they charge around $700 for the required tape. You can safely say they have a monopoly on their hands.