Have fun! The first thing I inspect is the tape path including the heads. Clean all these parts throughly before the inspection process. Look closely at the guides (near the heads). Look for flat spots from tape wear as it is a good indicator of how much the machine has been used. Flat spots on the guides isnt necessarily a deal breaker, but raises a caution flag for me. Most pro-sumer machines have the ability to rotate the guides to a "fresh spot". Next the tape lifters (again next to the heads), looking for flat spots indicating high usage. The problem here is that most of this level of machine those lifters are not rotatable. Then the heads themselves. Visual inspection of heads will only take you so far. I look for a uniform polished appearance to the entire face of each of the heads. There will more than likely be a wear pattern. It should be uniform in width from top to bottom. Narrower is generally better. The wear pattern should also be centered (left to right) on the gaps in the heads. Using a magnifying glass look at the face of each head, especially the gap. They should be minute and uniform from track to track. If one (or more) appears wider it is an indication of the heads being at the end of their service live. They also cannot be refurbished once they are that worn. Heads are pretty much the determining factor for me when I make a decision on a deck. They can be very expensive to replace, especially as track count goes up. Many times it just doesnt make sense to fool with a multitrack that needs heads because of how high it drives the investment. Next the pinch roller. The rubber can either harden over time or start to decompose. The good news is that the roller is easily replaced with a new one (if available) or can be sent out to be "retreaded" for lack of a better term. Im not up on Tascam 48s but I think that is a three motor machine so you dont have to worry about deteriorated drive belts, rollers and other nonsense located in the bowels.
Next its time to do some operation checks. Switch on. Quiet? Check indicator and VU lights for operation. Load a known good tape onto the machine and put it through its paces for fast forward and rewind. Check for smoothness and how well the machine is packing tape onto the reels. Listen for tape scraping the edge of the reels. This isnt necessarily a big deal, just needs some alignment attention. Again, not knowing the 48 I dont know if it has a built in oscillator. If it does record some test tones, then play them back. Check levels for an indication of record and playback operation. Listen too for any warbling in the tones during playback.
That is usually enough for me to make decision on buying or walking.
Hope this helps some.
