There are many opinions about head cleaning. These are the facts:
Hello, experienced tech here, with a pair of pictures and points on manual head cleaning. The common tools are 99% (low moisture/anhydrous) Isopropyl alcohol and a lint-free cloth. Both are available at your local audio support center. Moisten the cloth with alcohol, place it against the head and this part is highly recommended rotate the head in the counter-clockwise direction. Some heads are more forgiving than others, but on a DA-38 / -88 / -98, rotation is critical absolutely counter-clockwise only because the head surface is asymmetrical, one edge being particularly sharp. Remember, a head change due to carelessness will cost you about $750!
This page specifically deals with Tascams "DTRS" format (the DA-38 / -88 / -98) and the Alesis Adat. However, the "views" on this page apply to any helically scanned machine, including DAT. A DAT mechanism is so small that you may want to browse here if only for the luxury of size. The adat, for example, is large enough to make some of the more obscure components more obvious. For "DAT-centric" information, click here. For Panasonic's SV-3200 / -3700 / -3900 / -4100, Pick Me!
Lots of people use chamois (shammy) sticks to clean their helical tape heads. For some DAT machines, this is the only practical way to gain access without removing the loading mechanism. Serious head cleaning, however, starts with the removal of such "obstacles" because (believe it or not) it can sometimes take ten minutes or so to dissolve and remove all of the dirt. I prefer Twillwipes by Chemtronics (call 800-645-5244 for a distributor near you). These come in six-inch square sheets that I cut into one-inch by two-inch squares.
Environmentally-friendly 99% alcohol is a slow evaporator, so you must allow for additional drying time before rolling tape, otherwise, the tape may get wrapped around the heads. I found that using a second cloth to dry the heads removed more dirt than just the damp cloth. Figure Three shows a cloth after several swipes. Alternate between damp and dry cloths until no dirt is collected.
Figure 3: Proof that the dry cloth picks up more funk
The "RABBET" is a mechanical ledge on which the lower edge of tape travels as it passes around the rotary head assembly. (See Figure 4 below.) Cleaning tapes can't remove the oxide that collects on this "bunny." Do not attempt to clean the Rabbet unless you can confirm, with an oscilloscope, that it does indeed need cleaning. Figure 5 shows the RF envelope that results from a clogged Rabbet. If you feel bold enough to clean the Rabbet, position the drum so that the heads are no where near the work area. There are either two or four little black specks embedded in the drum -- these are the heads that actually get signal to and from the tape.
To clean the Rabbet, use a shaved tooth pick or bamboo skewer soaked in alcohol. Lay the stick on the Rabbet and follow it around the entire circumference of the tape's path. Trim the stick with a razor blade after each swipe. The only way to have enough room to safely do this on a DA-88 is to remove the transport from the chassis, the loading mechanism from the transport as well as the "mode" motor. DO NOT GO ANYWHERE NEAR THE HEADS WITH THE STICK!!!
The envelope above has four arrows that point to places in the RF envelope where dirt on the Rabbet pinches the tape and reduces signal output.
Signs that the heads are dirty or worn, or that the Rabbet is clogged:
There are plenty of other obstacles, not the least of which is the tape itself. I can not overemphasize the importanct of changing tape type, brand etc. in an attempt to isolate a problem. Too often I have repaired a machine -- obviously in need -- only to have a customer not be fully satisfied. Changing the tape often does the trick.
Other obstacles to great performance are the clutches that regulate take-up tension. (Dedicated reel motors would solve this problem.) A stock DA-88, for example, sucks air through the "tape insertion port." Airborne contaminants are particularly irritating to the reel tables, each of which has a magnetic clutch to regulate tension. Figure Six details the assembly which, (normally) from top to bottom, consists of the reel table and magnet (the former makes mechanical contact with the tape hubs in the cassette), a spacer (this sets the amount of tension), the "magnetically attractive" base (older versions were not anodized and may rust in humid environs) and an optical reflector (for generating motion signals).
Figure Six: DA-38 / DA-88 / DA-98 Reel Table Assembly
This part was redesigned three times. Newest version not shown.
Even though the capstan motor is responsible for precise control of
tape speed, dirt in the clutches can make the tension both irregular and
higher than normal. This mechanical interference will increase the
error rate as well as generate mechanical error messages. The long
term solution is to reverse the fans direction,
add an external air filter, have the mechanism thoroughly cleaned, replace
the reel tables (if necessary) and regularly monitor error rate.
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