DA-88 Maintenance, Upgrades and Tweaks

For any product, environment can affect the MTBF (Mean Time Before Failure). This is especially true for tape machines, where air quality can contribute
Author:
Publish date:

For any product, environment can affect the MTBF (Mean TimeBefore Failure). This is especially true for tapemachines, where air quality can contribute to MTBF as much as thetype of use or abuse. The Tascam DA-88, for example, has a fan thatdraws air through the tape slot, among other spaces, potentiallyaccelerating mechanical component degradation when the air qualityis in the negative.

Note how the following three environmental examples can affectthe MTBF: a post house that relies heavily on tape is likely tohave the machine turned on 24/7, a power user; workstation usersmay need access to tape but mostly work “offline,”constituting intermediate use; weekend warriors — who alwayswish they had more time — would be classified as inconsistentusers, hot and heavy some weekends, possibly dormant for manyweeks.

In each of these cases, understanding the environment can helppredict, prevent or minimize downtime during periods of criticalneed. If the post house's DA-88 was installed in a proper videomachine room — where air quality control is an art —then it could be “on” 24/7, yet stay relatively cleanand likely go for longer intervals before requiring major service.In a more typical control room environment, turning a“stock” machine off when not in use will minimize thecollection of accumulated dust. High humidity will shorten the MTBFof any videotape-based, helical scan recorder. This is especiallytrue for the earliest DA-88 version — now eight years old— because its nonanodized reel table clutches have beenredesigned three times since and are now stable (for a wear-itempart).

Note: The information in this column could be dangerous in thewrong hands. Trying to help two diverse groups — users andtechnicians — could potentially compromise the material. Alltape machines should get a routine inspection every 250 to 500hours, especially if you aren't the type to pop the hood and atleast take a look-see. Also, establish a relationship with aservice company: There's a reasonable chance life can be extendedand maintenance costs reduced via scheduled maintenance.

NICE HEAD

Like a used car, tape machine usage is judged by head hours, notjust the “on” hours. Yet being “on” and ina negative environment, for a stock DA-88, invites foreign matterinto the transport area. No counter keeps track of that. The fanreversal and filter modification detailed atwww.tangible-technology.com is very effective at trapping airbornecontaminants before they can muck up to the transport. There areplenty of digital tape machine tips on my Website. Your feedback iswelcome.

In light of California's power deregulation mistake —don't get me started — I wouldn't suggest that you counteracthigh humidity by leaving the machine on (even with the addedfilter). Note that DA-88s were shipped with a silica gel pack. Forhumid environs, mount the machine in its own rackcase with thesilica gel pack tucked inside. Put the front and rear covers onwhen not in use. With luck, the heat generated when the machine ison will “reset” the pack for the next storage period.If not, then the food dehydrator specified on my analog taperestoration page is a good choice.

TENSION IN THE CASSETTE SHELL

Since the dawn of the ADAT, it is often recommended (and Iconcur) that users fast-wind new tapes before recording orformatting — primarily to redistribute the tape pack. Newtapes may have higher tension than rewound tapes, so this is onesource of potential wear or instability during that first importantrecording. Depending on whether the tape is wound in the shell orthrough the transport, some shedding may occur, but contrary tomyth, tapes that are shed-prone don't just “fix”themselves. Loose bits of oxide have to go somewhere.

After the earliest DA-88s rolled off the assembly line, a“self-cleaning” mechanism was added, and a retrofit kitis still available. (The part and not the labor, which is minimal,is covered under warranty.) The kit comes in two pieces; the mostessential being a sharp Ruby “scraper” that removessurface oxide before it can contaminate the heads. Keep in mindthat tape edges also contribute to the shed factor and are notaddressed by the scraper.

Look at the bottom of the stationary guide just to the left ofthe capstan shaft. If you see black, then the “rabbet,”the bottom ledge along the circumference of the head drum, is alsolikely to be contaminated. Figure 1a zooms in on a DA-88 headassembly — the rabbet is the ledge around the circumferenceof the head drum. Figure 1b shows how a clogged rabbet affects RFoutput, especially at the left side of the head where the tapeenters. This condition, which can happen to any DTRS model, willcompromise the machine's ability to read timecode, as well astracks 1 and 2. Cleaning the rabbet is a technician's job. Don'ttry this at home, kids.

EC'S OBSESSION

I have two obsessions regarding all tape recorders: Themechanism should be gentle to the tape, and the tape, via tensiontweaks, should be gentle to the heads.

The most significant issue for a digital tape recorder is theefficiency that data can be exchanged with the tape. When all partsare new, there is a significant amount of “dataheadroom.” A new head needs less tension than an“old” head. As parts wear, this headroom is diminisheduntil the errors can no longer be concealed. The best preventivemaintenance will be repeated ad nauseum here: Check the error rateand learn how to manually clean the heads.

Head life is most significantly affected by tension, not just inplay, but in reverse play, when the former supply reel temporarilybecomes a take-up reel. It is easy to overlook this measurement,and when the supply reel clutch is defective, the tension acrossthe heads in Reverse Play mode can be double the specifiedrange.

“BACK” TENSION?

This term describes the supply reel tension applied to the headassembly when in Play mode. On all DTRS transports, back tension isadjustable via black coiled spring as detailed in the Januaryedition of “The Tech's Files” (as a picture) and thismonth as a drawing. But it's not as simple as that, because thereis also a tension arm position adjustment, and the two“tweaks” interact with each other.

Figure 2, from the DTRS manual, indicates the optimum positionof the tension arm. This is one adjustment that I feel could bemore precisely detailed. I start with the tension spring set tominimum, playing a fully rewound 113-minute tape to set the tensionarm position. Only afterward should the tension be measured. The“spec” is 10 to 12 gram-centimeters (g-cm); it is often14 to 16 g-cm on older machines, and, in my opinion, 10 g-cm shouldbe the maximum value.

The point of optimizing the tension arm position is so that themachine will not be fussy at the head of longer tapes. The additionof the self-cleaning mechanism narrowed the usable range of theadjustment.

DA-88 UPGRADE LIST

You might be surprised at how many DA-88s still have theiroriginal heads. This is not a comment on the machine's geneticdisposition, just an indication that some older, low-mileagemachines come in for service needing many of the factory upgrades.I still get them. DA-88s before serial number 100000 were madearound 1993-ish, while serial number 320000, for example, is circa1995. The fifth- and sixth-place digits are lot numbers. In theseexamples, lot 10 and lot 32, respectively. If you own or encounterone of the older, low-mileage decks, then it should be overhauledsooner rather than later.

Here's a partial list of DA-88 updates (with an error message inparenthesis when applicable).

  1. self-cleaning kit: This two-part kit consists of a sharp Ruby“scraper” that is highly effective at removing loosedebris from the tape before it gets on the heads. A second ratherannoying sub-assembly periodically dabs the heads in an attempt toclean them.
  2. slide cam: This simple piece of plastic engages the brakes andtightens the clutches. The difference between old and new parts isa smoother transition to a notch that sets up the Fast Windmode.
  3. slide cam lever/actuator: (S-err-31/41) There are three possibleFast Wind failure modes: bad solenoid, bad solenoid circuit (coldsolder joints) and a damaged lever arm, the latter caused by afracture at the bend in the metal work. The crack is hard to see,even when you know it is there. See Fig. 3.
  4. reel tables: Redesigned three times, and one of the primaryannoyances is the interaction of the black optical encoder discwith the lower portion of the reel table clutch. Over time, theblack shaft compresses and creates friction. The new reel tabledesign seems to have solved this problem.
  5. cam and sector gear: (S-err-11) A limited run of DA-88s —with serial numbers between (approximately) 240000 and 360000— suffer from this “stuck loading guide” errormessage. Under-spec pin length causes damage to a plastic cam.
  6. back tension coil spring: When replacing the back tension felt,a “silver” coil spring on the underside of the assemblyensures positive contact with the tension lever position adjustmentmentioned above and detailed in Fig. 2. This spring was modifiedboth to facilitate reassembly and to ensure positiveengagement.
  7. back-up battery: The three VDC lithium backup batteries shouldbe periodically checked to make certain it measures 2.6 volts orhigher. Even more important, inspect for leakage before circuitboard damage is beyond repair. I use a different battery thanrecommended, because its vapor seal minimizes “batteryexhaust” that can eat copper circuit traces.
  8. slant blocks: The slant block is the lower portion of theloading guides. When there isn't a tape in the machine, they areloose to the point of seeming to be broken. This is normal. Theybecome “precise” once fully extended and pressure fitagainst the “V” guides. Slant blocks are perhaps themost mysterious parts in all digital audio recorders, because theyare difficult to measure and there are no adjustments except forguide height. There should be a front-to-back tilt adjustment tominimize curling, especially in the exit guide.
  9. lubricant: For all helical tape transports — DAT, ADAT andDTRS — any lubricant applied to the loading guide pathsshould be wiped clean, leaving only a molecular layer. Tape thataccidentally becomes slack and makes contact with the lube willbecome very attractive to a head spinning at 2,000 rpm!

Happy Motoring! Next month: under the hood of a TascamDA-78HR.

For more information about maintaining your gear in topshape, visit Eddie Ciletti's Website at www.tangible-technology.com.