Servicing a SONY DAT machine (Pictorial)

Discussion in 'Tape' started by SaSi, Sep 17, 2008.

  1. SaSi

    SaSi Seriously Illogical Subscriber

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    As discussed in a previous thread, I now have two Sony DAT decks that need repair. One DTC 59ES that loads tape but doesn't move it in any fashion and a DTC670 that doesn't even load the tape.

    Although I suspect what is wrong with both machines, I haven't yet repaired them or know what exactly the problem is. It will all unfold as I disassemble them, along with pictures and discussion.

    I will - hopefully - be able to repair the 59ES as it appears to show the "sluggish" FF/REW syndrome, only so much pronounced that not even PLAY engages properly. The 670 seems an easy repair of a different nature.

    As the pictures will show, despite the differences, the transport mechanisms are identical. In fact, I've seen only two different transports so far:

    * DTC55ES has what appears to be the oldest (and best IMHO) transport with 3 motors and lots of metal parts.

    *DTC 57, 59, 670, 690, Z700 all share the same transport block with the 57 lacking a sensor block and thus having a narrower ribbon cable. But parts are totaly exchangeable.

    I also have a PCM R500 that has 4 motors and works like a charm, so I haven't opened it up (yet). I bet this one has a different transport block as well.

    The only differences between all the above decks are the loading mechanism. It is nice to see how Sony realized their mistakes in the earlier models and improved upon them with every new model. So if you have any of the above decks with a mechanical glitch, read on.

    So, enough talking, let's start the stripping...
     

     

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  2. SaSi

    SaSi Seriously Illogical Subscriber

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    Preparing the unit

    Before we are able to reach the transport mechanism, we need to remove the cover.

    A word of caution. Unplug the unit from power. Use a bench of adequate size and plenty of light. Don't rush things. If you haven't done this before, don't start now. Disassembly and re-assembly require no power to the unit and it is prefferable that way. Some of the testing require power and unless you totally assemble it for testing, it can be dangerous if you don't know how to work with an audio device. You have been warned!

    Before you start, power up the unit, press eject and remove the cassette compartment cover by gently pulling it upward. Then shuttoff the unit and unplug it. If the deck is not responsive or a cassette is jammed inside, don't worry, this can be done manually after opening the unit.

    Typically, there are 2 screws to each side for a total of 4. Some decks also have another screw in the back securing the top cover to the back panel. Some others (like the DTC 59ES) have another 4 screws on the top.

    These need to be unfastened using a Philips screwdriver. If you are using bits, the PH1 is the best size.

    After all this, the unit looks like the one in the attached picture.
     

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  3. Strawman

    Strawman Moderator

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    Looks like an interesting thread. Please heed Sasi's warning about electrical power if you attempt anything similar.
     
  4. SaSi

    SaSi Seriously Illogical Subscriber

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    The Head cleaner - A tale of sorrow

    The attached picture is a sidetrack to the discussion.

    It shows a close-up of the drum with the foam wheel the designer thought would clean the head. When the tape isn't loaded against the drum, this foam wheel touches the head as the spin stops. It acts as a break and supposedly cleans the drum - if we believe the Sony designation for the part. The foam part is attached to a white lever that moves towards the drum forced by a small spring underneath. When the tape is loaded, the right hand side tape guide (called T1) pushes the lever away from the drum. In some decks I've seen the T1 obscured by the lever and fails to travel to the stop thus loading the tape badly. This results in bad tracking or even tape jamming.

    I see this foam part mostly disintegrated. The one shown in the picture is in pristine condition but once we start working with the deck it might break up. We shall see.

    It is worthwhile to note that in later models that thing was replaced with a plastic blade that perhaps does a better job but certainly doesn't break up.

    I choose to remove that foam and it's assosiated plastic arm. Makes no sense and it probably contaminates the drum rather than cleaning it. If your deck needs cleaning often, it is perhaps because of this.
     

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  5. SaSi

    SaSi Seriously Illogical Subscriber

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    The cassette loading mechanism

    The transport is encased in the cassette loading mechanism. This mechanism is secured in the deck by 3 or 4 screws, depending on the model.
    Earlier (less evolved :D) models used a metal casing for the transport and 3 or 4 screws.
    Later models switched to plastic casing (cassette loading mechanism) and 4 screws.
    The attached pictures show the 4 screws of this particular model with red arrows. The first picture shows the complete foam wheel and white lever as well.

    The cassette loading mechanism is the only major difference between various decks and some discussions on this as we proceed will be relevant to this model only. However, the DTC690 uses exactly the same thing and the DTC -ZE700 a very similar one.

    We will discuss small differences with the DTC 670.
     

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  6. SaSi

    SaSi Seriously Illogical Subscriber

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    Connections to the main PCB

    The transport assembly is connected to the main PCB by means of 4 cables.

    These are shown connected to the PCB in the first picture and also shown numbered in the second picture.

    As numbered,
    1. The white flat ribbon cable is attached by pressure to the ribbon socket. It transfers control signals, auxiliary motor signals and sensor signals.

    2. The small red plug is the capstan motor control.

    3. The small white plug isn't actually part of the transport mechanism, but connects to the cassette loading motor directly.

    4. The large white socket with lots of shielded cables connects to the drum head. It transfers signal and motor control.

    Cables 2, 3 & 4 are braced togther with a plastic clip (barely showing in the top of pic 36650 - sorry for that...). Twist and release it and keep it safe. It's better to clip these cables together when finished for a better look.

    Remove the cables from their sockets and unfasten the 4 screws. It's easier to use a magnetic screwdriver so the screws don't fall inside the deck.

    When the 4 screws are removed, we can pull the transport out of the deck. This is much easier with the cassette loader in the eject position. If the cassette loader was retracted before that, rotate the large white flywheel to the left of the transport until the mechanism is "ejected".

    If there was a tape inside the deck, jammed, causing the mechanism to "refuse" unloading the tape, if you don't really care about the tape, follow the same procedure until the tape is ejected with tape still loaded around the drum or jammed inside the transport. Depending on how the tape is jammed you can gently pull the cassette out and later respool the tape inside the cassette with a thin pencil or screwdriver turning the spools. If you care about the tape, wait until I show you the DTC670 - It has a tape jammed inside.

    When finished we can put the deck aside and keep the transport assembly on the bench. It looks like the one in the third picture.
     

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  7. SaSi

    SaSi Seriously Illogical Subscriber

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    Cassette loading mechanism - further disassembly

    Before we break apart the transport from the cassette loading mechanism, we need to remove one piece from them. If we don't remove it willingly it will come off by itself as we disassemble the block. This is bad as you won't be able to see how it is mounted and how to put it back together.

    The part in question is the spring loaded front cover holder. It is mounted at the two edges of the loader assembly (red arrows on the 3rd pic) and spring loaded with a spring so that the cover closes as the cassette is loaded.

    Gently pull the spring end that is attached to the front cover and release it from that position. The spring will unload and remain in it's socket.

    The cover holder can then be removed by gently pulling the two ends of the loader assembly apart. If you feel uneasy, leave it there and watch how it is released once the screws are unfastened.
     

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  8. SaSi

    SaSi Seriously Illogical Subscriber

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    Separation of the transport from the cassette loader

    There are 4 screws that attach the transport inside the cassette loader. These are shown with arrows in the pics.

    There are two screws to the left and another two to the right. The right hand side is easy - the screws are very obvious.

    The left hand side is tricky.

    The rear screw is only visible and reachable when the cassette holder is fully extended in the eject position. You can do that by manually rotating the large white wheel.

    The front screw is visible and accessible on this mechanism - although the pic shows it from an angle.

    You will notice that the large flywheel has 3 holes at 120 degree angles. Some models have a larger flywheel that has 6 such holes. In such models the front screw is only accessible through the outer set of holes using a screwdriver through the hole.

    In this particular model the screwdriver reaches the screw directly.

    I feel inclined to point out that the DTC55 has a large flywheel and no holes! When I was taking it apart I felt lost there as I couldn't reach the screw. I should have totaly disassembled the flywheel and cogs it drives and remove the flywheel to reach that screw.

    I decided to "retrofit" the improvement in the mechanism that Sony engineers did in the later models and drill a small hole on the flywheel so I could reach the screw. Saved me a lot of pointless effort. You might find this is destroying the deck, but I fear that unnecessary disassembly is worse.

    You can unfasten the screws with the transport block either to each side or in the normal orientation shown in the pictures. Choose what seems easier to you.
     

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  9. SaSi

    SaSi Seriously Illogical Subscriber

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    The separation!

    In the next few pictures we can see the steps towards the separation as well as the removal of the spring loaded front cover.

    The final picture shows the 4 screws that are unique to this assembly. Put these together with the 3-4 screws securing the whole block to the deck and the screws holding the top cover.

    The 3rd picture shows the transport separated from the loader. An interesting piece of information can be retrieved there. All DAT transports I've seen so far have a date printed on them. This particular one is dated December 26th, 1992.

    If your cassette loader assembly doesn't look like the one in the picture any more and has broken apart in two pieces, read the next post.
     

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  10. SaSi

    SaSi Seriously Illogical Subscriber

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    The cassette loader can be split apart in two pieces.

    The cassette loader is designed so that it comprises of three main segments.

    The left part with the motor and pulley,

    The middle part, that actually holds the cassette

    The right side part that is simply a piece of plastic.

    No further disassembly is required here, but the right side part can be split if the right panel is rotated. The picture (tries to) show that the right panel is mounted to the central segment using a rod and a safety clip that once rotated allows the two parts to split. If that happens by accident, remount them as shown.
     

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  11. SaSi

    SaSi Seriously Illogical Subscriber

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    A break for today

    This is as far as I've reached with this deck today. Taking pictures, processing them and writing this up really takes more time than the actual operation. If you are even slightly experienced with cassette and R2R deck servicing, this is easy. The only hard part is some tools that - obviously - are smaller than what is needed for R2R plus a tool that needs to be custom made.

    As it is getting late here (2:00am) I will continue tomorrow with a close up inspection of the transport, some things that can be checked before disassembly and an explanation of the various parts and problems that can be fixed without further disassembly.

    Feel free to post questions or comments - I would like this to be interactive - if you have. I am hoping that as we reach the heart of the problem experienced troubleshooters might give some suggestions as to what is causing the sluggish spool performance this particular deck (and a few others) have.
     
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  12. SaSi

    SaSi Seriously Illogical Subscriber

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    A guided tour of the transport

    For the next step we need to get better aquainted with the transport mechanism. The attached picture shows the transport from the top.

    The two needle micro-sensors shown numbered 1 are for cassette in and rec. inhibit sensing. They travel to the small PCB to the right and from there to the drum control PCB in the back of the transport. Along the way two more sensors are located under that PCB to sense the home position for the bridge that expands the tape load arms (numbered 2 and 3) and the pinch roller (4).

    The empty circle in the bottom left corner shows ... nothing. Older transports don't have anything there, just a hole where an extra PCB is mounted in newer models that accomodates an extra set of three pin sensors for media recognition.

    How this hole exists before it was decided to mount something there, escapes me. :scratch2: Sony probably knew they had to put something there but left it for later models - perhaps.

    The two arms that expand (2 and 3) follow the curved track and end at the two steel stops. Each arm has a pulley and a front "tooth" that needs to go under the stop gap at the end of the travel so that the pulleys are securely in place.

    One of the faults in some transports is that one or both of these teeth don't go under the stop. I am guessing this happens when a tape is mangled and is pulled with force. As the cassette reels are secured with clamps when the cassette is ejected, the tape acts as a sling and may pull these fragile levers and bend what is underneath.

    This fault can be diagnosed before dismantling . There are other faults that can be diagnosed and fixed without dismantling, but they will be covered after the stripping description as it is easier to understand everything when the whole of the transport is explained.

    The two tape loading arms are named S1 for the left hand side one and T1 for the right hand side one. I will refer to them as such further on.

    The pinch roller is small as you see and secured in place by means of a plastic circular clip. One of the faults DATs develop is a slippery roller. I have found that the normal rubber rejuvenator for open reel rollers is too strong for them. I have had terrific results by rubbing the roller with a cotton pad dampened with alcohol.
     

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  13. SaSi

    SaSi Seriously Illogical Subscriber

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    S1 & T1 tape load pulleys

    The two tension and load arms and pulleys are the reason why many DAT recorders fail to correctly playback either DAT tapes from others or tapes recorded on the same recorder years ago.

    These are adjustable and by adjusting them we ensure correct tracking in almost the same fashion we need to adjust head azimuth on cassette decks and R2R decks.

    The attached pictures show the tension arm securely fit at the travel stop, the adjustment slot on the top (with a protrusion in the center that doesn't allow a normal flat screwdriver to be used for adjustments) and the two black screws that secure the stop on the transport plate.

    I have seen one case where the black screws were not tightly done and the arm wasn't secure in it's resting place. This resulted in random mis tracking during playback.

    The two adjustment pulleys can be rotated and the screw they are mounted upon lifts or drops them, thus altering the azimuth.

    Don't touch them for now and don't worry that dismantling will ruin the alignment. The alignment is ensured by the fact that the tooth in the front of the arm locks inside the stop.
     

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  14. SaSi

    SaSi Seriously Illogical Subscriber

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    Backtensiopn adjustment

    To the left edge of the transport (as seen in the picture) there is a small cross screw. This screw controls back tension. When fully in, back tension is at it's max. When out, back tension is at it's minimum.

    Forward tension / torgue is adjusted electrically (will talk about it during adjustments).

    Make sure the screw is there.
     

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  15. SaSi

    SaSi Seriously Illogical Subscriber

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    Tape load extension mechanism

    At the front right edge of the transport you can see a set of gears, white and black. From the front you can touch the black one.

    These gears move the bridge inside the transport from left to right which extends and retracts S1 & T1. It also moves the pinch roller in contact with the capstan.

    You should be able to rotate the black gear with a single finger and see the arms slowly extend and retract as you rotate the gear in oposite directions.

    If you feel there is too much friction and you cannot easily rotate the gear, it means there is something wrong in there. It can be either dirt, or someone lubricated the transport with the wrong material, or one of the arms is bent, or someone tried to fix the transport and left stray cables that inhibt the arms from moving.

    When the arms are fully extended, rotate the black gear some more. It should start to move the pinch roller further until it contacts the capstan. When this happens, check to see that the pinch roller is really in contact with the pinch roller and that it doesn't slip. Try to rotate the roller and if it does then it is either not in contact or is slippery. Check visually for contact.
     

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  16. nakmandan

    nakmandan Vintage Nak enthusiast

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    Excellent work SaSi! Very detailed pictures. I look forward to reading more as you post.

    I have been lucky so far in that my DTC-75ES has always and continues to work well, even after 17 years. Never had it serviced or opened. I'm the only owner it's ever had, got it direct from a Sony employee. I know my luck can't continue for much longer however, that's why I'm so interested in this thread. I don't recall ever seeing a comprehensive DAT maintenance thread anywhere else. A true trailblazer you are my friend!

    The only problem I've ever had with my machine is that 3 or 4 (out of more than 100) tapes I made 16-17 years ago have a few digital dropouts in them. Not sure if it's the tape or the machine starting to go out of alignment. I suspect it's the tape because all of my other tapes, even a few recorded on a different machine (an A&D D-930), continue to play well.
     

     

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  17. niklasthedol

    niklasthedol Super Member

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    Very Cool thread SaSi.

    I'm not into DAT renovating myself and not realy much into DAT at all.

    But the way you contribute is great.

    "dolph"
     
  18. rockin1150

    rockin1150 Super Member

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    Nice! I always wanted to see how those machines looked inside:thmbsp:
     
  19. SaSi

    SaSi Seriously Illogical Subscriber

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    Spoolint mechanism

    In the bottom of transport the only thing visible is the spooling motor and the spooling gear connected with a geared belt.

    This belt needs to be hard and loose. In some models, the second screw mounting the spooling motor is adjustable. Don't be tempted to adjust so that the belt is fastened. Nothing will work then. The belt needs to be loose, just enough so that it doesn't disengage from the gear.

    The idea behind this will become obvious as the transport is opened up.

    Before doing that, one test that needs to be done is to manualy rotate the spooling gear clockwise and counter clockwise (parts of a rotation are enough).

    One direction should give a small rotation on the left spool and the oposite direction should give a small rotation on the right spool.

    On the transport at hand, the take up reel doesn't rotate but the left one does. That explains why tape can be loaded and safely unloaded but not played or FF/REW. We are getting closer to facing the problem.
     

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  20. SaSi

    SaSi Seriously Illogical Subscriber

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    Thanks guys. I stopped todays session for a quick nap and saw the postings after I continued. It was getting a little lonely in here...

    @Nakmandan, the DAT tapes are very very sensitive to curling and bents. Even the slightest bending will cause audible distortion sounding like a dropout or digital noise. It is because the tape at the bend or fold looses contact with the head and when it passes through the S1 T1 guides it changes azimuth.

    In all fairness, I knew nothing about DAT some 4 months or so ago. You can look up a question I posted about tapes not reproduced properly on one machine and good on another. I confess I wasn't convinced by the answers so I just had to dig more.
     

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