Servicing a SONY DAT machine (Pictorial)

An observation

The attached picture shows an anomaly on the back side PCB. This red color shouldn't be there. It's not my blood or something. I have no idea what it is or if it affects anything.

I am spotting this as during troubleshooting one needs to be alert for minor things that act as telltales for problems.

On another deck all the screws were loose. What does this suggest? That someone had worked on the unit, forcing me to look out for iregularities, misplaced parts or badly repaired faults causing other problems.
 

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Dismantling

The transport consists of three main blocks. The top transport plate that is visible when looking at the drum head, the bottom transport mechanism that is screwed on the plate from below and the drum control board that is fastened atop that.

We work from the back so we need to rest the mechanism face down (or better drum down). If you are afraid to rest the drum on the bench I feel for you, I've had the same feeling myself when doing it for the first time.

As long as excessive force isn't applied all is ok. Just make sure the work surface is clean of dust, metal particles and liquids. No coffee allowed here.

We start by removing the drum control plate. On this particular model it is easier than newer ones as the left hand side media detect sensors are missing and so is the extra cable that comes with them. You will have a chance to see how this complicates things with the 670 that follows.

The short story is we need to undo the 3 screws, one at the center of the PCB and two more fastening it in the back directly on the metal chasis of the transport. We have two different types of screws here.

Once the screws are removed, we need to slide the PCB backwards so that the 4 cables traversing the board don't get in the way, raise those cables and bring them under the PCB and while raising the PCB for the first time since Sony assembled it, untie the cables inside from the two metal guards.

Sounds complicated but take a look at the pictures and it will become clear.

Picture 1 shows the PCB in place but screws removed.
Picture 2 shows the PCB slightly shifted to the back and the cables disengaged from it.
Picture 3 shows a peek of the cables underneath as they are settled.
Picture 4 shows the PCB laid aside leaving ample access to the transport mechanism itself.
 

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The attached picture shows an anomaly on the back side PCB. This red color shouldn't be there. It's not my blood or something. I have no idea what it is or if it affects anything.

I am spotting this as during troubleshooting one needs to be alert for minor things that act as telltales for problems.

On another deck all the screws were loose. What does this suggest? That someone had worked on the unit, forcing me to look out for iregularities, misplaced parts or badly repaired faults causing other problems.
That stuff actually looks like the glue or epoxy whatever used to hold the SMD components in the foreground of the picture. Careless assembly? Does it come off?
 
Closer inspection of the transport from the bottom

Now that the PCB is removed, we can have a closer look at the transport from the bottom.

The spooling motor, belt and spooling gear are now clearly visible. We can test the tightness of the belt and can also repeat the same test as before for the spooling gear. We can see the striped bottoms of the cassette reels turning or not as we rotate the gear. These stripes form a feedback to the magnetic sensors that are mounted on the drum control PCB. They sense if the reels rotate when they should and stop the unit when they sense reels don't move when they should. For this reason it is impossible to test the transport in it's current state - although that would be desirable.

At the left edge of the black plastic area the motor controlling tension arms and pinch roller is seen.

Next to it we have the capstan motor. It's the one with the designation U-17B. It is a miniature of the motor's I've seen on my Revox B710 and ultra miniature of the direct drive motor on the Revox TTs, so you understand this motor gained some respect from me :D. What didn't help gain any respect is the spooling mechanism that is the source of all the troubles.

To the right of the capstan motor we can see the bottom of the drum motor in the shade.

So, ignoring the mechanised cassette loading and the moving drum, we have a 3 motor DAT transport here. So now you know, 3 motor DAT transports are the cheap, low end versions. The better versions are the 4 motor transports that lose the gears and place one motor under each spool.

We have more work to do now to split the transport in two parts. There are 4 screws to undo. They are anotated with arrows in the pictures. 4 black long screws and 1 brass screw securing the underside of the transport at the front edge of the main chasis.

I recommend that you undo the 4 black screws first and leave the brass screw last.

Once all 4 screws are removed we need to gently lift the undercarriage. And by gently I mean slowly and carefully watching for things that might be thrown out. :D OK, this won't happen but there are a couple of spring loaded parts inside and a mishap with a tape might have caused them to jam. In some cases a simple removal of the undercarriage, inspection and reassembly is all that is needed.

When I raised the undercarriage I felt resistance at first - this is why I am giving the advice on going gently. I knew I was not doing something wrong so I continued gently and felt a small snap and the resistance was gone.

I did not see what was jammed but I suspect it has to do with the tension arms as I felt them hard to move by hand and they are spring loaded.
 

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That stuff actually looks like the glue or epoxy whatever used to hold the SMD components in the foreground of the picture. Careless assembly? Does it come off?

Haven't tried. And as I see it all SMD components have a red dot under them... Could this have to do with the fact that the unit was assembled around Christmas?:scratch2:
 
We are Inside!

We are now inside the transport, having visual access to all the parts. Further dismantling is still possible and sometimes required, especially if a part needs replacement.

The attached picture shows everything together: The main transport chasis to the left laying on it's top, the undercarriage to the right and the Drum drive board to the back. On this picture the magnetic motion sensors for the reels are more clearly visible as the white components with the black part in their center.

We now need to take a break in breaking things apart and familiarize ourselves with what we see. And I need to take a break as I take a few more pictures.
 

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The inside of the main transport chasis

The attached pictures show a general overview of the assembly and some close up details of parts of major interest.

We have already seen the capstan before and now we can see it in it's full glory unobscured by other parts. The two screws visible on the capstan motor's PCB are of no interest The capstan motor is mounted on the chasis by means of 3 ultra miniature screws facing the top plate. If we need to remove the capstan motor we need to have a set of jeweler's screwdrivers of high quality.

The lower part of the picture is dominated by the white plastic part, what I call "the bridge". You may come up with a better name - English isn't my native language.

This part has a toothed edge to the left. The set of white and black gears we tried to move by hand before dismantling engage here in a rack and pinion fashion to move the part left and right.

As we see it depicted here the bridge is towards it's right end of travel but not quite so. Therefore we can see the tape tension arms slightly extracted upwards towards the drum.

When the bridge travels to the left of the picture the arms extend fully. The bridge needs to move freely from left to right and as we try to move it by hand we must not feel any jamming point.

The bridge is secured in place by means of 4 black and flat metal pins. One can be seen at 11 o'clock of the right spool hole, one at 4 o'clock of the same hole, and two more towards the upper left and lower left of the left hole.

These pins can be pulled and removed if we need to remove the bridge but removing the bridge involves removing the capstan motor first.

Unfortunatelly, this doesn't appear to be necessary for this unit.

Towards the upper end of the bridge and to the right half we can see another set of racks. There we have the pinions of the tension arms. As the bridge slides the pinions rotate and the two part arms unfold following the slotted trace on the chasis to extend.

One of the faults I mentioned in before is having a tape mangled inside the deck and by pulling it bending these arms. Obviously it is the outer, steel part that is bent. If this happens the tension pulleys get raised and then the front tooth they have doesn't engage in the stop properly.

If we have such a case, we don't really need to dismantle the arms. Just a gentle application of pressure with the rubber end of a pencil in the middle of the steel arm starts to correct the bend. As always it is better to do that in small steps, each one bringing the arm closer to flatness.

You might have noticed that there are two springs inside the bridge close to the rack&pinion mount of the arms. This might not show clearly in the pictures but the springs are attached on the bridge at one end and to a sliding plastic part at the other end. The sliding plastic part contains the rack. The spring forces the rack to move with the bridge rotating the pinion and extending the arm. But, if the arm is jammed for whatever reason, the spring extends and the arm stops extending. The other arm - if unblocked - continues to extend. One of the deck's I've seen had the whole assembly for one arm dislocated and the rack was disengaged from the bridge. This is one case when the bridge needs to be removed - and so is the capstan motor.

The two arm pinions are secured in place by two small round clips. One should be black and the other white. At least that is what I've seen so far. But not on this deck.

There are a lot of such clips - on the undercarriage - and one problem with them is they tend to go and the part that is secured - especially the arms - gets further dislocated. If this happens and the owner of the deck continues to try to load and eject tapes it is very likely that the steel part of the arm will jam and bend. Have seen this - haven't seen anything break yet.
 

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The undercarriage

The undercarriage (again my own invented term) houses the two auxiliary motors, the reduction gears for the bridge slider, the reels and reel direction selector as well as two solenoids.

Again the first picture shows an overview and the remaining pictures show detailed closeups of the "usual suspect" parts.

To the top left we see the spool motor. To the right we have the bridge motor attached to the 4 reduction gears (2 black - 2 white). Then we have the two spool shafts with gears and between them we have the direction selection gear driven by the belt.

The black solenoid controls breaks and back tension and the black one appears to break the bridges shifting and release the spools and vice - versa.

We now have reached the heart of my problem... Let's describe the spool function in detail.

The spool motor rotates either clockwise or counter clockwise.

When rotating counter clockwise and the belt transfers the rotation to the spool direction shaft (between the reel shafts), it ROTATES that shaft to the same direction bringing the center gear in contact with the appropriate reel shaft. It then enganges that shaft rotating it to the correct direction.

So, when the motor rotates counter clockwise the center gear slides to the left and turns the left spool counter clockwise.

When the motor rotates clockwise, the center gear slides to the right and rotates the right gear clockwise.

In order for that to happen, the yellow solenoid needs to release the breaks. When the tape stops the breaks are engaged.

The breaks are the two black arms sitting on top of the spool gears as we view the picture. When the solenoid engages (pulls the rod inside) the black arms push against the spool gears. I don't know if it is clear in the picture, but there are friction pads where the break arms touch the gears. On one machine the sluggish FF/REW was caused by glue bleeding from the pads and causing additional friction with the shafts.

By removing the arms and thorougly cleaning them the problem was eliminated. I replaced that pads with a tiny piece of friction lining for the Revox breaks. It works fine.

Some comments on the close ups:

The first close up shows the gears. It is visible there that there is dust and debris accumulated between them. It also feels clogged. They need to be removed and washed.
The third picture shows a detailed view of the spool direction selector. The steel shaft houses the gear accepting rotation from the belt and the lever that houses the crazy gear that attaches itself to either of the spools. In the picture it is shown attached to the take up spool.

One mystery is why decks that show sluggish FF/REW/PLAY unload the tape (by rewinding the slack tape back to the supply reel) perfectly ok. I am suspecting that such a behaviour shows that the gears engage ok and shafts as well but only if the solenoids allow them to do so.

The fourth picture shows a close up of one of the many round plastic clips securing the various parts on shafts. If when you shake the deck you feel small things rattle inside, open the deck carefully and look for the offender. It might be one of those clips. Don't loose them - I haven't been able to figure out a suitable replacement myself. I've almost used all the clips from a donor machine that was shot.

The last picture shows the yellow solenoid and the back tension adjustment screw. Actually the transport chasis has room for two such screws but all decks I've seen and the service manuals only show one. Strange. This screw is one of the last things to adjust. Remember the holes I was mentioning on the cassette loading mechanism white flywheel? (OK you can look back at that posting). They are there to allow setting the back tension screw with the whole thing assembled. Some models that house the transport to the far left even have a hole in the base chasis to allow a (long) screwdriver to pass through...
 

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I had a sluggish DTC-59ES that I sold off in early 2000. I hear that there were some problems with that model of transport. So far my 75ES is ok. I also had a A7 that has the sluggish transport too. Good luck, you have more patience than me. :music:
 
I had a sluggish DTC-59ES that I sold off in early 2000. I hear that there were some problems with that model of transport. So far my 75ES is ok. I also had a A7 that has the sluggish transport too. Good luck, you have more patience than me. :music:

The same kind of problem is found on several of the mechanisms used in DTC57, DTC 59, DTC670, DTC690 and DTC ZE700. All these decks use the same transport with minor differences on the first two models. There must be other models out there sharing the same transport, just haven't seen them all.

I've seen recent (2002) builds of the transport suffer and old (1994) versions work flawlessly. I'm thinking of taking two such units and exchange parts to see what is the offending component.

I am suspecting the pressure pads (has been proven to be the cause in some cases) a weak spooling motor, a weak release solenoid (the black one) or gummified lubricant. It could also be a combination or all of the above depending on the condition of the unit. One was totaly cured by soaking it in hot water with detergent (just the undercarriage), rinse with de-ionized water and then baking it at 40oC to dry.

I do have patience in fixing this. My wife likes to solve crosswords I find that a waste of time. Others might find what I do a waste of time. But after working with computers and software for 20 years, the revival of this new hobby - combined with now being able to fix things rather than brake them worse 0 - is refreshing...
 
I do have patience in fixing this. My wife likes to solve crosswords I find that a waste of time. Others might find what I do a waste of time. But after working with computers and software for 20 years, the revival of this new hobby - combined with now being able to fix things rather than brake them worse 0 - is refreshing...

I'm right there with you SaSi. The fixing part of this hobby just started for me less than three years ago. I'm self taught.

My wife likes to do needlepoint and cross stich. These hobbies between the two of us gives us enough space that we don't drive each other crazy after 13 years of marriage.:rant::smilemad::twak:

She used to give me grief over buying up all this equipment but now realizes it's my thing, the cost doesn't add up to what she spends on herself with trips to see her family and at least I'm not out rabble rousing and boozing. Not that I'm inclined to do that anyway, but it's a point in favor of my argument.:D

I get tremendous satisfaction bringing something back to life that has been written off. Especially when I have to improvise due to parts availability.:rockon:
 
Cleaning time

Back to the unit now. I removed the 4 reduction gears. The way to do it is unscrew the small brass screw that secures the top black gear. Then remove them one by one. In order to remember how to put them back together, remember this. They go (from motor to the end) white-black-white-black (and the last one get's screwed in).

The double gears fit last and the simpler gears go in first. It's easy, especially having the pictures reminding us how they fit.

Removing the first gear (the one with the screw) was hard. Whatever lubricant was there initially was gummified and had turned into sticky glue. Gentle but firm rotations and some pulling solved it.

The other three gears were easier to remove but were certainly less free to rotate than I usualy see these.

I saved the screw and soaked the gears in water with detergent overnight. As the same time I cleaned the shafts with qtips and alcohol several times until I could feel them clean.

The rest of the transport's undercarriage I cleaned by spraying with alcohol using a focused vaporiser. I let the alcohol drip off to the sink.

All that happened Thursday night. I went back to to work with the unit this morning.
 

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Reassembly and testing

I don't know if anyone wants the assembly process documented. It is exactly the opposite of disassembly. I don't want the thread tediously long so for now I skip pictures of the reassembly process - unless anyone asks for them.

Now, there are some good news and some bad news.

The good news is that the clogging of those gears was responsible for inhibiting the pinch roller touch the capstan. Remember, those gears move the tape load arms and a bit further it enganges the pinch roller.

The transport operates like a charm. Excellent FF/REW, stable and without moaning and also playback. Audio is reproduced and all seems to work.

The bad news is that the transport exhibits a new (for me) kind of problem. I need YOUR help and suggestions here.

The pinch roller seems to pull the tape up or down against the capstan and eventually the tape is disengaged from the capstan. I have seen this problem in the past with seriously deformed and hard pinch rollers on cassette decks.

I don't have a new pinch roller but I do have 3 spare ones from transports sitting on the shelf with sluggish FF/REW but good play capability. I tried to exchange all of them and use them in the transport under test but the same problem persists. It looks like some pinch rollers will pull the tape up and others will pull the tape down.

This appears to be something to do with the capstan and pinch roller not being totaly parallel to each other. It could be caused by a deformed pinch roller but at least 2 of those I tried are ok (not only visually but after testing on decks).

I will be taking close up pictures of the test and the transport under test and post them later on in the day. For now I welcome any possible suggestions.
 
My DTC-59ES did "crinkle" the tape by having the tape slide down the capstan. It only seemed to be a problem at the beginning of the tape and not all tapes had this problem. I don't have any solution, but for some reason Sony seemed to have this problem with thier DAT and Cassette transports as I had a TC-K679ES cassette deck do this too. I seem to recall the pinch roller was "bowed" outward in the center and thought that was strange.
 
The pinch roller seems to pull the tape up or down against the capstan and eventually the tape is disengaged from the capstan. I have seen this problem in the past with seriously deformed and hard pinch rollers on cassette decks.

Well I have make in the past a new 'pinch-roller' for an old cassette-deck.
I have a couple dozen rubber's as spare part for some water-tap's.
The nearby look-a-like rubber I could used for the pinch roller.
So I did it cost me a half-day before it has the dimensions of the old rubber,

I drilled and grinding the rubber for several hours,
before it has the right dimensions, and when it was parallel to the capstan.
It did the job.

So I do it also for my Sony DAT (R300) if this occur in the future.
 
Pinch Roller problem

As I see it, you are suspecting the pinch roller. That's exactly what I did and that's why I replaced it with others, known good ones.

I am attaching two pictures of the pinch roller that causes most of the trouble.

In the second picture it becomes more obvious that the friction surface isn't flat but convex. This is actually the opposite of what vincei described and I've seen some other pinch rollers having a curved surface. Mainly small ones but also the ones on the Technics RS-15xx closed loop.

I am guessing that the curved surface allows for it to become flat once pressure is applied and this DAT transport certainly applies much pressure. The pinch roller is enganged by means of a motor rotating at high speed and the 4 reduction gears converting rpm into torgue. I can see the gears slowly turning as the roller engages, ensuring an even firmer contact.

I am now guessing again that a convex surface on the roller makes pressure at the central part uneven and uncertain. This might be the reason that the tape is grabbed by whatever part of the roller makes better contact.

In order to prove or disprove that, I reversed the roller (it is symetrical). Now the tape curled under the roller but not as often as before. And yes, it is more likely (almost certain) to happen at the beginning of the tape.

One more thing is that I tend to use scrap tapes with these tests. They have been mangled once or twice at some point of the tape and have several other problems, basicaly not good tape.

Fast forwarding (yes the deck can do that now) to the middle of the tape, things get better.

Another problem with this transport is that it doesn't provide good back tension. In fact I wonder if it does back tension at all. I see the tape slacking at the rollers and the characteristic reflection from the tape surface changing as it travels showing that the tape isn't pulled back constantly.

This is a different type of problem (actually a calibration matter) and I'l cover it later, for now we need to establish operation where a good tape doesn't get mangled.

I will try grinding the roller a bit, take pictures and report back.
 

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SaSi, on the pinch roller problem, check the tape tension. Too loose and it will ride up or down. Check the takeup clutch and the backtension band. Most likely the backtension.

EDIT: Just noticed that you don't have backtension. That's your problem.

Unfortunately I cannot see if the mechanism is using a brake band or clutch to tension the tape. If it's a clutch, make sure you put the reel tables back in the same order. Usually the clutch is in the reel table, and locked by a cog.

Well, you'll figure it out when you see it.
 
SaSi, on the pinch roller problem, check the tape tension. Too loose and it will ride up or down. Check the takeup clutch and the backtension band. Most likely the backtension.

EDIT: Just noticed that you don't have backtension. That's your problem.

Unfortunately I cannot see if the mechanism is using a brake band or clutch to tension the tape. If it's a clutch, make sure you put the reel tables back in the same order. Usually the clutch is in the reel table, and locked by a cog.

Well, you'll figure it out when you see it.

Well, I did: When I disassembled the undercarriage, I removed a tension spring connecting the two white arms that press against the spools. I didn't put that back on. The result is that there was no friction against the spools, solving the sluggish FF/REW no PLAY but as there was no tension hell broke loose with the pinch roller. I saw that as soon as I opened up the unit again.

Conclusion: Don't work on fixing things when you are tired and sleepy. You will make silly mistakes you won't even suspect you did. I know I did...

So we are back with perfect tension, all my pinch rollers are running well but running sluggish for reasons unknown. At least I have it where I want it. Causing the problem I want to solve.
 
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