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Servicing a SONY DAT machine (Pictorial)

I don't believe that this thread deals with the DTC 700 but with the following models.

This gear belongs to the rotary encoder which is located on the upper side of the mecha, on the right side of the headdrums (see the pictures in ebay to recognize it).

Remove the 2 screws, turn the encoder upside down and you will see where to put the gear.

Then there is a procedure to set the encoder. The procedure is described in the service manual.
 
I am pretty sure the mechanisms I've worked on and shown in the thread don't employ such a rotary encoder. I think the pictures on the linked ebay auctions show how to mount it and in what place in the transport it is located.
 
This rotary encoder is only employed on the DTC-1000ES, 55ES and maybe 300ES (and also PCM 7030).

It is the only weakness of these models that needs a a replacement part.
 
So that's the offending part that makes DTC-55ES non functional? Nice to know - I have three of these that need care and I need to attend to these at some time.

Nice to learn something every day...
 
From my experience the gear always breaks (or at least cracks) on those rotary encoders.

The rotary encoder synchronizes the guides/pinchroller loading sequence so the symptoms are easy to guess.

Most of 55ES also suffer from another problem: slow rewinding/unwanted stops.
 
hdrobien said:
From my experience the gear always breaks (or at least cracks) on those rotary encoders.

The rotary encoder synchronizes the guides/pinchroller loading sequence so the symptoms are easy to guess.

Most of 55ES also suffer from another problem: slow rewinding/unwanted stops.
Click to expand...

Have you figured out the slow ff/rew reason? Is it the same as with the other transports?

I have one DTC55ES that seems to be functional more or less but FF/REW stops abrubtly at random. The other two seem to have an issue sensing the cassette is fully loaded in order to extend the arms and load the tape. They just load the cassette and then stop.
 
Issues related to the loading of the tape are probably related to the rotary encoder but you have to be sure that all the gears of the guides loading system are totally free from old sticky grease.

Especially:
- the 2 circular large dented rings pulling S1 & T1 guides with their "spring arm",
- the F guide which, in most case, stays stuck fully extended.

Concerning the fast forward / rewind problem (in my case mostly rewind) you can notice that when rewinding near the beginning of a tape the reel motor automatically reduces its speed to avoid excessive shock on the tape. But most of the time the torque becomes insufficient to drive the tape and it stops.

I am not sure about the real cause but I have found a cure.

I first suspected a worn out reel motor but torque turned to be within specs in play mode and full speed rewind.

So I checked and cleaned path again, looking for any trouble .

Then I checked the back/forward brake/tape tension system which is a little complicated, as you can find:
- 2 arms with pads blocking both reels when not playing/rewinding/fast-forwarding
- A T-shaped slide lever with felt pads located between the reel and generating back tension on both reels, either in play mode or in rewind/fast forward mode
- A belt generating back tension on the supply reel, only in play mode

My understanding is that the back tension generated by the slide lever is excessive regarding the reduced speed of the motor, thus stopping it.

To reduce the back tension you can loosen the spring that presses the pads on the reels. But you have to find the right setting as the tape must stay tight during rewind/fast forward.

An alternative is to replace the felt pads by something less grippy. I think that this solution is more efficient once you have found the right material. In my case the best setting was to have a slighty thicker pad on the supply reel.
 
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Update

Just wanted to give everyone an update here. I purchased the rotary encoder gear that hdrobien recommended from ebay seller "dr._gear" which is currently listed at the following link http://www.ebay.de/itm/SONY-DAT-DTC-PCM-Digital-Audio-Tape-Rotary-Encoder-Zahnrad-Replacement-Gear-/321529224099?pt=DE_TV_Video_Audio_Sonstige&hash=item4adca29ba3. "Dr._gear" was very helpful and even provided instructions for the install from the repair manual. ("Dr._gear" can also be reached at dr.dr.gear@gmail.com). I was able to successfully install the gear without requiring any adjustments. Afterwards everything worked normally and I was greatly relieved. A repair like this at the local repair shop would start off with a $50 diagnostic fee and then probably another $40 for the gear and possibly another $50 in labor with a total cost of around $140 which makes the overall repair not feasible since a used player could be purchased with that amount. So with that said, I made a small contribution to Audiokarma and appreciate Sasi and hdrobien's help.
 
Hi All!
Great Thread!
Many thanks to Sasi and all the others!
I recently too acquired a DTC-690 with no movement in any direction, but still moving the S1 and T1 as it shoild when the tape is loaded.

So, I started to investigate the fault and pretty much went through all the stages you all describe here.
Drive mechanism is cleaned.
The guides are checked, OK.
Cam motor and the four cam gears moving the S1 and T1, checked, cleaned, olied axles, reassembled.
Timing belt, checked, left with enough slack/free play
Reel motor, checked, reel movement checked. Motor replaced this evening, just in case.
Retaining grommets/clips checked and thermal glue applied.
Felt pads, checked and adjusted the back tension with the screw on the side of the mechanics.
PCB checked thoughout, all solderings re-passed.
Head cleaned gently with alcohol and fine tissue.

After all this the result is: almost no movement or very slight movement of the tape in either direction after the tape is in.
Yesterday night I stayed up intill 1 PM to tinker with the DAT. And, out of the blue, the REW and FF suddenly came to life.
The I tried the PLAY and it worked too.
But not for long. Few tries after, and I was back to square 1.
Nothing again.
Then, I decided to touch the pitch roller just to make sure it is pressed properly in position against the capstan......and..........gues what - the capstain was not moving in PLAY mode. Tried to help by rotating the pinch roller gently, and the DAT Came back to life again. I did not stop it this time, connected a source and made a test recording. All OK. Then, after 15 min of recording and ID marking decided to rewind and check what I did.
And, no movement and reaction again.

So, I went to bed, and today after I got home I resumed the tests.
Changed the reel motor as I told you earlier, and the fault is definitely NOT there.
The blocking of the movement comes from the CAPSTAIN motor ASSY marked M902.
The capstain must engage and rotate forward a bit when the tape is in position and loaded, the head reads info, and the mechanim then reverses a bit, so the tape comes to its initial position. The capstain must reverse as well so to allow the reel motor to rewind the tape.
If you have noticed, the pnch roller is engaged almost constantly in all main modes - SEARCH FORWARD, SEARCH REVERSE, REW, FF, and PLAY of course.

In all those modes the capstain motor will go forward slow, forward fast, reverse slow or reverse fast.

It has 4 wires connecting it to the main PCB by a read connector placed in in the corner of the PCB, next the the mechanism. They are +5 V, GND, BRAKE, and DIRECTION CW/CCW input.

I tested all the signals and the ones needed to go to the capstain motor. There is feed of 5 Volts, GND is OK, the BRAKE goes from HIGH to LOW when PLAY is pressed, and the DIR signal goes from LOW to HIGH in PLAY mode.

Nevertheless the capstain does not turn.

Its driver IC is LB1617.

That is my situation in brief.

Any ideas and advise will be appreciated.

Regards from Sofia, Bulgaria

Radko
 
Hi

The capstan is only engaged (ie with the pinchroller) in play, fast play, reverse play, not in FF or REW or during track search (maybe it is turning but I doubt).

In you case it looks like a bad contact somewhere (solder ?).

Or, maybe,
- one of the coil of the motor is dead and it needs a little help to start turning.
- the capstan axle itself is stuck by dirt and it also needs a little help to start turning.

So my best advice would be to tear apart the capstan, check the coils, check the solders, check that it turns "freely" (beside the magnetic effect), clean it.
 
Hello hdrobien,

I will check again just to make sure, and will attach some pics and possibly video today of all the modes and the position of pinch roller to capstan.

I have not checked the capstan motor assy for bad solders. Will do it and report.

No, the capstan is not stuck, as it was disassembled, cleaned and a tiny drop of oil was applied on the top brass grommet bearing. The capstan itseld rotates freely and with little effort.

Have not checked the coils, there are six of them connected in pairs forming the three phases of the motor. Will check those as well.

Apart from that will connect power feed to the capstan assy when out of the mechanism and will check the control pulses and response from it.
 
Repair status update

Hi All!

Good news!
I got the DAT working, and the main mechanical problem was the capstan motor assembly. A friend gave me a spare one, from DTC-670, they are absolutely identical, and the DAT is alive.
All functions work correctly.
So, guys, apart from checking the tape driving assy and cleaning it, please pay attention to the capstan motor.
Also, if you see fit, replace the 22 Ohm / 1W resistor for the holding solenoid
with 22 Ohm / 5W one. This will guarantee a constant holding current for the solenoid, as the 5W resistor handles the power dissipation better.

One more problem to solve now. The deck plays OK all pre-recorded DAT tapes, no issues. No matter how long the tape is. All functions OK.

It records on its own OK, but when you rewind an try to play back the recording you made on the DTC, the deck loses the time code and the muting relay starts to cut off the output signal.

The record made on the DTC when played on another DAT deck, shows the same defect, i.e. sound is recorded with drops, which results in output cuts/mute passages.

Any ideas?

Thanks!
 
Hello hdrobien,

You think the recording head is gone?

Should I check the RF amp block and the capacitors there also?

And, how could I perform a test to be sure the head drum needs replacing?

Thanks!

Regards,

Radko
 
There are 2 heads on the drum.

Both heads are used for playing and recording.

From my experience when heads are dying, problems come first from recording.

But you can try to replace the capacitors.
 
Yes, you are correct.
I found a spare head today, hopefully this will solve the issue with recording.

Firstly, I replaced all the capacitors on the RF board, no change, no improvement.
At least I know now, it is not a fault in the RF board itself.

Will keep you posted.

Best regards,

Radko
 
Hi,
Did you touch back tension screw? I had the same issue a few days ago. One day recording worked, next day not. I remember that I played with back tension. Tried different screw position and it start record again.
I guess correct supply and take up reel tension is most critical setting when tape mechanic is overhauled.
That's why I am looking for torque test cassette. If anybody have one, will buy it :)
Cheers
Roman
 
Hello again to all!!!

With the spare head in my pocket, today I decided to swap the one in the DTC with the one I obtained. All pretty simple, at first. Dismantled the "old" head, disconnected the CNs from the RF and the drum control connections, unscrewed the three holding screws.
Replaced the head drum block, put all back together, and........... in PLAY mode there was nothing. No index search, back or forth, no sound, no reading of the initial info and time. Thought the "new" head was the problem, reversed the entire procedure, put the original head back in, connected everything, and......... again no sound, no idex search, no time reading.........
Mechanically, the DTC 690 is OK. Everything there works as it should. REW, FF and PLAY work. Index search Forward and Back engages, but no scanning.

To your question Roman - yes, when I serviced the tape mechanism, I adjusted the back tension, but by hand, no torque cassette present.

Guys, any idea what could have happened?

I will trace the signals tomorrow with oscilloscope, but this is very strange occurance, don't you think?

Best regards from Sofia!

Radko
 
I will check all in a day or two, will make pics and possibly short video, and will post them here.
Checked the RF amp, visually it is OK, I just disconnected the input connector, and the large output connector which goes to the main board, and that was to remove the tape transport mech. assembly.

Anyway, will post an update.

Regards,

Radko
 
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