Servicing a SONY DAT machine (Pictorial)

[hdrobien]

I just want to check my theory about tape trembling.

You can "open" the mecha to check the felt pads (used for play back tension) and the brakes, but I believe the problem is elsewhere.

The reels generate themselves some back tension as there is a spring underneath (part #364 on the service manual).

But lets be honest, I would not bother too much about the "tic tic" sound if everything is fine.

 

[d-roby]

Thank you, but i would like to fix it ;-)
i noticed that the right reel turned by hand has a little friction ( and it should be correct) but the left one turns freely.. Brakes?

 

[hdrobien]

It depends of the mode the deck is engaged in.

Each reel has several type of brakes:
- rubber ring to stop them from rotating after fast-forward and rewind. Strong friction (you can feel the teeth of the gear on which it relies). Activated with a plunger.
- felt pads for back tension during play and reverse play. Medium friction. Activated with a plunger.
- self friction with the spring underneath. Very light friction. Permanent.

Some say that the felt pads generate some friction even when they are not "activated" by the plunger.

AFAIR, in stop mode, the rubber brakes is only active on one reel.

 

[d-roby]

I checked the reels , brakes and clutch..everything seems to be fine..
But the problem is still present:
expecialy in rewind, the tape, as you suspected, is trembling, and i think the tic-tic is a solenoid,.. may be like a fast "start and stop" that of course change the speed of the tape..
BUT... i i use a blank tape FFWD and REW is ok... uhm....
is the solenoid adjustable?
Many thanks

 

[hdrobien]

No I don't think it can be a soleinoid, which sounds more like "clac".

I am pretty sure it is just the tape as it runs especially fast.

 

[d-roby]

If i reduce the "torque" with the trimmer, the tit-tic is less frequent , or disappear, but ,of course, the speed of rewinding is low....
It is a pity, as record and playback is fine.( i tested again).and the sound is very good, too

 

[hdrobien]

If it sounds good and rewind fast and secure, just enjoy !

 

[Dimitris_]

Hi Everyone!

With the help of this thread and the service manual I almost fixed a Sony DTC-55ES that I bought from eBay not very cheap with description “For parts or not working”


The machine had multiple problems:

Broken rotary encoder gear. Fixed with superglue

Old, sticky grease everywhere in mechanical parts. I remove it and apply new lubrication.

Bad pinch roller. I use another from an IBM DDS computer drive.

2 bad caps in RF board.

And it was completely uncalibrated. Not possible the playback tapes written from this machine to my computer DDS drive (with special firmware in order to read DAT tapes) and not possible to play tapes written from my DDS drive to Sony.

After 2 days fighting with the calibration guides, finally it’s ok!


Now I have 2 more problems and I need some help…

First problem is that sometimes the take up reel not starting when I press the play button and the tape get jammed inside the machine. At the same time the machine seems to sluggish to rewind the tape and I think these two are related.

Another clue is that the brake pads of the take up reel have more wear from the other ones…


Second problem is that the machine have a fade in / fade out function.

When using the headphones this is working as expected. But when using the optical digital out it’s not working…
Only the counter starts and the bars shows the progress of the fade in or out but the sound volume doesn't follows... its on or off

I don’t believe that it’s supposed to be like this.


Any help guys???


Thanks

 

[Blink1]

Hi,

Mine has the same issue with the transport and it might be cassette related: try a different tape once. Or it may not as sometimes it works ok with the same cassette sometimes it doesn’t (Maxell 90 here).

The fade as far as I know only works over analog, check your manual please.

 

[hdrobien]

@dimitris

Regarding your first problem, I would suggest to replace the felt pads of the "lever (slider) assy" (part #562 on the schematics). Of course it implies that previously you cleaned all old grease.

 

[RMbA]

Incredibly impressive how much knowledge and skill is covered in this thread—Sasi's especially, of course, but many others as well. Thanks to all.

I recently acquired a DTC-790 for next to nothing. I don't know any of the machine's history.

The unit powers up and the cassette door opens and closes normally. However, when a tape is inserted and the door closes, none of the transport functions work, so the tape will not play, fast-forward, or rewind, and the mechanism won't eject the tape except manually.

With the cover off and the power on, it appears that the tape loads normally, wraps properly, etc., but the head doesn't spin. However, manually causing the door mechanism to operate, the head spins for a second or two. FWIW, when the head is spinning, it's absolutely quiet.

I'm wondering if there are micro switches in the transport assembly that have become stuck and might benefit from a shot of Deoxit.

Any thoughts or suggestions would be much appreciated.

I should add that my tech skills are barely basic, my tool kit is pathetically small, and my test equipment is a multimeter.

 

[hdrobien]

Hi

Once the tape wrapped around the head-drum, what happens ? Do you have any "caution" message on the display ?

Can you remove the transport from the cabinet (just 4 screws to remove) ?

If so, there is a black gear surfacing the front end of the transport. Try to rotate it with your thumb (It will extend or retract the guides around the head).

There should be some resistance but if you give a good kick there should be some inertia. If not there is probably some old sticky grease jamming the gears, switching the logic into security mode (this model is quite sensitive).

Another idea is that the end of loading sequence is not detected, so the heads are prevented to spin (never experienced myself).

 

[RMbA]

Many thanks for the quick reply. I think my wife may be coming down with the flu—we're elderly, so it's serious, and I'm not sure if I'll be able to follow-up on your questions and suggestions this morning.

But for the moment, I can say that there is a "Caution" message on the display.

I'll try to get back to it ASAP and see what's happening with the black gear on the front end of the transport.

 

[RMbA]

Nothing I can do for my wife at the moment, so I'm back at it.

First, either something has changed or, more likely, I was simply mistaken about the tape wrapping around the drum. When the tape is inserted and the mechanism closes, the tape is NOT wrapped. The guides move into place, as if they should bring the tape against the drum, but they don't. Bottom line, the guides are moving in what appears normal.

 

[hdrobien]

I don't undersand, sorry engish is not my native tongue.

Do both guides move, or no,t when cassette is inserted ?

If they do, how can they move without bringing the tape around the drum ?

 

[RMbA]

Your English is great.

I was trying to figure out the same thing—why isn't the tape wrapped around the drum?. And yes, both guides move when the tape is inserted.

This time when I took the tape out, I checked it and discovered it was damaged. Actually, it isn't my tape—it was the tape in the machine when I got it—and was probably damaged before I got it.

So, with another tape in the transport, the tape is pulled against the drum by the guides. But none of the functions work and I still have the "Caution."

 

[RMbA]

And I should have added that somehow I managed to ruin a new tape while trying to remove it from the transport!

 

[hdrobien]

Ok.

Keep in mind that the black gear surfacing the transport will extend / retract the guides. So if a tape is stuck with guides extended you can safely remove it (unless something is badly jammed inside)

Check the condition of inertia with the black gear. It is a very common issue with this specific model (DTC-790). Coincidentally I am currently servicing one and it suffers from this issue (among other things).

 

[RMbA]

Not sure how it should feel, but when turning the black gear it does NOT continue turning beyond pressure being applied directly to it. It's not hard to turn, but I would not say it turns "freely" at all.

 

[hdrobien]

If there is no inertia after a solid kick I would go for a cleaning of old grease.

If you are a little handy, it is not that difficult. You need a small phillips screwdriver + alcohol + cotton swabs + nail lacker.
- remove the transport from the casing (4 screws)
- turn it upside down (don't need to remove the loading frame)
- remove the 2 screws at the back, in the angles of the printed circuit board
- remove the shiny screw on the front (near the black gear)
- remove 3 black screws holding the upper part of the transport (lower in fact as the transport is upside down): one near the motor with the orange toothed belt, one in a front angle, one in the middle (not the one on the printed circuit board)
- open the transport in 2 halves (cables will keep them together)
- locate the 4 gears assembly (2 black 2 white) on the upper left angle
- remove the screw holding the upper black gear and clean its shaft and axle from old grease RED CIRCLE
- remove the upper white gear and clean its shaft and axle from old grease. RED CIRCLE
- put the 2 gears in place, with the screw
- on the lower half check that the 2 white washers are in place on both gear with arm (one white, one black). BLUE CIRCLES
- if necessary push them back with your finger and apply some nail lacker on it (the washers are prone to go away)
- check that felt pads are in place on the brake levers GREEN CIRCLES
- close the transport. Push the long white lever in the front to help.
- check that it is in perfect place before putting screws back, especially the screw embossement near the motor with the orange belt.
- you're done !