Servicing a SONY DAT machine (Pictorial)

[Kabal]

SONY DTC-670 reel motor speed changes during playback and mute relay clicks.

Hi,

I have 2 pcs of DTC-670 which I have serviced. First one was easy - I have cleaned the mechanism , glued felt pad , changed reel motor to new one [RF-300CH-14440], added 22k potentiometer, and it has been working OK for the last year or so. Even on DDS1-90m tapes.


Second deck, same model , gives me hard time. There was no sound - fixed by changing the RF amp caps. Cleaned the mechanism, fitted new cat washers on the reels (supply & take-up) and still didn't work properly. Somehow the take-up spool was higher than the supply reel and IR sensor did not pick up the black & white pad so take-up was stall. I have cleaned sensors and pads underneath reels and mechanism started to move properly. Also fitted 22k potentiometer as per service manual. Sound it there, clear and perfect, but once per 30 seconds or so the mute relay starts to click and music cuts off. I have observe the reel motor and belt for the whole time and while the relay starts to click the motor starts to speed up (like it tries to catch up?) and then settles with constant speed again for the next 30 seconds. ... and the story goes on and on.


Any ideas? Maybe caps on the drum board? Appreciate your help.

 

[hdrobien]

If the reel motor starts to speed up it means the clutch is slipping. Maybe too much torque but I can not see any direct relation with the relay.

I can't understand the point concerning the take up spool higher that the supply reel. Any pictures ?

 

[Kabal]

Hi,

The take up spool is on a spring (364) and this was 2mm higher than the left spool. I have drilled a small hole in my test tape and by pressing the spool from above I saw it was moving. Somehow the IR sensor didn't pick up the white&black stipes underneath the spool. I have compressed the spring and both spools are horizontally aligned.
However what concerns me is the clicking of mute relay (switch?) and music cuts. One of comments

under the video from Niciodata Pierdut is about same thing.

What I am planning to do today is to take out the mechanism again and fit it into good unit and see if the same thing will happen. If not my guess would be to change some elect. caps on IC311 (servo).

 

[hdrobien]

Both spools are nearly identical. The only differences are some washers to modify the "not detailed" spring strength. This spring controls the slippage of the clutch embeded in each spool.

Each spool height is "locked" by the washer #367 so I can not understand why they could not be at the same level, unless something is misplaced.

 

[Kabal]

#367 was not original one as in second deck I have. Therefore I have fitted one from where the brakes are and that has fixed the misaligned. Issue which persist is the clicking sound every ~minute coming from mute relay. The tape travels smoothly thru the mechanism. Maybe some cold solder somewhere on main board.

 

[kfalls]

This looks like a very detailed account of DATs. How do the players listed compare to the Sony PCM-7040? I work for a company who has 12-16. These can be very temperamental having errors one day then running the next. We currently send these out for repair, but I would like to eventually gain enough knowledge to work on them myself. Any advise or insight you can give on the PCM-7040 would be appreciated.

 

[hdrobien]

I have never had to deal with a 7040 which mecha seems to be based on DDS drives that are supposed to be reliable.

But I own a PCM-7010 (based on DTC-77ES mecha) and a PCM-7030 based on DTC-1000ES mecha. Beside typical DAT problems (dust, hardened grease, dirty heads...) these machines suffer from defective electrolytic capacitors, mainly on their switching power unit board.

 

[uzvarb]

I'm on a DTC -670 issue with the disappearance of sound found in poor solder places around wide ribbon cable that comes from mechanics.

 

[Impala-321]

Hello from Austria!
Please I'd need some help with my Sony ZA5ES which has exactly the same problem as described in post http://www.audiokarma.org/forums/in...machine-pictorial.184212/page-15#post-7709090.
I also noticed that the S1 guide would not go to the end position, there is a 5mm gap left. However in my case this is persistant ie even after 100 ejects and warming up of the machine there is no change of the S1 position (which most likely is the cause for the sometimes distorted sound during playback).
Has anyone an idea who to fix this?
I'll post a picture of the currently dismantled deck to show how far i got already.
Thanks in advance!
Kind regards, Harald

 

[Impala-321]

 

[hdrobien]

Hi
This is probably a common problem typical on this unit and other models sharing the same mecha.
A sliding part on one of the gear that drives the T1 guide becomes stuck with old grease and this stops the loading sequence too early.
This gear is one of the 2 large black rings that surrounds the drum motor, the one under, on you pictures.

 

[hdrobien]

Here is a picture of the rings of a PCM-2700A that suffered recently from the same problem.

You can see the sliding part (silver) on the upper side of the front ring.

Also check that the sliding arm of each ring slides smoothly.

 

[hdrobien]

Be careful as this is not a easy job to dismantle the mecha to reach the rings.

 

[Impala-321]

Wow, thanks for the superfast answer!
Yes this look tricky , i will have to unmount the capstan motor unit right?
Does this require reallignment of the deck later?

 

[hdrobien]

Yes, you will have to remove the capstan motor but it is not the trickiest part.

Get the service manual p.85

Here is the list of operations (once you have removed the circuit board of the mecha: be cautious with the connector for the drum motor it is fragile)
- remove the reel motor block M903 (3 screws)
- remove the capstan M902 (3 screws)
- remove the 2 washers #301 that holds T1 & S1 to their respectice lever #319 #321
- remove washer #311 to release gear #309
- uscrew the roller arm #304 that hold the rings together
- remove the rings, clean them, lube them lightly
- replace both rings (tricky) and fasten the roller arm
- reconnect each ring lever to their respective guide with washer
- put both guides in start position (beware there is a spring effect)
- you will notice a hole on both rings near the gear you removed, and another hole in the main chassis near the capstan. Use a small screwdriver to "align" the 3 holes. This will synchronize both guides
- while holding the screwdriver in the holes, replace gear #309 and its washer to lock positions.
- replace capstan, reel motor block, circuit board...
You are done !

You won't probably have to realign guides BUT the guides assemblies themselves usually get easily out of their socket as they are just "crimped". You have to try to pull them out to check. If you are able to remove the guide put a microscopic drop of glue or use pliers to make a mark on the brass part before re-crimp it.

This may require adjusting the setting of the tape path as it may slightly modify the height of the guide.

 

[Impala-321]

Thanks again, you are great! I finaly could avoid dismantling the rings. With your hint I located the slider which was stuck and used a tiny drop of alcohol and a screwdriver to make it moving again (very careful).
What should I say: It works and sounds like on day 1!!
Now I just have to use the recorder more often than in the past to prevent the grease to get hard

 

[hdrobien]

Good to ear that your DAT is working again.

But I would not recommend to try to unstuck the slider without dismantling. If you put too much strength you can easily break a tooth on the plastic gears that synchronize the 2 rings together.

 

[Gregory_67]

Hello Sa Si.

After several days of work, my first DAT DTC-670 is fully operational. All well known “illnesses” have been effectively fixed. Forward tension torque mod is applied too.
Many thanks for this great thread. It was very helpful.
There is only one thing puzzling me a bit.
I've been trying to find information about the motor propelling head drum but without explicit results.
Is it a brushless engine combined with internal driver like in VCR's or commutator motor with PG/FG windings connected to external servo?
Head drum assembly in my DAT is making noise very similar to the sound of working commutator motor.
Is it normal sound or not?

Regards.
Gregory

 

[hdrobien]

I would say that the head drum motor is similar to VCR.

Ans it should turn silently. Otherwise there is probably dust somewhere.

 

[Gregory_67]

I would say that the head drum motor is similar to VCR.

Ans it should turn silently. Otherwise there is probably dust somewhere.

Thanks a lot hdrobien for reply.
Nature of this sound is mechanical. I've checked today what is happening when deck is playing back the music and main power switch is pushed off.
Drum head is slowing down emitting metallic sound until it's completely stopped.
Settled file is the recording of working deck.

Gregory