Servicing a SONY DAT machine (Pictorial)

[jascha]

Good job, the shot looks pretty good.

If the ffwd test is positive and the tapes play on other decks we can conclude that the alignment is conclusive.

Concerning the monitoring on the 2700 I don't have any idea.

That's great news. Thanks to you and other contributors I managed to fix 2 machines it seems. I have a 3rd one lurking around, a PCM 2300 but I fear the head is shot as I get very weak output from the pbrf test point. I might give it another go and perhaps check the caps on the rf board? Practice makes perfect I guess.

 

[hdrobien]

As you have already probably noticed the mechas are almost identical.

I assume heads are clean and connections are good.

You can try first to swap the rf amp and see what happens on the scope.

Then you can swap heads (I have to check if you can swap the whole mecha)..

 

[jascha]

As you have already probably noticed the mechas are almost identical.

I assume heads are clean and connections are good.

You can try first to swap the rf amp and see what happens on the scope.

Then you can swap heads (I have to check if you can swap the whole mecha)..

I did try swapping rf amps but the other way round, in other words trying the rf amp from the 2300 onto the 750. I didn't see any different results at the time I was fiddling with the 750.

I shall try cleaning the heads and see what happens too. The mechanics are totally identical in fact to the 750. The electronics are mostly identical too it seems. I never swapped a head. Would it involve any alignment apart from of course the usual guides if they will need to be checked? I was just wondering what the DGP setting is for??

Thanks

 

[hdrobien]

If the rf amp of the 2300 enabled music on the 750 I assume it is ok. Anyway as far as I remember this model is not concerned by the bad capacitors disease.

If you take the heads from the 750 to use on the 2300 you will have to set the alignment on the 2300. You won't have anything to do on the 750 if you return the heads.

 

[jascha]

I see. How does the head come off? Is there any part of this forum that discusses the head removal of these Sony machines? I don't recall this being discussed on this thread, but I might be wrong. Any desoldering that needs to be done? Thanks

 

[hdrobien]

You have to unplug 2 sockets: the one on the rf amp for the signal and one from under for the motor (need to "open" the mecha).

Then just screws.

 

[jascha]

SONY 77ES DAT MACHINE in Need of Help

Hi, I have been given a lovely 77ES machine recently from a friend of mine and unfortunately this machine has been dormant for probably 10 years at least. It lived in humid conditions in Malta and due to it being faulty it has probably not even switched on for all these years. I am told that years ago it started behaving erratically, such as stopping during recording, opening and closing the cassette door on its own during playback or record and stuff like this. I just picked the machine up to have a look at it briefly and most of the operation buttons are non responsive. Not even the eject button is responding to opening or closing the door. It briefly displayed the words open and close but without any signs of motion. This only happened once however. Furthermore I can hear one or more than one of the relays on the lower board clicking madly when the input switch is either on coaxial or optical input. The word caution in red is displayed on the display.
I opened up the machine and also took off the bottom panel and could see signs of corrosion on the inside of the bottom metal plate and I suspect that humidity and local damp climates did not help matters to this machine.
I am taking the machine with me back to UK next week to try and get it going again however I find myself on the forum to ask for help please in helping me locate these faults.

As I have a PCM 2700 handy I am wondering if the boards are identical to the 77ES which would therefore assist me locate faults buy swapping boards around one by one? I suspect that there is some short somewhere, due to the humidity the machine had to suffer from, particularly the control panel board perhaps, which I have not dismantled yet and can only do that next week once I am home again and have access to my tools. The machine can do with some contact spray perhaps, to clean all the contacts first. It will be the first step I will take to eliminate any suspicious connections.

I appreciate your expertise once again please to try and get this wonderful machine complete with wood panels back to life.

Thanks

 

[hdrobien]

I will have to go deep in the service manual to check which boards can be swapped but as a start:
- check the power supply outputs
- spray deoxit on operation switches (remove the printed circuit board from the front panel)
- spray deoxit on all switches on the mecha

You will probably have to deep service the mecha in order to remove all hardened grease, especially on guides loading gears.

 

[hdrobien]

You can also swap the mechas.

 

[jascha]

Thanks. The mechanics I guess would not interfere with the operations of the buttons. At least the Play/Pause and Record buttons should light up as they have lights on them. Or do they light up only with a cassette inside? I cannot insert a cassette as the door won't open and therefore cannot load a tape. You are right in thinking that cleaning with contact cleaner is essential and will do that. Might sort out all the problems, but if you can assist me regarding which boards can be swapped this would be of great help. I just hope it's not some multi pin surface mount IC!

 

[hdrobien]

Sometimes bad switches on the mecha can turn crazy the control cpu because they send incoherent information. That is why it could be interesting to swap the mecha.

I think it is the first thing to try (if the 2700 is fully operational). If the 77ES works then right the problem lies within its own mecha. If not check/clean switches and connections. From my experience 95% of the problems come from the mecha.

 

[jascha]

Do you mean swapping the mechanical part of the DAT machine? (the whole transport section)? That's easy to do. It will be interesting to know if all boards on both the PCM-2700 and the 77ES are interchangeable and I can swap them around. My suspicion is that the problem is around the control panel. I can try to do this experiment next week when I go back home with this machine. I did disconnect the transport cables from the digital board but I did not see much difference in the behaviour. At least the eject button should work I guess?
Will be an interesting project for sure to find this fault
Cheers

 

[hdrobien]

You just swap the whole transport section. They are identical.
No time yet to check about boards interchangeability.

 

[jascha]

The 77es met my pcm 2700 yesterday! Interesting exercise and will try to summarise what I have found out so far!
I opened up both machines side by side! Looked at the digital boards, mostly identical apart from some connectors missing on one and not the other, but identical enough to swap around for testing.
I took out the two transports and swapped them around. The good transport of the PCM 2700 placed in the 77: door opened and loaded tape. Playback meters work and good sound from headphones! No other functions work. The only button that responds is the counter mode! Testing the 77 transport in the PCM electronics: transport failed, caution in red displayed on LCD screen.
I tested the tape drawer loading motor of the 77 transport by just plugging the 5 pin cable onto the 2700 digital board. The drawer works.

I then swapped around the digital boards and tested the 2700 board inside the 77 with the 2700 transport still inside the 77 & again I could only use the play function and eject the tape!
I have come to the conclusion so far that there are 2 issues here at least, 1st being the 77 transport and 2nd the control board of the 77. I think the digital board is good.
I hope my analysis is good so far and will dismantle the control board of the 77 as I suspect trouble from perhaps humidity conditions and some cleaning might help. Might try swapping control boards of both machines to see what happens as well.
I am not sure if I can conclude already whether power supply board is ok and audio board is ok as well. My instincts are pointing me at the control board and a dismantling and cleaning of the transport mechanism. Any thoughts please?
Thanks again

 

[jascha]

Update: following my earlier post I decided to try the control board of the 77 onto the 2700 deck and can confirm that there is an issue with the control panel board. I did some further investigation and discovered that 2 of the 4 surface mount electrolytic caps do not measure any esr! A third one measures high and the 4th one is on the limit! The bad news is that one of the caps seems to have leaked and corroded the board in a small location but enough to give trouble! I shall replace the caps and clean the board and try and make sure that the tracks are all ok and see what happens. It's a challenge and again a pain due to these sm caps!
What's your verdict please? I just hope it's not any of the surface mount ICs! Cheers

 

[hdrobien]

You can try to use tantal smd caps. They are as small as the electrolytics but a little bit easier to solder as their connectors are on the side, not under.

 

[jascha]

So far so good with 3 of them! The 4th one is going to be the tricky one as there seems to be track burning or maybe it's just black and needs to be cleaned off. Definitely those caps were no good as there were sizzling sounds during desoldering and a pungent smell of whatever liquid is inside! I hope this exercise will pay off. Will update you with some good news. Thanks again

 

[hdrobien]

Are you sure that there will be enough room for the new capacitors ?

 

[jascha]

I just tested the board to see if it fits with work I have done so far and success . I only needed to bend the one on the lower side on the left of the LCD screen. Now comes the 4th one and challenging one due to the burning colour around it. Hopefully the caps replacement will sort out some issues.

 

[hdrobien]

Well done, this deck desserves it.