R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 3 [4]   Go Down

Author Topic: Studer A80 Mark IV Slowing down  (Read 2420 times)

radardoug

  • Full Member
  • ***
  • Offline Offline
  • Posts: 100
  • Real Full Name: Doug Jane
Re: Studer A80 Mark IV Slowing down
« Reply #45 on: May 25, 2017, 04:53:24 pm »

I think you are onto something there. Pin 6 of IC3 should go high with slowing down, that would be correct.
But if pin 6 IC4 is already high, it would indicate that stage is trying too hard, and then runs out of steam. So the problem is following IC4. Try R48, the zener D8 (sus), and Q10.
Logged

radardoug

  • Full Member
  • ***
  • Offline Offline
  • Posts: 100
  • Real Full Name: Doug Jane
Re: Studer A80 Mark IV Slowing down
« Reply #46 on: June 05, 2017, 07:40:34 pm »

Mikeyod, any joy on this??
Logged

Mikeyod

  • Newbie
  • *
  • Offline Offline
  • Posts: 38
  • Real Full Name: Mike O'Donnell
Re: Studer A80 Mark IV Slowing down
« Reply #47 on: June 06, 2017, 09:40:26 am »

Hi Doug thanks for asking !
I changed all those components but no luck.
I felt like I needed to look elsewhere for the problem. So, I measured the voltages at the spooling motor transistors. The right hand voltage was always 5.8 volts which to me meant it was working as hard as it could all the time. After changing the diode bridge and the 68 ohm current limiting resistor it came up to about 12 volts, only at the beginning of a reel. When I changed the diode bridge and resistor for the other side things really started happening, the machine tensions went all over the place. After resetting them I had 25 volts on the right side. Today I'm going to change the 10 ohm resistors that are right on the RCA411 spooling motor transistors and see what happens.
  The manual says for 1.080.384 card. Stopped 126 volts, I get 165. Play 65 volts, I get 25 volts.
Rew/Ffwd 6 volts, I get 5.8 volts. So, I'm trying to make heads or tails out of this.
What do you think ?

Thanks, Mikeyod
 
Logged

radardoug

  • Full Member
  • ***
  • Offline Offline
  • Posts: 100
  • Real Full Name: Doug Jane
Re: Studer A80 Mark IV Slowing down
« Reply #48 on: June 15, 2017, 06:06:37 pm »

Hmm, from your symptoms, I would still say that it is the capstan card that is at fault. I haven't got around to measuring the same parts on the one here yet. Interesting that things improved greatly when you changed the reel bridges. Can you try running the old bridges under load on a d.c. supply? Some of these things will measure fine on a meter, but fail under load, with higher than normal saturation voltages.
Can you revisit the capstan card and see if you are getting right voltages there now? 
Logged

radardoug

  • Full Member
  • ***
  • Offline Offline
  • Posts: 100
  • Real Full Name: Doug Jane
Re: Studer A80 Mark IV Slowing down
« Reply #49 on: June 16, 2017, 11:54:46 pm »

Mikey, thinking about it it could be a tension problem, at higher speed the motors need to turn faster so will need more drive. Do you have a tentelometer? Check tension at stop, then 15, then 30. If the takeup tension is lower at 30 that would point to a problem with the drive circuit on that side. I am going to Auckland next weekend and will check on the Studer there. The capstan card checks out fine here, all values around that output are correct. There is one Frako cap on the power supply on the board, mine metered sort of OK but I changed it anyway. It is 20 volt decoupling so I dont expect it would have been the issue.
Logged

radardoug

  • Full Member
  • ***
  • Offline Offline
  • Posts: 100
  • Real Full Name: Doug Jane
Re: Studer A80 Mark IV Slowing down
« Reply #50 on: June 25, 2017, 10:24:18 pm »

OK, so spent some time on the Studer yesterday. We had a tension problem where the machine was pushing tape up on the exit roller with high tension, so I had pulled the tension down. Ended up replacing the pinch roller and retensioning and it was going great. But we decided to run it through a whole reel of tape, and the problem came back! Doh! However tensions remained constant and correct once the fault showed up, so I am back to it being the capstan motor. I ran out of time so will have to go back to it on another day. Our card checks out totally, so first up I am looking at the power transistor.
Logged

Mikeyod

  • Newbie
  • *
  • Offline Offline
  • Posts: 38
  • Real Full Name: Mike O'Donnell
Re: Studer A80 Mark IV Slowing down
« Reply #51 on: June 27, 2017, 09:39:22 am »

Hi Doug,
Sorry, my computer has had a serious bug and I haven't been able to get on line.
Did you get 180 volts on the capstan transistor and 80 volts nominal while it was running?
I'm only getting 130 and 40-45 volts while it's running.
  Another thing I have noticed is spooling motor control board 1.080.384-12 R53 (68 ohm 5 watt, right spooling motor) is so hot you can't touch it for more than a second. But R 57 (left spooling motor) is only warm to the touch. I wish I could have asked while you were there if this was normal but it doesn't seem like it should be ?
Logged

Mikeyod

  • Newbie
  • *
  • Offline Offline
  • Posts: 38
  • Real Full Name: Mike O'Donnell
Re: Studer A80 Mark IV Slowing down
« Reply #52 on: June 28, 2017, 02:28:25 pm »

The tensions are the same at 30 as they are at 15. They are right at the numbers in the middle of a reel right=450 left=300. At the beginning of a reel they measure right=475 left=300.
at the end of reel right=425 left=325. So a little higher on the side that is full of tape.
Logged

radardoug

  • Full Member
  • ***
  • Offline Offline
  • Posts: 100
  • Real Full Name: Doug Jane
Re: Studer A80 Mark IV Slowing down
« Reply #53 on: June 28, 2017, 07:44:47 pm »

The supply side 68 ohm will always be cooler then the takeup, because of the tension difference. But it could also indicate low gain in the output pair of transistors. The fact that your tensions are good takes us right back to the capstan control. Did you change the output transistor on the capstan control? The low voltages you are getting on the output stage would suggest a supply problem before this.
Logged

radardoug

  • Full Member
  • ***
  • Offline Offline
  • Posts: 100
  • Real Full Name: Doug Jane
Re: Studer A80 Mark IV Slowing down
« Reply #54 on: June 28, 2017, 07:47:13 pm »

By the way, you need to be looking at that on a scope, it will read low on a voltmeter.
Logged

Mikeyod

  • Newbie
  • *
  • Offline Offline
  • Posts: 38
  • Real Full Name: Mike O'Donnell
Re: Studer A80 Mark IV Slowing down
« Reply #55 on: July 10, 2017, 03:26:01 pm »

O.K. I have replaced every Resistor, I.C. , Transistor. All Electrolytic caps, All tantalum caps andR45 potentiometer on board .372 capstan control. The 8 uf motor cap and the rca411 transistor off board, and had the motor rebuilt.

That only leaves the ceramic caps and the poly/film type caps. and R27 5k ohm pot.

It still does it.
Logged

Mikeyod

  • Newbie
  • *
  • Offline Offline
  • Posts: 38
  • Real Full Name: Mike O'Donnell
Re: Studer A80 Mark IV Slowing down
« Reply #56 on: August 11, 2017, 02:29:37 pm »

I have used this machine for 5 days and it has not slowed down once !!
Although I hesitate still, to call it fixed (You know how these gremlins are).
After I replaced all the poly/film type caps (except c11 3.9nf I could not find a suitable replacement). I got tired of doing one item at a time and just changed them all at once so I don't know exactly which one did it. Also, before I was able to check if this worked the stabilizer card went south and I had not even been able to turn on the machine. Once I repaired this little gem of a problem ( I wonder also if this imminent failure was the cause of the slowing down ? ) now it seems to work and I have been able to get these mixes under way.

I have got to get better at troubleshooting !! Or just start replacing stuff wholesale. 
Hopefully another ten years without having to solder on the Studer is in my future !!
Oh yeah, I still gotta figure out the PoP in my A810 in my other post

Thanks to Doug for the help and sticking with me through this.
Logged

radardoug

  • Full Member
  • ***
  • Offline Offline
  • Posts: 100
  • Real Full Name: Doug Jane
Re: Studer A80 Mark IV Slowing down
« Reply #57 on: August 13, 2017, 02:48:09 am »

Nice to know you might have it fixed Mike, I haven't got back to the one I'm looking at.
Logged
Pages: 1 2 3 [4]   Go Up