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Author Topic: Studer A80 Mark IV Slowing down  (Read 1770 times)

Mikeyod

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Studer A80 Mark IV Slowing down
« on: March 28, 2017, 01:43:06 pm »

Hi guys,
I've got an A80 2 inch 24 track Mark IV and it has begun randomly slowing down.
After about a half hour the problem is gone and it runs fine.
What I have done/checked.
Stabilizer voltages all check out fine.
All motor caps have been replaced.
All motors have been rebuilt by Athan corp. in Jan. 2017
Replaced timer IC on capstan control board
While viewing the 1600 Hz signal on a scope with frequency counter the frequency drops to around
1300-1375 Hz the second I hit the stop button the frequency comes right back up to 1600Hz.
When the freq. drops the tape tensions on both sides remain normal 300 on left 450 on right.
However if I turn the left tape tension sensor manually and lower the tension down to 100 the frequency comes back up to 1600Hz but falls off again as soon as I release it. All voltages on the stabilizer card hold steady when the machine slows down. Like I said after about half hour I can go about my business as usual and it will not slow down.
Any thoughts ? Thanks in advance.

Mike O'Donnell
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radardoug

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Re: Studer A80 Mark IV Slowing down
« Reply #1 on: March 29, 2017, 06:40:57 pm »

Have you replaced the Frako caps on the cards in the card frame? They will probably start smoking soon if you haven't! I had an A80 with speed problems, this cured it. But I still have a problem with 30 ips I haven't sorted.
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Mikeyod

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Re: Studer A80 Mark IV Slowing down
« Reply #2 on: March 30, 2017, 10:04:50 am »

Yes, all of those caps have been replaced.
I tried running the machine from cold with the auto-locator unplugged to see if this could help narrow it down but the same result. After half hour it cleared up. I'm assuming something is warming up then functioning properly ?
   Could the LY4 contactor be a cause of this ? Looking at Mouser to see if it is still available.

Mike
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radardoug

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Re: Studer A80 Mark IV Slowing down
« Reply #3 on: March 30, 2017, 07:52:49 pm »

Are you running high speed or low speed?  If high speed, check it on low speed.
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Mikeyod

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Re: Studer A80 Mark IV Slowing down
« Reply #4 on: March 31, 2017, 10:45:31 am »

This is a 15/30 i.p.s. machine that I run mainly at 15 but I will try it at 30.
I took the contactor apart, the contacts were very fried. I am cleaning them up to see if it helps.
Meanwhile I ordered a new one if it does help.
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Mikeyod

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Re: Studer A80 Mark IV Slowing down
« Reply #5 on: March 31, 2017, 12:04:57 pm »

After filing away at the contacts on the LY4 contactor I have used the machine for the last 50 min. starting from cold and the machine did not slow down at all. Another thing I noticed is that the auto-locator does not miss the mark by several seconds and then jog itself into place. Of course this could all be coincidence and it will slow down tomorrow ;). I'm guessing if this is the cure then a brand new contactor will really do the trick, as these were real pitted and I had to take some stock off those contacts. Keeping them perfectly flat is difficult with a file and why bother really when a new one is on the way. We'll see.

Mike
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Mikeyod

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Re: Studer A80 Mark IV Slowing down
« Reply #6 on: April 02, 2017, 02:24:03 pm »

Further points of interest;
I have used the machine four times now after the first time I filed the contacts on the contactor.
The second time the machine did not slow down at all again but it began to miss the mark auto-locating. It would miss by about 1 second at first then it got to about 6 seconds.
The third time it started right away missing the mark by 6 seconds and about halfway through a song it slowed down. But, for the first time it sped back up to normal. I shut the machine off and pulled out the contactor and a couple of the contacts were blackened. A little bit of 220 sandpaper and they were clean. Put it back and it immediately hit the mark auto locating and no slow downs.
  Today ( fourth time ) the machine did not slow down but has started missing the mark locating. It started off with 1 second but quickly got worse. I'm sure that by filing the silver off of these contacts they are just getting dirty fast.They are thinner and the contact area is no longer perfectly flat causing them to arc.   I'm thinking this might be it.

Mike
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radardoug

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Re: Studer A80 Mark IV Slowing down
« Reply #7 on: April 02, 2017, 08:32:40 pm »

Where is that LY4 contactor? Is that the braking circuit one?
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Mikeyod

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Re: Studer A80 Mark IV Slowing down
« Reply #8 on: April 06, 2017, 07:08:13 pm »

Yeah, that's the one. It looks like in the schematic it supplies brake current in one direction(Power amp, Direction logic, End of tape brake amp, Brake amp) and drive current( on the schematic it shows F-M1 I thought feed motor 1) in the normal position. Unless I'm not seeing it correctly which could be. A poor connection in the normal position could cause instability?
  Since I changed it. It went four days without slowing down. Today however, it slowed down momentarily sped back up to nominal and then no further trouble. That would be a pain if this were a red herring. Or maybe only part of the problem.
    RadarDoug do you say this could have no bearing on the slowing down ?

Mike
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radardoug

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Re: Studer A80 Mark IV Slowing down
« Reply #9 on: April 07, 2017, 01:30:21 am »

Didn't you say your tensions were good when youhad the slowdown? This being the case, I dont think the contactor is involved, as it is on the two spooling motors. Which means the problem is in the capstan circuitry.
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Mikeyod

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Re: Studer A80 Mark IV Slowing down
« Reply #10 on: April 07, 2017, 08:55:58 am »

That is true. But, I had to lower the tension by rotating the left hand tape tension sensor which also controls the reel motor current. Also, pressing stop the 1600 Hz would immediately return.
  I'm just trying to go through this logically because there are so many things on these machines that interact. I've changed all the ICs on capstan control card .372 because they are socketed and I had some, no change. All motors rebuilt by Athan corp. No change. Cleaned contactor, good for two days new contactor good for four days with only one slowdown. So if the contactor has nothing to do with it this is one pesky problem.
      Are there any other suggestions as to what it could be. That one slowdown shows there is still something. Could the RCA411  be the problem ? I would think that transistor either works or it doesn't ? Any help very appreciated !

Mike
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radardoug

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Re: Studer A80 Mark IV Slowing down
« Reply #11 on: April 07, 2017, 04:34:30 pm »

It looks like you have a similar problem to my machine. Note that the fact that when you press stop and get 1600Hz immediately is because the load comes off the capstan and the drive circuit can supply. I am suspecting either the output transistor or the drive transistor. The owner has a spare motor, and I am going to set the whole lot up on the  bench so I can work on it. Its too hard to do it on the machine.
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Mikeyod

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Re: Studer A80 Mark IV Slowing down
« Reply #12 on: April 07, 2017, 06:32:46 pm »

I guess that would be the BC140 on the capstan control card and the RCA411 on the back of the machine ? Do you have any part numbers for suitable replacements ? Maybe for the BC140 a 2N3107. A 411 replacement seems a bit more difficult.
   Let me know what you find !

Thanks,

Mike
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radardoug

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Re: Studer A80 Mark IV Slowing down
« Reply #13 on: April 07, 2017, 07:32:10 pm »

I'm a big fan of transistors used for vertical deflection in televisions, because they are made for high voltage and spiky conditions. I used to use these to replace MDA transistors in Ampex MM1200s. BUV numbers I think? Have a look through whats available from Mouser etc. Go higher in current and voltage and you cant go too wrong.
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Mikeyod

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Re: Studer A80 Mark IV Slowing down
« Reply #14 on: April 11, 2017, 04:21:53 pm »

Hi Doug,
Any discoveries with the bench testing ?
Looks like the BUV23 should be a good replacement for the RCA411

Mike
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