Studer A80 left roller guide

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I have now received my A80R from Holland. Everything seems working, tapes tension is correct, and except some noisy bearings that I must replace there is little to complain. Just two details are bothering me. When I press the stop machine everything stops fast and smoothly except the left roller guide (usually hidden by the headblock cover) that keeps rolling for a few seconds until the tape pressure stops - is this normal?
Also the capstan is polished in the contact area - will it affect performance? Must of the photos I seen in the net have the same polishing.
Thanks for your advise and help.
Francisco

[Ki Choi]

Hi Francisco:

To answer your first question, the Tape Guide Roller has a relatively heavy flywheel on the bottom of its shaft to keep its speed constant.  However, the friction from the supply side tape tension should stop the roller immediately going from Play to Stop and even after FF/REW modes.  As you take the covers off of your tape transport, I would also check to make sure the positions of the L & R dashpots linked to the tension assemblies are in their correct locations (out of three possible positions).  It took many hair pulling hours on one of my A80RC Mk IIs to solve an odd tension problem that turned out to be - the studio where I had acquired the machine had the A80 setup for 1/2" tape at one time with the dashpots in the wrong positions and forgot to change it back to 1/4" tape setting.  In order to confirm the correct tension setting, you would need to use the Tenelometer (60g -70g from top of my head) but if it is not correct, you will first see the loops developing in the tape path when going from Stop to Play or Play to Stop, etc.  Thus, even though your assessement of the tape tension being correct, I would suggest, you double check it.  It's an easier problem considering the alterntive of frozen guide roller...

In regards to your second question of the polished capstan...  I have mixed feelings about the situation.  It is true when the Studer capstan shaft was new, it had matte finish from the top to bottom and as time went on it eventually became mirror finished.  There are Studer experts who would advise the mirror finished capstan is never good.  On the other hand, when I brought home one of my Nagra T Audio's, I was surprised to see the capstans (yes two..) were mirror finished from top to bottom with no difference for the tape contact area.  The second Nagra T Audio had the same polished capstans... Maybe Doc B can chime in with his take.  Therefore, if you think the tape is slipping due to the polished capstan, you can send it to Athen's for their sand blasting...otherwise enjoy!

Ki

[Tim]

Polished capstan shafts started showing up on Revox B77s a few years after they first came out.  They exhibited abnormally high amounts of wow/flutter due to this.  You should have a repair shop carefully measure your "new" deck's wow/flutter and see if it's within published Studer specs.  It's important that they uses a W/F meter that has the proper weighting curve and proper flutter standard (the same w/f standard that Studer uses) .  The W/F should be measured in the play mode with a pre-recorded speed tape (MRL) and also be checked at the beginning and end of a full reel of tape.  Like Ki Choi mentioned, if it's out of the W/F spec, you can have the shaft sand-blasted.

[Ki Choi]

Hi Tim:

Very good point.  Having the W/F measurement compared to the Studer spec with the capstan would remove all subjective opinions.

Here's the link for Francisco if he wishes to rebuild the capstan motor:

http://www.athan.com/cgi-local/store.cgi?sid=74175209&product=1418

Ki
PS: corrected link.

[microstrip]

Hi Ki and Tim,
Thanks for your advice. I looked at the dash pot of the left tension arm and it seems loose - the right one is much more damped. Do you know if it can be refilled? I have access to  silicones of different viscosity.
Concerning the capstan shaft I have a doubt - the motor seems perfect and the weight makes impractical sending it from Europe to the US and back. Can I send only the shaft? JMTechnical Arts can resurface it and I also found that MDI can sleeve the capstan with a ceramic coating. 
BTW I checked the capstan shaft with a Mahr 40F micrometer  - concentricity is really better than .5 micron!
   

[Ki Choi]

Hi Francisco:

Let us know the version of A80 you have.  There were older version A80 transport that used oil filled dashpots and later Studer upgraded them to the silicon grease filled kind.  I don't think you can refill the leaked out silicon grease.  Studer referred to the grease as "special" and I couldn't find any othe details.

A good thing about the A80s is that you will find people parting out the decks and selling the dashpots.  Make sure you get one from a A80RC Mk II or A80VU Mk II to be sure that they are silicon grease filled dashpots.

On the other hand, unless someone had disassemble the dashpot assembly before it got to you, the grease may not have leaked out.  The section 2.4.3 of the A80RC Mk II manual explains the tension adjustment very well.  Before you disassemble or try to replace the dashpot, make certain the rest of the tension assembly is working properly. 

Did you compare the position of the supply side dashpot assembly in comparision to the right side?  They should be mounted in mirror image.

Ki

[microstrip]

My machine is an A80R - the first model. I see now that one of the damping pots is an original and the second one is from a A80RC mk2 - perhaps this explains the difference.
However this is the kind of part is it is risky to buy from broken decks - how can we be sure they are in good conditions? I will try to refill and balance them to be symmetrical. I have successfully repaired several tonearm lift dampers using a special silicone fluid that was used to couple photomultipliers to scintillators.   
The strange left roller  guide behavior only shows when pressing play or stop in fast forward mode - I can go from fast forward  to rewind on any mode from rewind smoothly. There are no tape loops in any case.

Looking at the capstan I found the shaft still has 9.5 mm in the upper part that are mint and decided to try a little experiment -
using larger screws I will fit a 7 mm precision spacer between the motor and the chassis. Like this the tape and pinch roller will work against a matte shaft.   

[High and Outside]

Looking at the capstan I found the shaft still has 9.5 mm in the upper part that are mint and decided to try a little experiment -
using larger screws I will fit a 7 mm precision spacer between the motor and the chassis. Like this the tape and pinch roller will work against a matte shaft.   

Be quite careful when doing this experiment. The perpendicularity of the capstan is a critical element in the tape path.