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Universal Capstan Motor

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  #21  
Old 11-23-2016, 08:18 AM
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mrdbdigital mrdbdigital is offline
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Terry,

Here's a thread on refinishing the capstan with sandpaper:

http://www.tapeheads.net/showthread....ight=sandpaper

Dave __ (Yep, that Dave)
  #22  
Old 11-23-2016, 02:39 PM
eddisc eddisc is offline
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IF the pinch roller isn't making full contact with the capstan, re-texturing the capstan won't help... Cornel may be on the correct path. Also - the draw/hold voltages to the PR solenoid s/b checked.
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  #23  
Old 11-23-2016, 05:46 PM
tpir72 tpir72 is offline
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Thank you, I will check both. Is there also a pressure/tension adjustment in the mechanics of that roller/arm?

Do you happen to know if there is a voltage adjustment for that specific board?

Maybe the overall power supply needs a slight tweak?

The outlet machine voltage is 122.6 volts AC so the source (wall outlet) isn't low.


Happy ThanksGiving!

Terry
  #24  
Old 11-23-2016, 10:20 PM
cornel cornel is offline
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Yes , there is an adjustment - mechanical- for pressure roller. I would not recomand to change it , if is original sealed. But use a solvent and a brush for removing the dried grease on the articulated levers coming from solenoid plunger and then re-lube .
I had the same symptom long time ago , after one year of not using the reel to reel.
Also , pay attention on friction between pressure roller an its own shaft . Are there two spacers , but different thickness , one below , one above , if put in reverse , when you secure the pressure roller black metallic lid , you tend to increase friction on pressure roller. So screw for securing just a little bit meantime rolling the pressure roller with your fingers for sensing when is not free spinning anymore. It must remain free spinning in the end. Before that , clean with solvent the old black residue existing on the shaft and on the upper and lower metalic body of roller and drop just a tinny drop of oil for sewing machines.
  #25  
Old 11-24-2016, 09:49 PM
tpir72 tpir72 is offline
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I honestly don't see lube on anything related to the pinch roller, arms or solenoid shaft.

I tried to get a couple of really tight photos of the pinch roller and capstan shaft but the camera won't focus that tight. The one photo attached makes it look a lot dirtier than it really is.

Before I lube the wrong part or rough up anything with sandpaper or worst case tighten the nut slightly at the end of the solenoid arm I wanted to send these photos for comment, please.


Thanks again for the help.

I sincerely appreciate it.

Terry
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  #26  
Old 11-25-2016, 01:10 PM
JVRaines JVRaines is offline
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Maybe the solenoid spring needs tightening. Put a loop of string around the pinch roller shaft and hook it up to a 3 kg spring scale. Put the deck in EDIT-PLAY and slowly pull the spring/string up in a line with the capstan and see what the scale reads when the roller just loses contact. It should be 2.5 to 2.7 kg. There's a nut below the solenoid spring that adjusts its compression.
  #27  
Old 11-25-2016, 09:48 PM
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Antonis Antonis is offline
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Out of the blue I had something similar happening to my Revox. Turned out it was the shim between the the pinch roller and pinch roller cap which was a just a tiny bit deformed from last time I removed the pinch roller and caused speed drops. You have one of those as I see in illustration 4-3 on the bottom of page 4-4 of your SM.
Before you try anything as difficult as adjusting your pinch roller pressure torque could you please remove this shim and see if this corrects the problem?
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Last edited by Antonis; 11-25-2016 at 09:51 PM.
  #28  
Old 11-25-2016, 10:02 PM
tpir72 tpir72 is offline
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Thanks, I will try that first. I also noticed that as part of the pinch roller assembly, under the "Cue" lever is something that looks like a cheap cabinet latch. One screw was loose in it making one side slightly higher and stopping complete travel of the arm.

I lowered that down and tightened but still didn't make enough difference to have the pinch roller engage with the correct tension. Thought for sure that was the issue. Still runs slow without keeping a finger on the roller cap while the tape plays.

Very frustrating...
  #29  
Old 11-25-2016, 10:19 PM
cornel cornel is offline
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Photos taken are excelent.
There are two nuts on the rod going from solenoid toward the pinch roller arm. One is for adjusting , other for blocking. Those are for setting position- pressure- when engaged in some limit. If factory sealed , I would not recommend to change the setting.
There is the metallic sleeve flange on solenoid having two cut out egg-shaped wholes.
This is for adjusting solenoid force on beginning of actuating. Again , if possible , do not change the setting if factory sealed.
Remove the pinch roller and try to see if mechanism is softly moving when pushing the plunger of solenoid by hand. On mine , the grease on springs- I noticed lack of grease on yours- and on edge of transmitting rod was dried. Not knowing the history of mine , is possible that yours to look exactly as it should.
But I noticed one major difference between the black metallic lid on the pinch roller ! Mine is considerably thick- probably two times - compared with yours and has some thin factory made circles engraved on it. Are you sure your pinch roller lid is original ? Because on the opposite side- the one getting contact with the rubber roller face- the lid has some particularly shape , in order for one spacer to fit exactly for fixing the roller on its shaft but without friction between roller hub and internal face of the metallic lid.
Also , for me , it seems your pinch roller is dirty and so the capstan shaft.
Please try first to clean more intensively those two , see if the rubber is not dried , use some sand paper to remove one mm of ruber if dried.
You can use sand paper for redo the original porosity of capstan shaft , but be very careful not to exagerate.
  #30  
Old 11-26-2016, 02:53 AM
gustavoa gustavoa is offline
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Hi,

Sometimes with time the pinch roller dries up and shrinks. Consider ordering a re-furbished pinch roller by Terry, from Terry's Rollers.
He offers an option where you can ask for a pinch roller with a little bit more of material or a bigger rubber circumference. Send him a note and ask him about it. It is an option to consider before messing with factory adjustments.
  #31  
Old 11-26-2016, 10:28 AM
JVRaines JVRaines is offline
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If you remove material from the roller or buy new rubber from Terry, you will still need to check and possibly adjust the roller pressure. All you need is a spring scale ($12 at Amazon), a piece of string and a wrench. Taking 10 minutes to check the existing roller pressure will at least enable you to identify or rule it out as the cause of the problem.
  #32  
Old 11-26-2016, 07:42 PM
tpir72 tpir72 is offline
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That's a great resource! Thank you very much, so if I go for a new roller or send mine to be refurbished, should I have him add .015 or .050 to the original factory spec?

I'm OK if it runs slightly fast provided the speed is consistent. I can fix the recording speed in Audicity.


Thanks for the help.

Regards,

Terry
  #33  
Old 11-26-2016, 08:07 PM
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tapetech tapetech is offline
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Quote:
Originally Posted by tpir72 View Post

should I have him add .015 or .050 to the original factory spec?


I'm OK if it runs slightly fast provided the speed is consistent. I can fix the recording speed in Audicity.

If recovering the roller at Terry's, you get the standard size. He has that on file.

Why are you assuming the deck would run fast? Pinch roller diameter does not effect tape speed. If the deck runs fast for any reason, you adjust the capstan motor for the correct tape speed using a speed tape and counter. You don't "fix it" in your computer. Why would you do that?

Whether you have the original pinch roller, a sanded original pinch roller, a new recovered roller or just a new roller, the pinch roller pressure has to to be adjusted if it is not correct. Is it correct to spec? You should also know that low pinch pressure can be caused by the pinch solenoid not fully bottoming the plunger. Does the plunger always bottom? You need to know that.

Also, you changed the symptoms on us. First you said that the speed was good, but would briefly dip and come back up. That can only be caused by an intermitent reduction of voltage to the capstan motor which is why I and others told you to check all motor related switches, pots, connectors.

Then later you said the deck was "running slow". That is quite different. That can be caused by one , some or all of these: low pinch roller pressure, bad pinch roller rubber, polished capstan shaft, capstan bearing worn or in need of lube, a mis-adjusted voltage to the capstan motor (speed adjust).
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Last edited by tapetech; 11-26-2016 at 08:15 PM.
  #34  
Old 11-26-2016, 08:10 PM
BruceD BruceD is online now
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@tpir72'

The diameter of the pinch roller has no influence on the tape speed. That is determined by the speed and circumference of the capstan. The pinch roller merely creates the "friction" to advance the tape at a constant speed.

*** edit

Ah, tapetech got in there ahead of me.

Last edited by BruceD; 11-26-2016 at 08:17 PM.
  #35  
Old 11-26-2016, 09:03 PM
tpir72 tpir72 is offline
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Sorry Tapetech,
Just trying to give feedback as I observe things. No intent to change anything when communicating here. What I know is the deck will play normally and I am experiencing more and more speed dips without rhyme or reason.
As I mentioned before, quite by accident, I put a little downward pressure on the pinch roller during a slow-down moment expecting the speed to dip even lower and instead, the speed corrected itself up to normal until I released pressure.
I don't see any dried lube to be replaced and with the exception of one loose screw on this odd cabinet latch under the "Cue" lever, everything looks visually where the factory set things. There is orange stripping marked on some assemblies.
I was able to run off three full tapes last night by keeping constant downward pressure on the pinch roller arm.
All I trying to understand is if everyone here believes spending $85 will fix the issue or if I should buy a scale that measures grams to check the tension on the arm first... Or if I should try to adjust the spring/screw on the roller. I don't know what the propper solenoid voltage should be and do I meter it in or out of the circuit?

Again, I'm sorry if I don't know all the propper terminology, I've owned two reel-to-reel decks in my life. A Radio Shack Quadrophonic deck in the late 70's and this beautiful Otari. This is my first need or attempt to troubleshoot the deck as it has worked flawlessly until recently with the speed issue.

Regards,

Terry
  #36  
Old 11-26-2016, 09:39 PM
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tapetech tapetech is offline
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1 Does the pinch roller spin freely?

2 Does the pinch roller move up and down freely by hand? If you move it to the capstan, does it return to rest instantly and freely?

3 If you put deck into play with no tape, it should be very difficult to stop the pinch roller by hand. Is it?

4 Is the solenoid plunger bottoming? Put deck in play and push hard on the plunger with a screw driver tip to see if it is fully bottomed into the solenoid.

-You can't see dried lube. Lube is inside of bearings.

-No one said to check the solenoid voltage at this point of trouble shooting. Nothing yet indicates it may be low.
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  #37  
Old 11-28-2016, 08:57 PM
tpir72 tpir72 is offline
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1 Does the pinch roller spin freely? Yes, using my index finger and spinning the roller, I might get 2-3 full rotations with one hard swipe. I don't feel any dryness or scrapping when I turn it slowly.

2 Does the pinch roller move up and down freely by hand? If you move it to the capstan, does it return to rest instantly and freely? Yes, right back to it's original starting point without delay.

3 If you put deck into play with no tape, it should be very difficult to stop the pinch roller by hand. Is it?It is, I put so much pressure on it, it was starting to burn a black stripe in my finger. I would have had to have put a ton of pressure to stop it turning to the point of breaking something.

4 Is the solenoid plunger bottoming? Put deck in play and push hard on the plunger with a screw driver tip to see if it is fully bottomed into the solenoid. Yes, it is bottoming out at the plunger.

I'm still trying to understand why when I force more downward pressure on the pinch roller the tape speeds back up to normal. Could it be as simple as adding a quarter or half turn to the adjustment nuts?

Regards,

Terry
  #38  
Old 11-29-2016, 08:30 AM
JVRaines JVRaines is offline
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Pardon, but this is all getting a bit silly. Why not just tighten the spring and see what happens? It's a nut and a coil spring, not a human brain. Buy or borrow a spring scale and you can set it to factory spec of 2.52.7 kg.
  #39  
Old 11-29-2016, 10:45 AM
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Quote:
I'm still trying to understand why when I force more downward pressure on the pinch roller the tape speeds back up to normal. Could it be as simple as adding a quarter or half turn to the adjustment nuts?
Sounds like you already have close the correct pinch pressure if it is very difficult to stop the roller by hand as you say.

A polished capstan surface could easily explain why the speed is slow yet you have good PR pressure. It is a common defect in the Otari decks and it can be easily repaired. Is the capstan polished? (not looking mat) Photo?
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  #40  
Old 11-30-2016, 12:21 AM
tpir72 tpir72 is offline
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Please see the attached photo of the Capstan shaft. Not a great photo but it is as close as the iPhone 6 would focus.

To the touch it is really smooth.

What is the fix if it is too smooth? I read somewhere that 400 grit sandpaper might be an option but isn't it just going to polish it further than roughing it up?
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