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Universal Capstan Motor

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  #1  
Old 11-15-2016, 11:44 PM
tpir72 tpir72 is offline
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Otari MX5050 Variable Speed Problem?

Hi Everyone,
I have a pristine Otari MX5050 with only 100 hours on it. The unit has been working great until this past week. When playing back any 15ips tape there are random speed dips that make the pass unusable. The speed dips don't happen in the same places each time the tape is run on the machine. The effect is if you randomly put your thumb on the reel while playing. The duration only lasts a fraction of a second, multiple times per minute.

I have tried staring at the reels to see if I could visually see the moment of slowdown. I can't.

After the problem started, I cleaned the deck within an inch of its life. Lubed the capstan. I have a new belt set coming over from Germany.

I'm stumped on why this is happening and how to fix it.

I downloaded the full-service manual but don't have some of the devices or experience to try to calibrate the deck or troubleshoot with a scope.

I have a set of tapes loaned to me that should be finished and shipped back to the owner.

I don't cash to send all the tapes to a special recovery studio.

Any help, advice or observations would be sincerely appreciated.

Regards,

Terry
  #2  
Old 11-16-2016, 12:11 AM
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tapetech tapetech is offline
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Clean the speed hi/low switch on the back circuit board.
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  #3  
Old 11-16-2016, 12:22 AM
tpir72 tpir72 is offline
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Thank you very much.

Do I need to pull the circuit board to get to the switch? Is the switch obvious/marked?

Regards,

Terry
  #4  
Old 11-16-2016, 01:22 AM
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tapetech tapetech is offline
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No need to remove the board. It swings down on a pivot. Don't know if it is marked, but you can read about it in the owner's manual or service manual. It converts the deck from a high speed deck to a low speed deck.
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  #5  
Old 11-16-2016, 10:07 AM
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Tinman Tinman is offline
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Just one sec.....

WHICH 5050 do you have? The only one that uses belts is the first version which has an AC synchronous motor and no vari speed control.
That machine is very simple and should not behave like that.

The later decks used an electronic speed controlled motor and have no belts.
These decks tend to suffer from oxydized switches, but sometimes the capstan motor itself can be trouble.

HOWEVER..... (!!!)
You are digitizing someone elses tapes. Are you SURE that none are getting sticky, which can make them catch on the guides and do exactly that?
Do he guides move or wiggle as it plays? On a good tape, they should not.
On a failing tape, the guides will bounce around.
  #6  
Old 11-17-2016, 01:14 AM
tpir72 tpir72 is offline
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No Change

Hi,
Found the large hi/lo switch on the circuit board and cycled it a bunch of times. Used lubricating contact cleaner, even tried to scrape any visible metal inside the switch.

Put it back together, same problem.

No sticky Shed Syndrome.

Kinda stumped on this one.

All tapes were stored tails out in a horizontal fashion.

No place to repair one in town.

Thoughts?
  #7  
Old 11-17-2016, 01:28 AM
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You can clean the on/off switch for the vari-speed pot. Clean the pot too.

Clean the pins of connector H (right next to hi/low switch). Do this by brushing on some contact cleaner to the pins.

You can unplug the wire harness going to the capstan drive board and clean those contacts.

The left brake could be intermittent. See the L brake solenoid moves at all when the speed drops.

See if any leaking capacitors on the back board or the capstan driver board.
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  #8  
Old 11-17-2016, 01:32 AM
cornel cornel is offline
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Did you try to push, just a little, the pressure roller against capstan shaft ?
Did you check if the pressure roller spins freely on its shaft when not engaged ?
  #9  
Old 11-21-2016, 07:22 PM
tpir72 tpir72 is offline
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SW1 Hi/Lo Switch?

Thank you gang for helping me with this darn speed issue. So I have decided to remove the switch and either put in a header block with two pin jumpers or simply cut off wire leads from resistors to use as jumpers(without the resistor).

I found a schematic from a site called AnalogRules. TapeHeads site won't allow me to upload it in this post due to a Security Token missing.

The slider switch is single throw (Hi/Low) but the contacts represent twelve soldered pins.

I was allowed to upload two photos of the switch.

I want to jumper it in High mode.

Does anyone know the pinout of this switch before I inadvertently destroy it while removing it with solider wick?

Could I please ask for a screen grab of this switch on the schematic?

Thank you very much for the help.

Regards,

Terry
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  #10  
Old 11-21-2016, 07:24 PM
tpir72 tpir72 is offline
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I should also mention that there are an additional four soldered mounting pins/post on the four corners of the switch. I'll assume they are not a shield but just mounting....
  #11  
Old 11-21-2016, 07:45 PM
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tapetech tapetech is offline
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Why do you think the switch is defective? There are dozens of things that can cause the speed to momentarily slow down in the deck.

Measure the switch contact resistance with an ohm meter. Should be less than .5 ohm resistance.

If you just want to bypass the switch, you don't have to remove it. Just solder wire jumpers to the board where the contacts are normally close.
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  #12  
Old 11-21-2016, 08:27 PM
JVRaines JVRaines is online now
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Only 100 hours but how old is this Otari? Could it be in need of other transport lubrication besides the capstan bushing?
  #13  
Old 11-21-2016, 10:18 PM
eddisc eddisc is offline
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NO mention yet of the speed select switch on the front?!?!? someone's slipping

Tails out IS good - but Hz storage?? Not so much!! Store like Lp's - vert!!!
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Last edited by eddisc; 11-21-2016 at 10:21 PM.
  #14  
Old 11-21-2016, 11:23 PM
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tapetech tapetech is offline
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Yes, like he said, clean the front panel speed select switch as well! These Otari's are quite infamous for dirty switches throughout the deck. Also the record and mute relays sometimes cause problems (not your speed problem).
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Last edited by tapetech; 11-21-2016 at 11:49 PM.
  #15  
Old 11-22-2016, 07:50 PM
tpir72 tpir72 is offline
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Extra Fine Sand Paper?

Hi Gang,
I saw mention somewhere about using super fine sandpaper on either the capstan shaft or pinch roller.

The capstan shaft is slick as a baby's bottom. The pinch roller rubber isn't hard or brittle, still very pliable to the touch.

I'm having a tough time finding the sandpaper trick again. Do you recommend doing it to the capstan or pinch roller?

Regards,

Terry
  #16  
Old 11-22-2016, 07:52 PM
tpir72 tpir72 is offline
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Also can't find any reference to other lube points in the manual beyond the capstan.

What other recommended lube points on the MX5050?
  #17  
Old 11-22-2016, 09:25 PM
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A momentary drop in speed would not be caused by a defect (polished) capstan surface or a bad pinch roller or by anything that needed lubrication.
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Tim@MusicTechnology.com**** WWW.MusicTechnology.com
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  #18  
Old 11-23-2016, 12:56 AM
tpir72 tpir72 is offline
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Problem Found - Need Help with a solution please...

Problem Found- Need Help with a solution please...

While a tape was playing slow, I applied horizontal pressure to the rubber guide wheel that presses against the capstan shaft.

With a lot of pressure, the tape played normally, when I backed off on the pressure the tape slowed to below normal speed. No other speed adjustments have been tweaked including the pitch control.

What would be a good solution to this?

Regards,

Terry
  #19  
Old 11-23-2016, 03:32 AM
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keithatrochdale keithatrochdale is offline
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With age sometimes grease hardens and this often stops the pinch wheel pressing fully on the capstan.

The solution is easy, clean off the old grease and replace it.

I have a tube of lithium grease I got from Halfords (bike and car accessories). store.

.
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  #20  
Old 11-23-2016, 07:55 AM
cornel cornel is offline
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In order to increase pressure of pressure roller on capstan shaft , please check and clean the dried grease on pressure roller mechanism connected with its electromagnet - on back central position of Otari.
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