Tape slowing down Otari MX-5050 Bii

[timshel0]

Hello,

I am working on an Otari MX-5050 Bii and wanted to get some input from folks smarter than me. 

The first symptom was a screeching sound on the transport when the tape wind was greater on the supply vs take or vice versa. I spent some time rigorously cleaning  the entire tape path. This did make a pretty big difference. The screeching is gone and the tapes were FF/RWD.

We have transferred a few tapes since then. Now the tapes will cause the motors to stop in FF/RWD. 

As a troubleshooting step, when I run the tape directly from Supply reel to Take up reel (bypassing the transport), the machine (bii) can FF/RWD.

As a troubleshooting step I tested the tapes out on a 2nd Otari MX5050 (MKIV) and the tapes FF/RWD with no issues.

My initial diagnosis was old sticky tape. We are aware of SSS, loss of lube, binder issues, etc etc. We also bake each tape before putting them onto the reel. But now I am confused as to why one tape machine would be able to move the tape and not the other.

Questions
1-Is there a way to check if the supply/takeup motors are applying  the  torque?
2-Is the torque of the supply/takeup motors fixed during FF/RWD/PLAY?
3-Should we just accept that this machine is not able to work with certain tapes?

Also--if anyone needs the documentation for the Otari MX-5050 bii I have collected all the .pdfs the internet has to offer.

Thanks!

 

[Michael Tibes]

You could upload the manuals to the technical documents section.

1-Is there a way to check if the supply/takeup motors are applying  the  torque?

There are ways using spring scales. For example Studer explained it in their manuals. The 5050 might be too unsophisticated for detailed specifiactions in the manual, but maybe you get lucky?

3-Should we just accept that this machine is not able to work with certain tapes?

No, not if the tape is ok. The machine was a workhorse, it should work with any tape.

I currently have a 5050 with a broken reel motor in my workshop, but that problem seems very rare. This motor is really stuck, it doesn't turn at all by itself.

Did you try a new tape?

Michael

 

[Bo Deadly]

Try asking here:

http://www.tapeheads.net/forumdisplay.php?f=4

I don't know anything about Otari but on my ReVox reel motor tension depends entirely on AC applied through triacs that couple different windings of the PT (and there's a "reel size" switch but it doesn't really matter as much as you might think).

Just as a test, remove the reels, leave the hubs on and try FF and RW and use your hand to feel the resistance. They should spin (takeup CCW in FF and supply CW in RW) with decent force but if you really grab one tightly, it will of course stop. But there should be some decent force. If it does have good force, I would focus on the tape path. Tape guides could be a little off because something is bent or a spacer is wrong. Lay it down flat and look at it closely with magnification + light. Use your phone to make a video and look at it full-size on the computer. The edges of the tape should be clear and there should be very little to no shedding.

If the force is weak, it could be motors but motors and transformers are pretty tough so I would be more inclined to look at the power supply and particularly any silicon parts that are handling a lot of current like triacs and rectifiers.

 

[JW]

Yeah, the tapeheads forum is a pretty great place.

I wonder if the capstan motor could perhaps be causing these issues? It does need to be lubed and it's probably routine maintenance at this point to replace capacitors on the capstan servo board.

 

[radardoug]

The problem described is sticky shed. The screeching is a big giveaway. You are working with old tape? Ampex? You need to bake the tapes before transferring.  Note that Ampex in particular releases a very sticky clear goop, which is hard to see on heads and guides, and even harder to clean off. I presume you are cleaning every element in the tape path?

 

[Michael Tibes]

Back in the day there were charges of Ampex tapes that already came sticky from the factory. It even turned into a worldwide shortage of tape for a little while. I'm not sure if baking can cure such tapes 100%. So unless you work with a proven ok tape, you might be trying to fix the machine while the tape is the culprit. All the effects you describe fit the bill for sticky tape...

Michael

 

[timshel0]

Hey thank you all for the replies!

I did use a new MRL tape as a control. The MRL tape FF/RWD with no issue.

The tapes we are transferring are slowing down on the 5050 bii.

The tapes we are transferring do not slow down on the 5050 MKIV.

I initially decided it was sticky tape causing the slow down until it played on our 2nd machine. And Yes! I did bake the tapes (for longer than usual) and clean the the entire tape path heavily. 

Ah! Yes I am familiar with the Studer machines too. What I can do is measure the torque using a spring scale on the MKIV and then compare that to the Bii. I will also try out the hands-on resistance method. At least I can try to rule out the motors.

I am pretty sure I checked the voltages going to the motor and they were okay. Otari supplied a sheet that tells you the timing of each mode and the voltage applied to the motors. At least that is how I am reading it. Attached to the post.

The Capstan would make sense if I had speed or pitch issues, but it does not interact with the transport when using FF/RWD.  During my maintenance I did lube the capstan with iso vg 32 oil.

So I will investigate the tape paths per squarewave's suggestion. Test the torque with scales and by hand.

 

[Bo Deadly]

Does the 5050 have motor run / start caps?

 

[radardoug]

So the MRL tape works fine, and THE TAPES YOU ARE TRANSFERRING dont work.
The clue is right there!
Dont worry about your machine, worry about your tape. If you have another machine that doesn't have the problem, then use that.

 

[Gold]

I agree it’s sticky tapes. Sticky tape moves much better over roller guides than fixed guides. The fixed tension guides on a 5050 are terrible for this.

Look at Studer  A80 or A820 you won’t see any fixed guides. All rollers. That’s what you want.

 

[Tubetec]

Im not sure if its an issue with MX5050 ,but the old MTR90 would sometimes have capstan slippage relative to the tape , it led to all kinds of jerky uncontrolled movements particularly during speed up /slow down , it could be compounding your issues .
Always start slowly on ff or rew until you know the condition of the tape is good ,if theres an ugly  chattering sound  hit stop straight away.

 

[radardoug]

No, the two machines are completely different. The MTR90 is servo controlled. The 5050 is similar to Ampexes such as 300,350,440. The OPs problem is he is transferring some sticky shed tapes.

 

[Gold]

An Otari  MTR-10 or MTR-12 would be a decent machine for this. They have mostly roller guides.

Otari never made a two track servo controlled machine like the MTR-90. Even the lower priced MX series multitracks used a traditional capstan and pinch roller arraignment.

 

[Tubetec]

I was confusing it with  the MX-80  which also seems to use the older capstan/pinch type arrangement.

 

[timshel0]

Hey folks I am going on vacation so I will not be able to get to these machines for a week or two. Thanks for all the replies so far!

 

[plimousse]

Hi,
On MX5050, the pinch roller capstan is drive by a solenoid, with spring.
You must check if you have two time , First the solenoid is energized, and the spring "retain" the pinch roller,
After the pinch roller stick gently on the tape...
Please let me know if this help you?
Cheers,
Pascal