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Author Topic: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.  (Read 10950 times)

Offline YoAdrian

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Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« on: August 10, 2014, 05:47:05 PM »
I am so Happy I found this Forum. Thanks for creating such a place.

I've had this Otari MX5050 Biii-2 for a Week. Free, from a friend. This is my first RTR. My issue is, it will not Rewind or FastForward with tape in the Tape Transport. It will move for a few seconds then stop. I can give the reels a push and they move a bit but will remain stuck. I have 7 inch reels so I did select Small reel on the supply and take up button.  If I hook up the tape up directly, supply reel to take up reel, bypassing the Tape Transport, it works fine. I read the Otari Manual page (140 Troubleshooting Tape Transport) It says the below.



I only have one tape. The tape I have does seem very sticky, first play through it got the capstan very dirty. The capstan was shiny and chrome, after running the tape through once on one side, the capstan, and other parts were dirty. Maybe the tape suffers SSS.

Things I checked:
1. Rewinds and Fastforwards without tape
2. Ensured Brakes are not engaged during Rew and FFW
3. Ensured Tape Transport was clean
4. Made sure Reel Motor not seized
5. Disabled brake by pressing brake plunger The reels move freely
6. Undid and reseated all connectors.

When the tape was hooked up directly from Supply to Take up reel bypassing the tape transport, it did finish within the time indicated in the Otari Manual. Since we run 60Hz in USA it should fast forward 2500 feet in 90 seconds. The reel I have is 1200 feet and it was able to fast forward in 35 seconds. This of course is bypassing the tape transport.



The other portion of the troubleshooting says try another tape on the machine. I don't have a second tape. I will be getting a second Tape sometime this week. Hopefully it isn't sticky too.

If you could offer anything I haven't thought of. I tried to do the obvious. I did think it may be the 6uf capacitors in the control board for the reels or maybe the relays. But then play wouldn't work right? I got the schematics from someone on this forum last night. Bob Schneider, Thanks Bob. They were posted on his website. I will take a look at them along with your further guidance. I am stuck at the moment. The machine plays fine, so play and flip at this moment.

Regards,
Adrian Magana

Offline docb

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #1 on: August 10, 2014, 10:14:52 PM »
If you haven't yet, try leaving the deck on overnight. If it is a cap issue that can sometimes help them to reform and take a charge.

Also, try helping the the reels as they start spinning during that first few seconds, before it stops. Otaris can struggle a bit to get up to speed if they haven't been used in a while.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline YoAdrian

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #2 on: August 11, 2014, 06:38:10 AM »
Doc,

     One thing I noticed. When I press rewind or fastforward the motors seem to get very tense. As if they are opposing each other. When they are stuck I can press Edit I can hear what sounds like a relay actuate inside and causes the reels jitter a bit. They don't spin just kinda jerk a bit. I uplugged the cable going to the motor that takes care of FFWD (reel on the right, take up reel) The reel has no power and I can rewind really good with the tape in transport. And vice versa, I unplug the motor that takes care of rewind and I can fast forward.

     Something is not disengaging when I press FFWD or REW. I wonder why the CUE button makes the motors jump while stuck in rewind or ffw. I will look at the cuircuit board that controls the Motors. I suspected these two diodes that are next to the relays when I first started. But they seem to take care of Small and Large reel selection. I took them out of the circuit and they tested fine.

     I will look a the schematics in that section to see what else it could be. I don't have a spare board to test my findings so I will have to test components and find a cross reference for them. I was looking at one of the diodes and couldn't find it online. I think the number on the diode may be a Otari part and not a general designator number like the common 1N4001. Thd diode I tested said 0256. I couldn't find a diode like that one online.

     Can you let me know what else to look for? Below is the schematic for the board I suspect. Thanks for your help, typing things out helps me think. I was able to take care of all the other issues the Otari had. They were all related to gunked up old dried up grease. Everything moves smooth now. Well, not ffw or rew.



Regards,
Adrian Magana

Offline ironbut

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #3 on: August 11, 2014, 12:58:13 PM »
If the machine will fast forward and rewind without a tape but won't when the tape is threaded, it's almost certainly the tape.
Before you get in there and change any adjustments, get yourself a new tape. I'm not talking about an old but unused tape. A new RMGI or ATR tape. Everyone should have one for testing their machine.
You should also clean the tape path thoroughly before using your new tape. There's probably a good bit of goo on there.

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Offline docb

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #4 on: August 11, 2014, 01:40:10 PM »
Yup, stay with the easy stuff first. If leaving it on overnight didn't change anything, try another tape.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline YoAdrian

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #5 on: August 13, 2014, 11:09:42 AM »
Doc/Ironbut,

     I did think of the easy stuff first. I don't have another tape to use/test with, this is my first RTR and I only have one 7" reel from ebay. I got a bit wordy in my previous post. Basically, it works in rewind and fast forward with tape in the tape transport if I unplug power from one of the reels.

     I took a look at the IC (IC31) that handles the actions of the play/rew/ffwd buttons. I noticed that if I left the tape in transport (when it gets stuck) while rew or ffwd. A signal called Traction Force is turned on while in ffwd or rew (IC 31 Pin 12) If I connect them reel to reel bypassing the tape transport it does not turn on the signal at (IC31 Pin 12) and the tape is able to rew and ffwd.

     Is there something that is sensing this? Like you guys said most likely a bad tape that is getting stuck in the tape transport. Is this machine able to sense that the tape is getting stuck? Still reasoning with when I unplug power from the right reel, I can rewind. The left reel is left connected. I was messing with the control board that controls the motors (power was off) and got a nice burn on my finger from touching a really hot 3 watt ceramic 100ohm resistor that overheated. The resistor overheated because I left the reels in the stuck mode in rewind. I would post a picture but it is on my middle finger.. wouldn't look good online.

     I have another tape coming in the mail this week, I will test with that one. I don't have the means right now to purchase a new tape like you mentioned. Thanks for your help guys, I have not given up on this and will continue to update until I figure it out. Just in case someone else has a similar problem, hopefully this can help.


Regards,
Adrian Magana

Offline ironbut

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #6 on: August 13, 2014, 12:14:35 PM »
With most reel to reels the capstan is what moves/controls the forward tape speed. That's the motor that has all the servo controls and is referenced to some sort of frequency generator.
Without power/brakes even motors on the supply and take up reel, the machine would still move the tape across the heads at a nice steady rate.
The sound would not be very good/consistent because there would be nothing to hold it against the heads (even with dual capstans the tape between them would get loose and loose contact).
You would also end up with a pile of tape at the right side of the machine (take-up).

Fixing these issues is the job of the reel motors.
They provide back tension to the tape.
If you Play the machine without a tape loaded, the reels will move in opposing directions.
Same goes for fast forward and rewind (except the one reel will spin a lot faster).

So, if your machine is stuck because of some sticky tape, relieving the tape of the back tension (usually around 50-100 grams per foot) would probably be enough to let the tape move.
One of the things that you look for in a quality machine design is "how gentle" it handles fragile tapes. This means it can't have much more torque than is absolutely necessary to move a normal tape across those heads perfectly.
That's why a good machine will freeze rather than snapping a priceless tape.
steve koto
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Offline YoAdrian

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #7 on: August 13, 2014, 12:52:38 PM »
You know,

     Now that you mention tension. I do notice that when the tape is threaded, and I hit play, the tension on the tape seem like a strangle hold. When the tape is stuck in the rew or ffwd mode I can pluck the tape and it sounds like super tight steel wire being plucked. Too tight, any more tension and it will certainly break the tape. Is there anywhere to change that tension?

     I notice there is a pinch roller tension adjustment but that doesn't seem to make sense because the tension is still there when the pinch roller disengages and is put into the rewind mode. I will keep digging through the schematics/manual to see if I can find such an adjustment.

     There is also a brake tension adjustment, the brakes disengage when in ffwd and rewind. So the tension is definitely coming from the motors.

Regards,
Adrian Magana

Offline ironbut

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #8 on: August 13, 2014, 01:04:17 PM »
There is no way to adjust tape tension on that particular machine.

I really wouldn't worry about anything till you replace that tape.
Of course there's a chance that it's not the the tape, but it's so likely that it is that doing anything before the new tape doesn't make sense (and could screw something else up).
steve koto
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Offline Listens2tubes

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #9 on: August 14, 2014, 09:36:34 PM »
On my BII models dirty switches are usually the main cause of problems. Try cleaning the Speed switches, on front and the main board as well as the Reel (Large-Small) switch, exercise the Pitch Control knob(in and out) and Monitor switches. That H - L switch on the main board controls more than just speed and can be the fix for some of the weirdest combination of maladies. Had a machine that a tech said the capstan motor was defective. Cleaned the H - L  switch and the capstan works fine. For that internal H-L switch you will need the main board swung down, then turn the machine on it's side, spray DeOxit into the side of the switch while working it.
Neal - Ampex Fineline F-44, 3 - Otari MX5050BII-2, Revox A77 Mk II , Teac A 4010s, 4070, Sony TC102A, Magnecord 1020, Systemdek IIX/Dynavector Karat 17D2MKII, CEC CD3300 CDP, K Works NanoMax DAC, Van Alsine Transcendence Eight+ tube preamp, Dynaco MkIV amp pair, Paradigm Reference Studio 100 v1

Offline YoAdrian

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Re: Otari MX5050 Biii-2 - REWIND- FASTFORWARD not working right.
« Reply #10 on: August 15, 2014, 11:53:27 AM »
Listen2Tubes,

     I will clean all of the items you mentioned. It does seem like an electronic malfunction to me. When I unplugged the counter board, it wouldn't get stuck any more. I don't want to leave it that way. I now have two reels to test on, used and not in the best condition but I can use them for testing. The fast forward and rewind works with the tape in the tape transport, like I said, only if I unplug the counter circuit board.

Regards,
Adrian Magana