Otari MX5050BII-2 RW/FF slows down and stops

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Blue Jinn

Blue Jinn

Rider of the ARPocalypse
Bought this refurbed a few years ago. At first I just thought this was a feature, that as the tape got to the end of a fast wind either way the deck would slow down to minimize tape damage.

But if, e.g. you're rewinding a tape the whole way it will get to pretty much rewound, maybe a 1/2" to a 1/4" of bulk left to go, slow down to an easy pace (which would be a nice feature) then slow to a crawl and then stop. But it doesn't stop with logic function "clunk" if that makes sense, the breaks aren't on, you can man handle the reels to keep it going. You can't get all the tape spooled up without manhandling the tension arms (which I don't think is really good for it) or faking it out and removing the tape from one of them. Any ideas????

This is not only weird, but frustrating and time wasting as well... And this was the expensive Otari, the POS project machine doesn't do this. This one has parts from a BIII which is why I originally assumed this was a feature.
 
If anyone is following this, tt the guy I bought it from, it is most likely the hold back tension. I have a manual, so will be looking at that adjustment.

Will update for future reference.
 
Old tape like Ampex can create this problem, but first I would check so both tension-arms + tape travel path are clean, gunk can also make the speed sloooow down.
 
Thanks, I don't think its the tape, as it will play fine, and the tapes I've run through it have been mostly non-backcoated (albeit old) Ampex: 641 and 632 and Scotch 177. (also some Quantegy 031, but it is Quantegy branded not Ampex.)
 
Otari tension adjustment is done on an arm connecting the break with the break solenoid. There are four holes on each arm to move the spring in or out. One for each motor. I don't have the fancy scale so this was going to be a swag. So I popped the hood, and started moving springs around. No joy, there are only 16 different combinations, and I must have tried all of them. I had my "parts" deck for comparison. Now I'm keeping my cool the whole time, and I remember that if I pressed hard on the right tension arm counter clockwise this would help. So I started to look again, and on the back side of the tension arm inside the chassis there was this little rubber piece about 4-5mm thick that was a sort of "bumper" for the tension arm, which kept it from moving all the way in the counterclockwise direction. My parts machine did not have this rubber piece. It looks like there is something like that in the exploded diagram for the BIII, but I didn't look at that until now, and I can't remember the orientation.

Nonetheless, this was causing just enough back tension to cause the machine to halt on RW/FF, (and the rewind motor to heat up too BTW) so I removed it.

Viola, RW/FF problem solved.

These machines are pretty dang precise in some ways we're talking a few mm's on the tension arm. I don't think not having the rubber stopper there is going to be a problem as I don't think it is ever going to move with enough force to hit home inside the chassis. (and the other machine is lacking it)

The 632 I used for teh test, got tore up pretty good on the overtensioned tension arm, so I've got some oxide to clean up now. (Also, the Otari's a great in a lot of ways, but the reel hold downs IMO SUCK!, they don't stay put, they are complicated spring, screw, spider web things. The Tascam's are way above, and I think Otari adopted something like that on the BIII/BIV series. (This is a BII)

Problem now is I don't have the fancy scale to properly set the tension otherwise, and I can't even remember what the damn thing is called. Telemprompter? Teleometer? So I put it back where I think it was before, (another lesson learned, I took photos last time when working on my Avatar to know what plugs went where...)
 
Well, not quite there yet, 7" reels, no prob, 10.5" plastic reels, no problem, metal reels, problem. 4 screws, two springs, another readjustment.....
 
Thanks. The adjustment is rather rough though, and the owner's manual actually uses a spring scale. (Which brings up an interesting point as the Teac manuals also have spring scale but the force is in g/cm rather than just g....)

I'm going to swag it for now, until I get the scale.

:-)
 
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