Tascam 38 problem - capstan motor?

P

paperhatrecords

New member
Hi friends,
So I purchased a 38 about a month ago, and the initial problem was the deterioration of the pinch roller. I got the pinch roller re-rubbered to specification and it looks great, but for some reason whenever I load tape it still seems to just lock up after I hit play. There seems to be a lot of tension between the pinch roller and the capstan, and turning the pinch roller with my finger takes a bit of effort (maybe that's how it is supposed to work...I'm new). The capstan does not seem to turn on its own while play is engaged. My immediate guess is that the problem has to do with the capstan motor, but wanted to check to make sure that the tape locking up completely is the symptom of a dead capstan motor. If so, can someone walk me through taking it out of the reel-to-reel without damaging everything? After I get it out, I can post pictures and we can confirm it's shot. Then I'll need help installing a new one after I get one. I'm new to this all but want to get my hands dirty as long as it doesn't destroy my r2r.
Thanks!
 
The capstan is not direct-drive. It is attached to a large flywheel, and this flywheel is powered via belt. If the motor has stopped turning you would still be able to rotate it. It may take a bit of effort as the flywheel is pretty heavy, but it should not be almost impossible. You will likely find, once it moves, that the inertia of the flywheel keeps it turning for a bit.

If it is jammed, if it does not feel like what you'd expect in turning a large flywheel, there's something wrong.

Chances are it's to do with the belt. If the belt has disintegrated and tangled up the fly wheel it would act like you've described. If it has melted completely and gummed it up that may also be the reason. If the motor is running but the capstan is just turning freely, the belt has probably slipped off.
Expect that you'll need to replace it, which isn't too hard.



Getting the front off is somewhat tricky but not impossible. I managed it on my '32 before I discovered the exploded diagrams at the back of the manual :-S

Basically, you remove all the hex screws around the edges and stuff, and then you remove the knobs, pinch roller and everything else that may prevent the cover lifting off. If it's like the '32, there are two gotchas:

1. The counter module. At the top of the counter display is a small glass nipple. When removing the cover, make absolutely sure that you do NOT knock this little glass bit! If the glass breaks, the vacuum will be lost and the display will be destroyed. Maybe you could get it working again with a vacuum pump and a skilled glassblower but I wouldn't rate your chances.
You might have to find a replacement VFD or design a counter that uses LEDs instead. If you know someone with digital logic skills is might be a fun project :P

2. The varispeed control. Underneath this is an internal bolt. You will need some needle-nosed pliers or something to unscrew it. It can be done with sidecutters but it'll tend to score the sides. This internal bolt is typically the final bit which stops the panel coming off.

EDIT EDIT:

Once the front panel is off, you'll probably need to remove the headblock to get at the capstan system. All the heads are mounted on a single chassis which IIRC is attached to the rest of the machine with 4-6 corner screws. You just need to unscrew these and the entire head block will come off as a single unit. Assuming it doesn't get bashed, it should not need realigning afterwards.
 
If you're using older tape stock, sticky shed syndrome can also bring the transport to a grinding halt, even in a wind mode if the tape is badly degraded.

Whatever testing you do, make sure its done with a spotlessly clean tape path and fresh, new tape...otherwise all bets are off.

Cheers! :)
 
Thanks for your fast response jpmorris!

Actually, a little change to my original post: if I take the pinch roller off and hit play, the capstan motor does not move - however, if I push it with my finger it gets going and does turn at a constant pace. I'd assume the tape would activate this turning motion, so maybe the capstan motor is ok. But it does take a lot of tension to turn the pinch roller and the capstan does not turn on it's own with the pinch roller on. I'd assume the new rubbering was done to the correct dimensions (the guy specializes in this), so perhaps it's a belt or something... the tape just won't play.

I don't know. Maybe I'll cop out and take it to the local pro audio shop... thanks so much for your help though!
 
Hey Ghost of FM,

I've been vaguely aware of sticky shed. When I bought the 38, it came with a bunch of old tapes. I have been of the mindset that I could use these tapes just long enough to make sure it is working properly and from then on only use new SM911 tape. The tapes I'm testing don't look very deteriorated or have any noticeable stickiness and the tape head is near perfect. Apparently the unit wasn't used very much, but I suppose the stored tape could be the problem. I just don't know enough to diagnose it I guess...The rewind and fast forward work just fine, and play does make the reels rotate fine and as I mentioned above, the capstan turns with a little push. Hmm...

Thanks for your help!
 
Try this. Take the tape off and make sure the pinch roller is disengaged. Check that the capstan turns relatively freely if you turn it manually.
Then, with the tape still off and everything still disengaged, move the right-hand tension roller up. This will activate the capstan motor (since the deck will assume there is tape loaded). Does the capstan start to spin or does it still need help to start even with the pinch roller completely disengaged?
 
Will the capstan turn without a tape loaded on the deck? You can get it to turn by raising up the right side tension arm which has a switch in it to turn on and off the capstan motor.

If it does turn that way, on its own and offers decent resistance to stopping by rubbing your finger against it then we can eliminate anything wrong with the capstan, its belt and it bearings.

If it doesn't turn, then the belt that drives it is the next suspect. Rubber belts degrade and stretch with age and use and do need to be changed every 15 to 20 years.

If after a belt change and it still not spinning, then you have to look at electrical issues including the motor itself which might be clogged with gunk such as dried up lubricant mixed with dust that turns into a gooey mess.

Old tape stock, even unused tape can also fall prey to sticky shed. The tape glues itself together and makes it almost impossible for a healthy transport to work with it as the resistance is too great. This is why fresh tape is a must have item for any real testing.

Cheers! :)
 
When I raise the right tension roller with the pinch roller disengaged, the capstan does not move on it's own. However, once I give it a little push manually though, it gets going at a regular pace. Once it's turning, it keeps going (resists stopping) even when I press my finger against it. So it seems in between the two. If it's supposed to start on it's own it isn't. With play activated, and the pinch roller attached, it does not start moving even when I give it a push...(If it's helpful, I should also note I guess that when disengaged, the pinch roller rotates very freely when spun.) Thanks guys!
 
I have changed about 8 belts in the last few years and I have seen 3 differant scenes when it comes to belts.
First they can where out and just fall off but it doesnt sound like that is the case here. Second they can get gooey and kind of stick to everything they touch.
That could be the case with yours or they can stretch and they dont get a good hold of the pulley,s. That could also be the problem with yours. I would stop turning it on now so that maybe you dont burn the capstan motor up cause it is not the easiest thing to find. But belts are so take your time and take the front of the machine off whith it laying on its back.
Good luck with your 38
 
Belt Change visual Aids

sweetbeats said:
Yeah...I think itstime to open 'er up and get your squinties on the capstan belt. I'll stop there.
Click to expand...

I found these visual aids to be helpful when I changed the belt on my 38 just a few weeks ago:
youtube video:
https://www.youtube.com/watch?v=RU-nip_OGuM

blog:
http://velvetdreamstudios.spaces.live.com/blog/cns!7F6F3FB1C4798340!475.entry

its not really difficult even if you've never done anything like it before. You'll likely want to clean the belt path (flywheel etc) with Isopropyl while your there if the belt was all sticky.

the blog also describes cleaning / relubing the tension arm assembly, which mine needs as well. (the machine seems to work regardless of the neglect of these, but I guess its easier on the tape at startup if they're not all gunked up). I've got a 34 to do this on as well, so I guess I'll do them both at the same time here pretty soon.

good luck!
 
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