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Thread: Fostex R8 speed fluctuation-revised, with pics.

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    Fostex R8 speed fluctuation-revised, with pics.

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    Following on from this thread:

    https://homerecording.com/bbs/showthread.php?t=281264

    Ok Chaps, after ruling out sticky shed syndrome, the problem seems to lie with either:

    1. The pinch roller
    2. the drive belt
    3. the motor.

    Here is the pinch roller.



    I have a link to buy a new roller, but its in Japan, and it may not be the cause of my problem.

    Ok...the front of the machine.



    In this pic, I have drawn on where the drive belt runs, behind the facia.

    If you press play, the motor runs the untoothed belt, and turns the pulley with the capstan on it. the pinch roller closes on to it, which should pull the tape through, and it does, but on playback, there are massive speed and therefore pitch fluctuations.

    If I hold the capstan or the motor pully, the motor slows down and struggles to speed up again. if you give the capstan a quick twist, it will speed up again. If you hold the roller so that you stop it from turning, it will not start again, until you give it a twist.

    To me, in my admittedly unexperienced opinion, this seem like a weak motor.

    if the motor was strong, surely, if i held the capstan, it would make the drive belt slip.

    heres the motor from behind.





    I reckon its the motor.

    Anyone else have an opinion?

    Are these motors still available?

    Thanks in advance.

    Phil.
    Last edited by Mr Fruit; 04-09-2009 at 09:03.

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    When I first saw this I thought that the belt had melted, until I realised it was just scribbled on.

    As for the motor, it looks like Nihon was bought out by Johnson Electric in 2004. They don't seem to do anything comparable, though you might be able to get a NOS motor or something.

    What I have read is that it might be worth checking or replacing the drive transistors before you panic too much. I wouldn't know where they were on this machine, though.

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    Thanks for the reply, Mr morris, I keep noticing your name popping up on all my help threads, I appreciate it.

    Hmm, drive transistors would be way beyond my capability. I can take things apart, and reassemble with new parts, but thats about as Far as I go.

    Perhaps i'll have to do some research into a good UK repair shop.

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    Some pinch rollers have roller bearings in them, many don't and just have a bronze bushing like you have there so your pinch roller looks fine.

    In one of the pictures the pinch roller looks shiny, like its glazed. Is it hard and slick, or is it nice firm grippy rubber?

    Is the belt tacky at all? Hard/checked/glossy or is it firm grippy rubber?

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    Arrow The pinch roller looks hard and slick.

    That doesn't bode well for the belt, either.

    I'd say, replace the belt and try to recondition the surface of the roller with rubber reconditioner.

    Your problem description does not sound like a motor problem. The rubber drive components are usually the things to fail.
    Quote Originally Posted by Lt. Bob
    ... subtleties of sound make a difference to those who really listen.

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    I cant check the belt at the moment, because ive built it all back up, so i didnt lose any of the bits.

    The pinch roller is a bit shiny, I wouldnt say it was as grippy as, say, a bike brake block. Its certainly not new rubber feeling, but then again its a bit subjective....im not experienced enough to know its suitability, and the only way ill find out, is waiting for the shops to open in japan, as they are closed till the 10th apparently....

    That wouldnt unfortunately explain the reels stopping
    every now and again though, would it?

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    Quote Originally Posted by A Reel Person View Post
    That doesn't bode well for the belt, either.

    I'd say, replace the belt and try to recondition the surface of the roller with rubber reconditioner.

    Your problem description does not sound like a motor problem. The rubber drive components are usually the things to fail.

    I can get hold of a belt and a roller, but ive watched it play with the outer case off, and the belt doesnt slip on the motor pulley, or the capstan pulley.

    Capstan belt #FB17
    http://www.openreel.net/parts_1.html

    Pinch roller #PR13
    http://www.openreel.net/parts_3.html


    its just the reels/capstan stopping that is frying my head at the moment, making me think its not ONLY the pinch roller.

    Unfortunately, until ive bought the above items, theres no way i can find out....

    BUT if i pay 40 for the parts, then have to pay for the drive transistors to be sorted (as was suggested as another alternative solution above) , then possibly pay for a motor as well, and that being fitted, I'd have to have seriously thought about just getting another machine that just works...

    Sheesh i dont know, i see why people use digital now.

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    i see why people use digital now.
    Well, I suppose I see your point but good luck getting a 20-year-old computer to do anything for you, and I'd rather replace a pinch roller than replace a hard drive and reubuild the OS any day. Its all in your perspective I'd say.

    The pinch roller should be matte in appearance and should feel firm but grippy to your fingers. If it is shiny and smooth it needs to be replaced regardless of your current problem. That's my 2p. It is hardened and glazed.

    If it were me I'd be replacing the capstan belt and pinch roller since the latter should be done anyway and if the pinch roller rubber is at that state the capstan belt is suspect too...then if that doesn't help the problem you're no further behind since those two parts should be replaced at this point anyway IMHO.

    Then we can work on the capstan motor. Have you got a service manual for the thing?

    I seriously think we expect too much of this equipment at times. Stuff does wear out but they are complex electro-mechanical devices that require maintenance and upkeep...just like anything does in order to keep going. I've spent plenty of time tweaking my studio PC and researching driver conflicts and maintaining storage mediums...restoring backups because some file got mysteriously corrupted blahblahblah. Neither is a silver bullet. But like I said I challenge anybody to show me a 15, 20, 30 year old computer that is still running great, if at all. My Ampex deck has taken a beating before I got it. It looks like it was neglected and abused and was into a new life as a parts deck. It needs work but in the end it is going to work great and it is about 40 years old. Obsolescence is in decades rather than years with an open reel deck. Not trying to lecture you. Just a bit taken by your exhaltation of digital this early in the process...

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    Arrow 2 things:...

    1) I've not taken apart an R8, but the previous Fostex's reel tables were also belt driven.

    2) The reels do not pull the tape in Play motion, the capstan and pinchwheel do. The reels just provide take-up and back tension. If the capstan/pinch roller fail to move the tape, the reels will also stop accordingly. If the reels slow down or stop in FF/RW, it would still likely indicate a problem with the belts.
    Quote Originally Posted by Lt. Bob
    ... subtleties of sound make a difference to those who really listen.

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    The reel tables are indeed belt-driven on an R8 via toothed belts from individual reel motors.

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