Otari problem

H

halfbird

New member
I recently acquired an MTR 90 mk.II with the following problem. The supply reel seems to be ever so slightly off center so that with every rotation, the level of signal drops about half a db on the meters. It's not audible to my ears but makes calibration something of a pain.

I assume this is not an easy repair or else the previous owner would have done it long ago. Anybody have a similar experience or know how I might remedy this myself?
 
Are you saying that:

  1. The reel table is eccentric, or
  2. The reel hub adapter/hold-down is eccentrically mounted, or
  3. The tape reel itself is eccentric?

Bear in mind that I don't own now nor have I ever owned/worked on an Otari deck, but for the first issue in the list on my Tascam decks I've been able to get the reel tables to spin concentrically by repositioning them on the motor shaft or by taking the reel table apart (the face of the table mounts to the reel table hub by three screws...I just took out the three screws and rotated it by 120° and then tried it again to see if it helped.

If it is #2 I just loosen the center-screw that holds the reel-adapter to the reel-table, slightly shift it in the appropriate direction and retighten repeating as necessary until it spins concentrically.

If it is #3, keep in mind that many reel flanges, especially the thin three-screw flanges, are eccentric relative to the reel hub. If the hub is spinning eccentrically relative to the reel table/hub adapter, stop the transport, loosen the hold-down and shift the hub slightly in the direction it needs to go, but don't judge whether or not the reel is spinning concentrically by how the flanges look unless you know for certain that the flanges and the hub are concentric to each other. Every time I load a reel I put the deck in EDIT mode, position myself at the side of the deck and look across the top of the reel I'm working on; I look between the flanges so I can see if the tape wrapped on the reel hub is moving up and down (eccentric), or if it is nice and steady (concentric).

I just know in my experience it takes some time and tweaking to get it right. 6-screw precision reels fit on the reel adapter more snugly and are a bit less of a headache with all of this as long as the reel adapter is spinning concentrically.

Couple questions:

  1. Have you considered that your back-tension might be off? Try this...if you have a cal tape, reproduce a 10kHz tone and then, while watching the VU meters, apply light back-tension to the supply reel (like just letting a finger drag on the reel flange)...does the output level increase? If so you may need to increase the back-tension.
  2. Does the 0.5dB deviation happen across all tracks? If not, maybe it is a tape path alignment issue. 0.5dB deviation especially at higher frequencies is not that much an issue and may be expected particularly on edge tracks.
 
Thanks for the reply, SB. I do believe it is the reel table, according to the previous owner. I'm a bit concerned about doing more harm than good by trying to adjust that myself but maybe I'll give it a shot.
 
Hmm...possibly a bent motor shaft then (if it has been a known problem)?

I dealt with that too.

Not trying to push you to get in over your head...wish I knew more about Otari decks but...

Have a look at it like you said. you won't hurt anything doing that. Maybe it is a simple problem, and if not it sounds like Hi_Flyer has a good contact there for you.
 
ok... i fail to see how the supply reel moving eccentricly causes the level to drop... and if i read you correctly it continues to drop with each successive rotation???? any body willing to explain this to me????
 
My line of thinking is that if the back tension is low, and depending on how well the tensioners are responding, and depending on how the tensioners are configured (i.e. above the heads, or off to the side below the reels, etc.), changes on the hub position, particularly as it rotates so that tension increases could contribute to that deviation. That's why I asked what happens when he does the wrap test (reproduce a 10kHz tone and slightly increase back tension on the supply reel) I've experienced this on my 58, particularly on edge tracks. You may not have read the whole debacle in my 58-OB Story thread but I've done battle trying to get the proper back-tension. Improving that situation as well as using a precision reel and dickering with the reel tables and reel adapter has improved the situation significantly.
 
seems to me that should be a freq response problem not level... and why would it continue to degrade over time??? why wouldn't the capstan counter this to some degree?? assuming it isn't skewing over the heads you'ld think all the supply reel needs to do is give a slight back pressure so the tape doesn't spill out as the capstan pulls it through... no??
 
You are not incorrect, but what you are saying doesn't entirely cover what I worked through. My 58 specs back tension at 75-85g, which feels pretty tight on the tape actually...it was running at 20-30g, and so I wasn't getting the optimal tape-to-head contact...the slight cyclical increase in back tension that occurred as the supply reel rotated eccentrically (and it was enough that it wasn't getting absorbed quickly enough by the tension arm) was enough to see level variations. You are right that it was more pronounced at higher frequencies. I was able to reduce the issue by doing what I said above. Hope that helps to explain...I think my case was extreme because the back tension was so low, but, again, because I had that experience I thought to put it out here for halfbird's consideration.
 
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