Otari MTR90 record head 10k tone fluctuates back and forth.

[Brian Roth]

Zenith also crossed my mind as well. The wear patterns (if visible) on the R and P heads might yield some clues. At one time, I had a couple of glass blocks I used for checking the tape path of a MCI 2" machine after the capstan motor was replaced. The idea given to me was to go from one surface the tape crossed to the next and see if I could feel any "rocking" of the glass block. IIRC, those MCI's had a number of surfaces the tape crossed. Left to right: input guide, erase head, record head, play head, exit guide and then the capstan.

A crude zenith check method involved "painting" a line of Sharpie on the head where the tape contacted, running some scrap tape over the paint for "x seconds/minutes" and then seeing if the Sharpie ink wore off in a rectangle or a trapezoid shape.

Bri

 

[RoadrunnerOZ]

It would also to good to see a scope on the signal going in and coming back off tape.
There is a mention re the Otari of the capstan roller motor frame being able to bend off alignment - worth checking the vertical alignment of all tape ride elements in the tape path. For servicing Studer A820’s, MCI JH-24’s (and also some other machines including 1/2”s) I had some setup gauge blocks and a flat 2” soft alloy bar for checking parallel between surfaces like Bri’s glass blocks - the bar was precision machined and polished and either rocking the bar or for fine checking used with a bit of engineers blue wiped on it, then gently sliding the bar against the surfaces to be checked would give an immediate visual answer. The alloy was soft enough and smooth enough to not scratch the heads

 

[gyraf]

..tape moving up and down as a function of tape tension points very much towards a bent tension arm. Routinely, these got bent when an inexperienced tech short-dropped a reel of tape onto it - so we replaced mainly the right side arms (tapes stored tail-out). Quite a few of them.

Recently, a friend of mine (no, I'm not naming anybody) who tended to a rather large fleet of MTR90's in the past century confessed to me that he had a 3-feet heavy steel tube that would just fit over the roller axle, that he'd use this to re-straighten those all-too-often bent tension arms. I wish I'd thought of this myself back in the days, replacement arms were both expensive and complicated to replace. And there's little to loose going this route..

Btw, have you noticed that the people that claim that violence doesn't solve problems are often the same persons that didn't even try with violence in the first place?

/Jakob E.

 

[tinn]

To me it looks like a mechanical and alignment problem.
Check if the up/down movement corresponds with any rotation of the rollers.
The rubber (PU) rollers degrade but should be in very good shape.
Less than a hair excentricity.

Best, Tinn

 

[RoadrunnerOZ]

Recently, a friend of mine (no, I'm not naming anybody) who tended to a rather large fleet of MTR90's in the past century confessed to me that he had a 3-feet heavy steel tube that would just fit over the roller axle, that he'd use this to re-straighten those all-too-often bent tension arms. I wish I'd thought of this myself back in the days, replacement arms were both expensive and complicated to replace. And there's little to loose going this route..

Great idea breaker bars not just for loosening wheel nuts. In the Luxury Supercar auto workshop I worked in we had an 8 foot breaker bar for undoing and torquing up the wheel locking hubs on Ferrari F40’s and the like. 470lbft of torque took 3 guys - 2 on the breaker bar and 1 with his foot on the brakes.
Out of alignment lifters on some tape machines I’ve repaired had caused the tape to stretch on one side after high speed spooling resulting in poor head contact.

 

[tinkerteks]

Working as studio maintenance tech in London from early 1990s I experienced Ampex ATR124, Otari MTR100, Studer A800 A820 and A827 two inch 24 and 16 track tape recorders. End of 90’s I worked in a complex with Otari MTR90s for a couple of years and they were good workhorses but not in my opinion quite in the same league. I don't remember one without some degree of HF wobble (to be fair at time Ptools taking over and they had done years of work in budget studios). The 10k wobble and shifting tape as you describe was commonly caused by bent tension roller guides. I replaced a few with spares from Thear Technology in the UK at the time. The pinch rollers were considered consumables and I believe you can still get from Athan Corporation. Bearings in any tape guides also critical and worth consideration. Athan have fantastic in-house expertise in this area. I would talk to them.

 

[RoadrunnerOZ]

From working on and using in the studio many different recorders over the years they all had their own foibles but consistent was the aging of roller rubbers, the wear and subsequent intermittent grabbing of dodgy bearings and the misalignment of guides and rollers (sometimes from tape reels dropped on them or some idiot leaning on them while cleaning heads) leading to uneven head wear and tape head contact, motor bearings that would heat up and grab causing tension issues, failing caps in motor control circuits, incorrectly set up servos - it’s a wonder we ever were able to record anything, but we did and constant maintenance was just part of the game. Not many people read the manual regarding periodic maintenance. One studio I worked in we had an MCI 2” 24 track and 1/2” mastering machine and the first thing before starting a session was to unseat and reseat all the record and repro cards otherwise they’d drop out randomly - the edge connectors had worn so far I think the plating had come off the pins. Sometimes a good bang on the card drawers would do a quick fix.

 

[MZFl]

Hello everyone. There seems to be a pulse coming from the supply reel when in play mode causing movement in the tape. I fixed the tape so it doesn’t get yanked up when in play mode. This seems to give a better response at 10k with slightly less movement of the vu meters it seems, however the issue is still there. Tape tension has been measured at 460g, reel height is in order. I’m not sure if it’s the rollers there doesn’t seem to be much tape slippage as I’m only 2 inches off the beginning of the tape when I zero search. The swing arms have been calibrated properly. What would be the cause of the supply reel pulsing like that. Video attached. Thanks for all the help everyone.

 

[Brian Roth]

What am I missing here? Indeed there will be some small amount of tension "bobbling" as the machine comes up to speed from stop. What I see in the video looks quite normal as it settles down very quickly.

This ain't digital playback...lol....that heavy roll of 2'" has to come from a dead stop to 30 (15?....whatever) IPS quickly, but it can't do it in 10 mS!

Or did I overlook something.....

Bri

 

[MZFl]

What am I missing here? Indeed there will be some small amount of tension "bobbling" as the machine comes up to speed from stop. What I see in the video looks quite normal as it settles down very quickly.

This ain't digital playback...lol....that heavy roll of 2'" has to come from a dead stop to 30 (15?....whatever) IPS quickly, but it can't do it in 10 mS!

Or did I overlook something.....

Bri

It does it the Entire length of tape

 

[Brian Roth]

It does it the Entire length of tape

Ahhhhh...OK. I was only looking closely at the movement of the roller assembly as the tape came up to speed. The bit of "rippling" of the incoming tape sure looks like it is at least partially due to the pack of the tape on the reel.

Or maybe not....that could be due to the tension roller not being totally perpendicular to the top plate/tape path.

Bri

 

[RoadrunnerOZ]

I seem to be seeing some slack in the upper part of the tape showing as surface rippling in the reflected light off the tape surface while playing as well as on take up. This would indicate either a roller or the capstan roller off true vertical tending inwards

 

[MicMan]

The tension roller looks OK - to me - but the tape coming off the spool appears to have been badly wound, or spooled. I don't think there's any variable-speed - or variable tension - spooling available on the Otari (unlike, say, a Nagra with a QGB big spool attachment), so fast-winding the spool contents onto the take-up spool, and then fast-rewinding *MAY* produce a better, as Brian says, "pack of the tape on the [supply] reel". But I'd also try spooling - forwards and backwards - your tape onto different supply and take-up reels. [I'm not sure if this Otari has a 'scrape' or 'anti-flutter' head ..Otari head arrangements varies between different models.]

When you say 'pulsing' I thought you meant a momentary speed, or tension, change in the rotation of the supply reel ..but the speed and tension look smoothly consistent, so maybe you mean, by 'pulsing', the changing 'ride' or position of the tape coming off the supply reel.

So check:

(1) Does this happen when using other reels on the supply side?
(2) Does this happen after you've rewound this tape onto a different supply reel (could be a badly centred core on that particular reel)?
(3) Have you tried using different tape-up reels? ..a misaligned reel core may affect the tape travel.
(4) Have you tried rewinding this tape, onto this same supply reel, but using a different machine ..preferably at a different speed or tension?

All these should be tried, to eliminate any fault with the supply and take-up reels (the physical spools with tape on them, not the spool platters on which they sit). And if no fault's found with the spools themselves, then check the 'upright-ness', the vertical 90º-to-horizontal attitude of both tape platters.

 

[RoadrunnerOZ]

As far as I can make out from earlier posts these tapes work fine on another machine, and also multiple tapes have been tried so presumably with the same takeup reel(s), but looking more closely at the videos you can see a distinct rippling of the tape surface more at the upper edge as the reflection curls and leans inwards, there is also that the ripple appears to to pulse as if it is in time with perhaps the reel rotation which could be an out of true reel hub - looking at the surface of the tape at the reel it seems to move in and out. Perhaps a longer video with the camera stable and a black chinagraph mark on the face of the reel to indicate a rotation cycle focusing on the tape at the supply reel.

 

[MZFl]

As far as I can make out from earlier posts these tapes work fine on another machine, and also multiple tapes have been tried so presumably with the same takeup reel(s), but looking more closely at the videos you can see a distinct rippling of the tape surface more at the upper edge as the reflection curls and leans inwards, there is also that the ripple appears to to pulse as if it is in time with perhaps the reel rotation which could be an out of true reel hub - looking at the surface of the tape at the reel it seems to move in and out. Perhaps a longer video with the camera stable and a black chinagraph mark on the face of the reel to indicate a rotation cycle focusing on the tape at the supply reel.

Here you go. It’s a different reel this time and there still seems to be a flutter occurring in the tape each revolution.

 

[MicMan]

Mmm. It's coming smoothly off the (different) spool this time - no 'pulsing' from the supply reel - but the tape seems to be fluttering up and down (..though it's out of focus at the tension roller, and so can't been seen clearly..) on the tension roller. Leaving this new, steady reel on the supply side, can you take an in-focus movie of the tape passing over the left tension roller AND across the heads, so that we can clearly see WHERE the flutter starts, how it travels across the heads, and beyond them to the take-up spool?

 

[RoadrunnerOZ]

There’s still rippling in the tape surface seen in the reflections off the tape - it’s as if there’s not sufficient supply reel motor back tension - possibly need to do a swing arm and servo cal - section 5.11 of the manual. I’d also check that the two set screws for reel table height adjustment on each reel motor shaft are set tight and square to the flats on the motor shaft see section 5.10

 

[johnsonic]

I was fighting a similar issue yesterday (on a MX5050 MKIII-8), was pulling my hair out. Tension rollers were straight, I had just turned the guide pins a bit for a fresh surface, heads have great contact / etc. For fun, I swapped the SM911 I was using out to ATR Master tape and it resolved itself. No idea why.

 

[RoadrunnerOZ]

Slip and grip with the 911 maybe

 

[MicMan]

The spec says:

Pinch-Roller-less direct drive capstan system with ±20% speed control. Constant tension servo-controlled reel motors.
Cue knob for variable speed tape winding (bidirectional) proportional to knob rotating

What happens when you reduce or increase the chosen speed ..any change in the tape 'ripple' or 'ride'? When the tape has started, there appears to be a clear 'wobble' after about 2 and then 5 seconds, and then again at 13 seconds, as the tape peels off the supply reel, almost like a splice going over a head.

Maybe this tape has been stopped and started so many times that the on-spool winding has become 'lumpy' due to short regions of different start-up tape tension. (I've had the same with 35mm cinema film being stopped and restarted on a 'cake stand' platter system, and thereafter it won't spool properly out of the centre of the spool and through a projector, due to regions of differently-wound tension.)

Can't think of anything else, sorry.