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