Teac 8516 / 1" tension woes

P

pdmillar

New member
Hi all, long time listener / first time poster here.
I acquired a Teac 85-16 after making a lot of recordings with my pair of Fostex R8s over the last 4 years.
Heads were relapped by JRF and I replaced the bearings in the motor myself.

After using the machine on a bunch of sessions since last July, I notice there's a disturbingly uneven pattern the tape is polishing the head in. It seems like the tape tension on the low side must be higher than the high side, but I have no way to ascertain if this is the case. I want to fix this before my heads wear out unevenly.

(looks like the images are huge, might want to right click and view)

View attachment 86601

Note in this one that the tape is wrapped loosely around the bottom of the supply tension roller... that's the only place I can really tell that it is stronger on one side. If it's bent, would that skew the tension up to the capstan?

View attachment 86602

Any members here with experience working on wide transports? (Sweetbeats?)
I have fixed loads of 1/4" and 1/2" decks in my time as an electronics weirdo but tape this wide seems to present its own challenges.
P.S. is it normal for a wear pattern to appear that quickly with new/relapped heads? This is the first personal machine I've had where I would have been able to witness that. The tape I'm using is 456 manufactured in about 1995, exhibiting no signs of binder breakdown. But I'm not absolutely sure it's past the cutoff date for the bad formula.
 
Hey there. Sorry to hear of your trouble.

Nice to have an 85-16 owner chip in though.

Can't see the attachments? Might be because you have only one post? Can you post them up elsewhere and put links here or you can email them to me directly (PM me for email addy) and I'll post them here.

Could be a few things. I'd hope (Tim) Beck might chime in on the tape you're using...IIRC 1994-ish is the SSS cutoff date for Ampex/Quantegy tape...but be mindful (unless YOU bought the tape new yourself and can verify) you have no way of knowing what's actually on the reel.

Questions:

• How has the tape been stored?
• Has the 85-16 been moved or been subject to ANY trauma since it was last working properly?
• You replaced the bearings yourself...you talking about the capstan motor?? What bearings/brand did you purchase? Are you confident the motor went back in exactly as it came out and were there any shims between the motor and deck plate?
• What's the condition of your pinch roller?
• Can you take a good bright LED flashlight and, positioning your eye and the light such that the capstan and pinch roller are in between, manually press the pinch roller up to the capstan to see if the light reveals a greater gap at the top than at the bottom?
• Is the tape getting crammed or is it curling at the bottom of guides in the headblock?
• Are you *sure* the headblock went back in properly?
• Is the tape the same tape you used before when it was working? Do you have different tape you can try?

Maybe seeing the pics will help answer some of these questions. But generally speaking, if it was working and now it ain't right, you make a list of what's changed (headblock has been out and back in, capstan motor has been out and back in with new bearings, tape is the same or different?), and it is related to one or more of those elements, period...process of elimination.
 
I've not tried this, but in case it's useful, a trick I remember seeing mentioned in the Revox B77 service manual was to draw a vertical line on the head with a Chinagraph pencil and play back a scrap tape for a little bit. How the line wears down will show you if you've got a problem with the zenith.
 
Oh, oops. Here are the two images
IMAG1060.jpg
IMAG1069.jpg
1) The tape was stored in a house along with the machine. The whole lot came from a Vegas showtune composer's estate (no kidding!) So far none of the 8 reels I picked up have shown any sign of SSS at all. They were all still in the plastic inside the box when I got them. All dated late 1995. A few others from 1992 did stick to the guides a bit so I'm not using those.
2) I would not say it was ever working "properly"... heads had the same sort of trapezoidal wear pattern when I got the deck.
3) Yes, the capstan motor. I replaced the bearings in the motor with the same type NSKs (or as close as I could get) - I couldn't get the flutter down, and eventually figured out that the shaft was somehow out of round. I found another motor on eBay, it arrived with the FG coil pcb damaged and I had to put the two together to make a good one.
4) Two pinch rollers came with the machine and they both looked good, I believe one of them was brand new. That's the one on there now.
5) The alignment of the pinch roller and capstan I am not sure about. I have tried shining a light between them, and sometimes it looks like they are not aligned, but the roller has only one bearing at its midpoint and can pivot on the shaft just a little bit.
6) Tape actually looks good passing through all of the static guides
7) I'm sure that the block is back in the way I got it, unless there are ever shims on headblock mountings (doesn't seem likely to me given the odd geometry of the 3 mounting bosses in the deck casting). I never touched the head alignments at all, since John was supposed to have done that with the optical jig, that's the last thing I want to mess up. They don't appear to have a screw adjustment for anything but azimuth? (Height and zenith have to be controlled with shims or something? Teac heads are kind of stupid). I wonder if they actually are exactly 90 degrees to the block.
8) I've only ever used these few 456 reels and a 1" MRL I borrowed from work. There are a few GP9s there right now that I might try.

Thanks for the ideas. I think the next step may be to try to find a glass shop to make an ultra-flat alignment block. Any advice on that?
 
Oh, yeah - I had painted the two stationary guides on the head block a while ago with a permanent marker, to see how it would wear away (visible in the first picture) - I don't think either of them resemble the trapezoid at all?
 
1) Okay. It might not hurt to try the GP9 just to see if it behaves any differently.

2) Okay...so there is an historical issue here...

3) Yikes. But the flutter issue resolved?

4) Okay. Check!

5) Okay, but there are two issues here...even if the pinch roller can self align to the capstan shaft, if the shaft is out of alignment with the rest of the path it will cause issues, and also it is still not good if the pinch roller and capstan shaft are out of alignment. Can you put up a picture of the pinch roller mounting bracket? I want to see how it is mounted on that machine.

6) Okay, but can you put up a picture of the tape going through the static guides? And more light for the pics would help.

7) The Teac heads aren't stupid IMO. The are typical of many 1" and wider heads in that the height and zenith are fixed. This is actually a good thing. The azimuth is semi-fixed, and the wrap angle is adjustable. You are quite correct not to mess with a thing once it comes back from JRF, except for fine-set azimuth is one I'd check every now and then. Have you contacted JRF by any chance?

"I think the next step may be to try to find a glass shop to make an ultra-flat alignment block. Any advice on that?" I'd get a small precision square from a tool house and check the tension arm rollers, the counter roller and the capstan shaft against the transport mounting plate. And then if possible check the headblock components against the headblock (guides, heads).

And I'd contact JRF to see if John has any ideas or if they've run into this with the 85-16. Make sure he understands the heads displayed a trapezoidal wear-pattern before the relap.

"I had painted the two stationary guides on the head block a while ago with a permanent marker, to see how it would wear away (visible in the first picture) - I don't think either of them resemble the trapezoid at all?" I wouldn't necessarily expect them to show trapezoidal wear...harder material than the head cores.

I really want to see what the tape looks like in the static guides in the headblock. We're trying to narrow down what's out of alignment and whether you've got an uneven tension issue, or if the heads, even though fixed, are somehow out of alignment regarding zenith. This would be really strange and, regardless, they should be lined up to the static guides. John French wouldn't have let it out the door if they were.
 
i see curling on the bottom of the tension roller on the picture.

Also, even if you have good zenith if the tension is high enough it will always create that trapezoidal wear sooner than later. So how high is the tension on playback mode ? get a tentelometer if you can, you should be around 180g/m no more than that. One way to check it without the tentelometer is to check how high on the range the tension roller is pulled, this is very critical on the MS16 as well which is a newer version of this machine with some shared components.

The damage is done at this point, so it is about correcting the problem, you need to get absolutely no curling on any of the tape tension roller and the right tension (too low tension will result in the tape wobbling up and down a little and less travel of the tape tension roller) The tentelometer can be found for less than $100, given the hard to find status of these heads it is probably a good idea to get one on ebay. There should be a transport adjustment section in the manual, tape roller height and azimuth is adjustable i think on these models too.
 
in re: Sweetbeats

3) Flutter is a lot lower than it was, but it's still audible on certain test tones. I'm hoping that what remains is related to this tension problem. I know that some people say the capstan servos in these machines aren't very good.
5-6) Will do when I get home.
7) I talked to John about this issue back in December and he said "a lot of Teac heads exhibit a wear pattern like that", without really going into how I might correct it. He mentioned that he would normally use shims if zenith needed to be corrected. It doesn't look like any were added.
I'll take some more pictures tonight. I'm also purchasing one of those precision squares, that's a good tip.
 
fgonza2 said:
i see curling on the bottom of the tension roller on the picture.
Click to expand...
Yes, I was trying to illustrate that - it's obvious when tape is rolling that the tension is a lot higher at the TOP of the supply tension roller than at the bottom. (the opposite of the condition at the heads?) I'm not sure what happens after it crosses the second roller.
fgonza2 said:
Also, even if you have good zenith if the tension is high enough it will always create that trapezoidal wear sooner than later
Click to expand...
I was not previously aware of this. I've got to get my hands on a Tentelometer now, I have never really been able to check tensions properly. Probably a good investment since I do want to keep working on tape machines. I do have a copy of the service manual here.

I did attempt to make sure it wasn't set really high, since the heads were so worn when I got it. I recorded a 10K tone and tweaked the tension servo down to the point just before the repro started to drop in level. This was after the heads came back relapped. Is there anything correct about that idea at all?
 
pdmillar said:
Yes, I was trying to illustrate that - it's obvious when tape is rolling that the tension is a lot higher at the TOP of the supply tension roller than at the bottom. (the opposite of the condition at the heads?) I'm not sure what happens after it crosses the second roller.

I was not previously aware of this. I've got to get my hands on a Tentelometer now, I have never really been able to check tensions properly. Probably a good investment since I do want to keep working on tape machines. I do have a copy of the service manual here.

I did attempt to make sure it wasn't set really high, since the heads were so worn when I got it. I recorded a 10K tone and tweaked the tension servo down to the point just before the repro started to drop in level. This was after the heads came back relapped. Is there anything correct about that idea at all?
Click to expand...

fgonza has several good points. I wasn't sure if that was curling on the supply tension roller, but yeah...that's not a tension issue necessarily, that's a mechanical alignment issue in the tape path.

I suggest you go through the manual as suggested and align the tape path. The tension roller heights should be adjustable. Just follow the procedure in the manual.

As far as tension setting using HF "droop" (that's my term for it), that is certainly one way to do it. If it was me I'd set it to factory spec using the Tentelometer as outlined in the manual and then experiment with HF droop from there...too many variables and you've got an issue with wear so get it setup according to the manual and then once its working right you can experiement.

My 2p.

Using the HF droop method is the way I do it on my Ampex MM-1000 since there are no instructions for how to set tensions using a Tentelometer and the method using spring gauges in the manual is just too coarse a method.
 
The manual doesn't have any instructions w.r.t. tape path alignment at all!! Argh.

I decided to look at that pinch roller again:

IMAG1076.jpg

When the solenoid is pushed in by hand the bottom edge makes contact well before the top edge. It appears (no tools to really check this for sure) that its shaft is not parallel to the capstan.
When it is fully engaged, the bearing in the middle must pivot a bit. I didn't think that ball bearings were supposed to be able to put up with much of that - do you guys think it is likely that the pinch roller is exerting more pressure on the bottom edge than the top?

I also attempted to photograph a slit of light between the repro head and the capstan (not easy:)

IMAG1082.jpg

It didn't particularly look like they were out of alignment.
 
Alright. Good information. Would really like to see a pic of the tape behavior in the fixed guides in the headblock during play mode.
 
Oh yeah, I got pictures of those too:
IMAG1086.jpg
IMAG1090.jpg

That's the one part of the machine that seems to be working fine. The tape passes through silently and doesn't curl at the edges or anything. Left one looks a bit dirty in the picture, sorry, just noticed that.

After I took that pinch roller picture I disassembled that mechanism... my initial thoughts is that the die-cast roller arm must be somehow warped. I have two pinch roller shafts (they lightly press fit into the arm). I pressed the other one into the hole in the arm for the post coming out of the deck that it hinges on, and they quite obviously weren't parallel. Huh. There doesn't appear to be any way to adjust that, and it's much too strong to be able to bend it. I sent Teac an e-mail seeing if I could get another one (p/n 6014103000) but I bet they're not going to have it.
 
IMAG1093.jpg
Here's the pinch roller mechanism... there doesn't appear to be anything to adjust except for the distance the solenoid pulls.
 
Okay, this is crazy-talk, and I'm reluctant to suggest it at all, but in lieu of a better idea, but would it be feasible to alter the rest of the system to match the pinch roller shaft? Shims on the mount of the capstan motor to hold it at a new angle? You'd have to do the same with the head assembly as well, but those are usually attached via four corner screws.
 
Well, I've contacted Teac and the guy that had the parts transport who I bought the capstan motor from, to see if I can get a new pinch roller arm. That seems to be the most obvious thing to try right now. The head block has three screws and so does the capstan motor, and they look difficult to shim.
 
I'd be really hesitant to try and shim the block or the capstan motor. The pinch roller position does not look right and if you're saying it may indeed be tweaked I'd be going that route as the "right" solution. If you can't find new or used, consider removing the existing arm and taking it to a machine shop to see if they can straighten it.
 
The manual doesnt have any tape path alignment procedures? Are those pages missing, or were they just never there?
You said you took the capstan motor completely out and replaced the bearings?

I believe the capstan motor has a tilt adjustment. In your pictures there is red torque sealant on the capstan motor mount screws. That generally indicates an adjustable interface, as the solenoid mounting screws are.

The manual for my ATR 80 covers the adjustment of capstan tilt, but unfortunately comparing the pictures of an ATRs capstan mounting scheme with your pics shows two different animals.
 
They were never there, not in the physical copy of the manual I have or the PDF of the 85-16B manual.
I don't believe that there is any way of adjusting capstan tilt on this as it's designed. How is it adjusted on the ATR-60? By torquing the screws differently? There isn't anything between the deck plate and the motor except the top part of the motor's shield (a flat circular piece of metal)

I called Teac today and they actually had a replacement pinch roller arm, so I ordered it - will report back when I get that tried out
 
You must log in or register to reply here.
Back
Top