Otari MX80 setup issues

jpmorris

Tape Wolf
Okay, I've been trying to get the Otari operational for a while now, and there is a persistent issue with the transport that is enough to make calibration a problem. I've just obtained a new Athan pinch roller, hoping that would fix the issue, since I didn't like the surface of the old one. It hasn't helped as much as I'd have liked.

Basically the problem is that the levels are wavering slightly when the MRL tape is played back. On 1KHz this makes the lissajous figure open and close slightly. At 10KHz it's completely wild. The tape seems to be riding up and down the transport which I suspect is the problem but I haven't been able to figure out how to correct this.
I might adjust the reel table height again now I've got the new roller, and I haven't yet attempted to adjust the pinch roller pressure, though according to the spring scale it is in the right ballpark anyway.

Here's a video - the camera autofocus wasn't terribly cooperative. The second half has a more steady shot of the tape wandering vertically.



Any thoughts or suggestions?

Other things that I could do with help on are:

1. During the pinch roller test, it says to fasten the tension arms in their highest position and then press PLAY. This does not actuate the pinch roller, though. I finally resorted to using the spring scale with a loaded tape, but this was not fun.

2. According to the manual, the bias A setting - for 456 - is adjusted per channel, but the bias B setting is global for all channels from a single adjustment. How's that work? Is it really global, or is it an offset from bias A? Put simply, if I never use bias A because I'm feeding the machine SM900, will I still need to calibrate bias A as a necessary precondition for the bias B calibration?
 
I can't say for sure if that tiny bit of tape "ride" is within spec...I've not noticed that on my deck, but then, I never had your problem, so I never really focused on it that much.

Your scope at 1kHz should be a solid steady line....and that dancing you are seeing would be OK if it was at 16kHz, but man, yours looks like it's completely flipping in/out of phase AND dancing all over the place at 10kHz.
I don't think the pinch roller is your problem (I got an Athan too....great roller...%#$@ expensive!!!).
I would first check the reel tables...like does the tape rub and shim on either reel in PB...(you might consider using a regular reel of tape instead of your MRL for these initial checks just so you don't damage the MRL.)
Then if the reels look level and even and no tape rub/ride there...check the roller guides.

The other thing...is the capstan. If that's not pulling even, or has any wobble to it, it might be the cause.

AFA the A/B thing...I set mine up for 499 on the B, and I never bothered to set the A....so no, you don't have to calibrate A in order to use B.
Not sure what manual you are reading, but that "global" thing may not act quite the way you are reading it.
I can review my manual and give you a better explanation in a bit.....
 
OK...as I thought...the A & B thing is purely for bias.
The A is preset bias for 456
The B lets you set bias for other formulations, for both speeds.
That "global" switch then allows you to flip between the two speeds, globally, without reseting individually...
...it has nothing to do with the A setting.

On the other issue...appart from any mechanical problems causing bad scope readings, I do recall you saying that you reprogrammed the EPROMs for the transport.
I do know from my conversations with the Otari tech that I use, and who rebuilt my spare transport and who reprogrammed all the EPROMs to the same, latest-greatest versions...he said that code was critical for proper transport operations and remote operation...and that even when redoing the EPROMs with fresh code, it's not always a 100% thing...that some of the EPROMs just won't take the code. He said that he has to toss one out of every few he does.
So...besides the mechanical...I'm wondering if there could be some electronic issue with the transport/capstan causing some irregular tape movement...?
 
I don't think the pinch roller is your problem (I got an Athan too....great roller...%#$@ expensive!!!).
I would first check the reel tables...like does the tape rub and shim on either reel in PB...(you might consider using a regular reel of tape instead of your MRL for these initial checks just so you don't damage the MRL.)
Then if the reels look level and even and no tape rub/ride there...check the roller guides.

Yes, I'll check the reel tables tonight. The rollers and capstan appear to be running true. I think I'll hook up a frequency counter and see if there are any speed fluctuation with the capstan, but the regularity of the problem is making me think that it's in sympathy with one of the larger rotating parts.

As for the EPROMs, I'll keep that in mind but it was still doing this before I replaced them.
 
As for the EPROMs, I'll keep that in mind but it was still doing this before I replaced them.

Oh.....

With the capstan, I think you can use the pitch percentage on the counter display to see if it's steady...though I'm not sure if that reading is being taken off the actual speed of the capstan or off the pitch control circuit.
I would expect it to be right off the capstan...so if it's holding steady and not fluctuating, it might answer that question.

Do you have a W&F meter...?
 
Oh.....

With the capstan, I think you can use the pitch percentage on the counter display to see if it's steady...though I'm not sure if that reading is being taken off the actual speed of the capstan or off the pitch control circuit.
I would expect it to be right off the capstan...so if it's holding steady and not fluctuating, it might answer that question.

Do you have a W&F meter...?

No, unfortunately. I'm looking into software measurement of such, but what I was going to do for starters was load up the 1KHz MRL test tone and see if the frequency varies. I'm not sure I'd trust the speed display - but I think it might be a good idea to hook a scope up to the tach and capstan testpoints, just to eliminate a few things.

And yeah, it took a few weeks for the roller even to be posted - in the meantime I've been calibrating the I/O, replacing the ROMs and doing various other tasks which don't rely on the transport being up to spec.
 
Are the guides height adjustable? The ones directly inboard of the supply and takeup reels? I had a problem with a Tascam 48 once where the rolling guides directly inboard of the reels were not perpendicular to the deck plate and were also not lines up with the guides in the headblock. what that ended up causing was the tape to "hop" slightly on the counter roller which in turn caused skewing in the headblock. All those guides you'd think would manage something happening outside the headblock but my experience is they are all interdependent on each other and if something is pulling down or pushing up distal to the capstan its going to be doing the inversion of that action at each point between the problem and the capstan. And this is especially true if a guide is not perpendicular to the deck plate. Just something to check out.
 
Are the guides height adjustable? The ones directly inboard of the supply and takeup reels? I had a problem with a Tascam 48 once where the rolling guides directly inboard of the reels were not perpendicular to the deck plate and were also not lines up with the guides in the headblock. what that ended up causing was the tape to "hop" slightly on the counter roller which in turn caused skewing in the headblock. All those guides you'd think would manage something happening outside the headblock but my experience is they are all interdependent on each other and if something is pulling down or pushing up distal to the capstan its going to be doing the inversion of that action at each point between the problem and the capstan. And this is especially true if a guide is not perpendicular to the deck plate. Just something to check out.

I just did an experiment using a flexible plastic ruler, and it looks very much like the static guides mounted on the headblock are both a shade higher up than the roller guides (impedance, tach, tension arms). Maybe the head assembly has been swapped out and put back into the machine too high...
 
Sounds like a good place to start. I know with all my tape machines I've strived for and been able to achieve tape travel that looks as though the tape isn't moving (no hopping around). I'm sure you can get that with your MX80 too. Keep us posted.
 
Well...you can remove the head block without any concerns....just make sure you're unscrewing the nuts that hold it, and not the heads. It won't mess with the head alignment or anything, since that's all part of the block. Then see if there are any kind of washers/shims under the block that allow you to adjust its height.

Also...I know the reel motors have washers that let you raise lower their height, when you lift them up, you will see them (be careful, they stick to the inside of the sleeve sometimes, or the top of the spindle, and are easy to drop off into the bowels of the deck.....but you can use any kind of washer, as long as it fits inside. The motor doesn't spin on the washer...it's just there to set the height...So I think on one of them I have a mica washer and the other has a fatter metal washer, and I've had to adjust one of mine reel tables...as it didn't match the other one and the tape was rubbing the flange a bit.

I'm not sure about the roller guides though...I've taken them off, but can't recall if they have the same washer setup for height adjustment, though I'm sure there are ways to do that even with them.

Point being, if the head block is in it's correct position with no room for adjustment...then you can adjust the guides/reel tables instead to match the block....though I can't believe that small "ride" would cause that, since MRL are recorded full-width, and there are no "tracks" that have to match up your head tracks perfectly.
So....that to me still seems like a speed fluctuation issue rather than the tape ride....though I guess the tape ride could potentially cause some speed fluctuations, but I would think it would take a lot more "ride" and the tape would have to be rubbing at it's top/bottom most points.
I still feel like it's electronic and not so much mechanical.
Anyway...just tossing out some ideas...I could be way off on that. :)

Than again....did you only adjust the azimuth screw...or did you also move any others that adjust the heads?
I was told by JRF Magnetics who did the re-lap on my head block and optically aligned the heads, lifter, roller and guides...to ONLY adjust the azimuth screw....nothing else.
 
Point being, if the head block is in it's correct position with no room for adjustment...then you can adjust the guides/reel tables instead to match the block....though I can't believe that small "ride" would cause that, since MRL are recorded full-width, and there are no "tracks" that have to match up your head tracks perfectly.

Yes, it looks like I may have to try shimming the roller guides since the headblock is as low as it can go. The reel tables I don't think need any adjustment beyond what I can achieve with the two allen screws accessible from the reel clamps anyway.

I've checked the capstan motor servo and the duty cycle was a little off but not significantly so and I've tweaked it a little anyway. I can try checking the tach quadrature tomorrow, but I'm not convinced it's an electronics issue.

Studying the ch2 and ch23 waveforms side by side (as opposed to the lissajous figure) the ch2 waveform varies in amplitude and also in its phase relationship with ch23 - 23 is rather more steady. I'm not seeing the waveforms compress which I would expect to see if the speed was varying significantly, they just seem to be moving around. But it would suggest to me that there may be a head contact issue towards the top of the head stack.

Than again....did you only adjust the azimuth screw...or did you also move any others that adjust the heads?
I was told by JRF Magnetics who did the re-lap on my head block and optically aligned the heads, lifter, roller and guides...to ONLY adjust the azimuth screw....nothing else.

Absolutely. I just used the hole cut into the cover and shone a light in to make sure I was getting the right screw.
 
OK...here's another thing to check....the flutter filter roller that sits in-between the two heads. That roller does a lot to keep the tape flutter-free. If it's not spinning true, or smoothly/freely...it could upset the tape flow.

Oh...for the reel tables, if you do adjust them, don't simply raise/lower them and then tighten the two screws to hold them in place.
You want to completely lift the reel table off the spindle, and on top of the spindle (or they could stick inside the spindle hole on the reel table) are the washers/spacers that let you set the height, or where you would put the washers/spacer if there aren't any if you need more height...but there should be some there, so be aware when you lift the reel table off.

IOW...you want the reel table to sit right on top of those washers/spacers (or the spindle if none or needed) with it's weight, and THEN you use the screws to just to hold it in place from spinning around the spindle....and not to hold it suspended above the top of the spindle for height adjustment.
If you just raise the reel table and it's up off the spindle, those two screw and their grip on the spindle will then be taking all the weight of the reel of tape. You want the weight on TOP of the spindle.
Am I making sense....?
 
Oh...for the reel tables, if you do adjust them, don't simply raise/lower them and then tighten the two screws to hold them in place.
You want to completely lift the reel table off the spindle, and on top of the spindle (or they could stick inside the spindle hole on the reel table) are the washers/spacers that let you set the height, or where you would put the washers/spacer if there aren't any if you need more height...but there should be some there, so be aware when you lift the reel table off.

IOW...you want the reel table to sit right on top of those washers/spacers (or the spindle if none or needed) with it's weight, and THEN you use the screws to just to hold it in place from spinning around the spindle....and not to hold it suspended above the top of the spindle for height adjustment.
If you just raise the reel table and it's up off the spindle, those two screw and their grip on the spindle will then be taking all the weight of the reel of tape. You want the weight on TOP of the spindle.
Am I making sense....?

I hadn't thought of it that, way, that's a good point. And yes, I'll check the flutter roller as well.
 
No joy so far, but I've just noticed there's still an issue with the tape path. I'm going to try a different shim setup tomorrow, I think.

Something else that has come up, I did a check on the tension sensors tonight. The takeup sensor reads something like 3.5v on CP5, and with a little adjustment of the gain was happily lined up from 0-10v.
The supply sensor reads 2.2v on CP1, and the gain adjustment tops out at about 8.9v.
The sensors appear to be aligned according to the instructions.

Any ideas?
 
My Otari tech told me that unless I'm seeing specific problems...not to mess with every sensor, pot, switch...etc.

I took his advice. :)

There's a lot of mechanical stuff that you can tweak...but it's also easy to let it get away on you.
I guess what I'm saying is focus on a specific area instead of simply messing with everything in the hopes of finding something that has a positive effect on your problem.

Have you talked to your Otari tech...?...I seem to recall you said you had someone who knew Otari machines.
He may be able to point you in a specific direction...and then just leave the other stuff alone.
 
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