Fostex G-16S lazy supply motor on rewind

[niva]

Hello!

I am worried about my Fostex G-16S on rewind function. It can barely wind back the tape when the supply reel is almost full in other words, at the beginning of the tape.

It is supposed to be "mechanically aligned" but I bet the 3M 996 tape I am using is thicker than the Ampex 456 it is supposed to be used with...

I know there are TENSION trims under the bonnet, especially one for the REWIND function on the supply reel side. I am wondering if I can give it a little more without screwing the machine up...

Thanks for any input!

Guillaume

[2N1305]

Salut Guillaume,

(tu t'attendais pas à ça hein?!)

Ben, euh, Well, what I can suggest is that you at least measure the voltage applied to the Take up reel motor while in Fast forward mode. This should be (I'm assuming by design it is) the same voltage applied to the Supply reel motor (in rewind mode). Then measure the voltage to the supply reel motor in rewind mode. you see where we're going here, right? They should be equal.

I hope you have a multimeter. Some people here think they can troubleshoot stuff without a multimeter. Yeah...mmk. Good luck. also I doubt the type of tape will do anything unless it is thicker in which case it will add weight. But I am thinking the motors, rather the drive circuits for the motors, are setup to be able to handle any tape, at least in both Rewind and fast forward mode(help here, anyone?).

I think these machines must have had a separate filter capacitor for each motor, probably even a dedicated transformer winding. The capacitor could be the problem. what is it, between 2200uF and 5600uF?

I suggest you obtain the service manual, otherwise you're relying on the help of others. It holds all the necessary information for doing what you need to do. And I sure hope someone more knowledgeable than me (about that machine) will answer this thread...

cheers,thumbsup
2N

[Tim Farrant]

This is a common fault with these machines as they age. It may be the driver transistor for the motor has gone leaky, or it may just need a proper alignment of the servo's.

[brianroth]

Originally Posted by Tim Farrant

This is a common fault with these machines as they age. It may be the driver transistor for the motor has gone leaky, or it may just need a proper alignment of the servo's.

Indeed, there are a bunch of trim pots in the servo system, although I don't have a service manual here to reference.

Best,

Bri

[niva]

Wow!

Thanks for all your inputs!

I think I'll begin with baking my 3M 996 as they are quite old but I doubt it would solve the problem: it should behave the same in fast forward, but the machine works as new on this mode.

I've read the service manual but it doesn't say much about tension problem, just the regular tension adjustment. And I did bring the machine for a mechanical tuning a couple of month ago, it is supposed to be perfectly align mechanically.

You can get the service manual here if you want to take a look:

User manual FOSTEX G16S - User guide FOSTEX G16S - SERVICE MANUAL - English - Diplodocs

I guess I should solve the problem quickly as I am scared this could damage the motor in the long run, right?

Thanks again!

G

[2N1305]

Well you can optimize the drive and servo circuit all you want, but if the capacitor is leaky/bad, the motor won't work properly. the service manual is not downloadable, as far as I can tell.

[niva]

Yes it it!

Just click "Download the complete user guide (19301 Ko)" and you'll actually get the SERVICE manual..

Good to know for all G-16S users!thumbsup

Cheers!

[2N1305]

ah, OK, I didn't want to risk downloading such a big file if it wasn't what I was after.

I had to make a bogus review of the thing in order to get it, but I am sure no one really cares for old technology. Except people like me. And you, obviously!

[2N1305]

OK, after a brief investigation of the G16's schematic diagram (of the Power supply section, page 92), I would suggest replacing R13. Or at least measuring it to see if it's still 0,33ohm. There is a good chance it has become more resistive than it should be and is presenting a voltage drop that is affecting the motor's operation. since there are no caps for each motor, I'd say that it isn't a concern anymore. But if you'd like to replace the filtering cap, C1 (is it 5600uF? hard to read), then by all means, it can only help.

But the real problem may lie in the motor itself. These are no doubt brushless DC motors, quite expensive but turn the shaft by hand to see if it turns freely, just as freely as the take up reel shaft.

I've attached a little illustration of where the components are that you should check, if you feel like doing it. Took me quite a while to figure out that there some transistors that were changed(Q5 and Q7 are Q5 on the Regulator-M board), if you look at the schematic and then at the circuit board drawing.

[niva]

First of, I'd like to thank you all for your help. That's one of the reason why I am kind of a forum geek!

Second, I took a look at both motors and it seems indeed that the supply reel table is a little harder to turn (without the reel, obviously). It might explain the difference between both. I increased a little bit the tension on the supply reel with the REWIND TENSION pot and it seems like it works a little better now. But I will only know when my tapes are going to be at their best (baked).

Third: is there a way I could improve the life of the supply wheel motor? There is an small black hexagonal screw holding the reel holder to the reel table, would loosing it help the motor to move more freely? (I don't think so...)

Is there a way to lubricate those motors? I don't think so cause it's not indicated anywhere in the service manual.

I'll check the actual value of the resistor later, just to make sure.

Thanks again for your help!

Guillaume

[2N1305]

Guillaume,
don't loosen that screw-it holds the reel table on the motor shaft. You could (I have time on my hands) take the motor apart and clean it, then lubricate it, essentially making it almost new again. But that will take you about two or three hours.

As far as I understand the circuitry, the tension potentiometer simply varies the pulse width that drives the transistor of each motor. Pulse width modulation is a way of controlling the duty cycle of a given waveform, and is often used to vary the speed of DC motors (like some cordless drills) without changing the voltage or current applied to it, which would reduce its torque. this way the voltage remains constant, it's only that the voltage is applied for a certain time, then is absent. On-off, thousands of times a second.

I could be wrong and the Fostex actually uses some other way of slowing the speed, but I'm pretty sure that's how it was designed.

cheers,

2N

[Radardoug]

I note you are running old tape on this machine. Are you cleaning the machine regularly? You need to clean everything in the tape path scrupulously. It is a common symptom of a dirty machine to be slow in rewind, because often you hit rewind when you are only a small way into the spool. The recomendations are: Clean and demag every 8 hours, or less if the machine usage is heavy. With old tape this drops to clean every run through. Some tapes leave a sticky clear residue, so even if yoy can't see anything on a guide, clean it anyway.

[niva]

Hi guys!

I didn't check the suspect parts, that was a little (just a little) over my technical knowledge and my courage...

Anyways, I tested the rewind again today, as my tapes were baked and it seems like problem was far from being solved...

The problem is, precisely: the rewind function works great on the long run: if you rewind the tape completely, from end to beginning, you won't notice anything wrong... except that it is a little bit slow to reach it's full speed, but once it gets launched, nothing can stop it (dixit, Le petit castor) until the tape gets to it's end...

Here are more details on the laziness of the supply motor on REWIND: if for instance, I am at the beginning of the tape, I RESET the counter, let it run for like 0-7 seconds, then push the "LOCATE 0" button to return to zero, the motor would stay on the idle or barely move... If I help it with my hand, then it would return to zero. If the counter reach about 20 seconds or one minute, then press the "Locate 0", it would return to a couple a "frames" from the zero point... and stay on idle. So I have to push STOP for it to stop completely. If I go further than about a minute, it would reach the zero point quite easily...The problem is less obvious the further the tape goes (as the supply reel has less tape and gets lighter...).

So it seems like the problem is specifically when the motor don't get much power (voltage?): when it goes form stop to rewind, and when it comes from rewind to stop...

For the tape cleanliness of the tape path, I am aware of all that goo stuff than can get on it, and I clean every parts regularly.

So, I took it to my tech and explained the problem in details. It might not be the resistor's fault (R13) as it is acting for both motors, if it was so, the problem would also be for the take-up reel...

Now both of us think it could be that the driver transistor for the motor has gone leaky just like M. Farrant said, or the motor needs to be dismantled, cleaned and lubed, like 2N said. OR the problem could be elsewhere...

What do you think?

I'll keep you updated as I'll get some news from my SUPER GENEROUS AND DEVOTED TECH (he is probably following this tread as well)!

[2N1305]

Well, There is no "single" driver transistor as far as I recall (the schematic is on another computer, I can't recall 100%). There is a driver transistor for each motor. The only Common elements for both motors is the power supply, consisting of, if I recall:
-the transformer (duh)
-the bridge rectifier (I doubt that would be the problem) -the capacitor (remember I said change that it's under 15$ and it's due)
-a "bleeder" resistor, in parallel with that capacitor. Could be going down in value.

I much rather think it's R13 and it's cousin in the take-up side, or both driver transistors, if the problem is there on both Fast-Forward and Rewind. But the Cap is my suspicion. Just measure the voltage, check the manual and that, in an instant, will tell you. Better yet, plug an oscilloscope on that supply and check the ripple, I don't think you should have more than, ah I don't know, 3V of ripple, peak-to-peak?

dam, I want that machine here ON MY BENCH!

2N

[Radardoug]

Hi, Good to hear you are cleaning regularly. Try this. Put machine in rewind. apply slight downward pressure to the tension sense arm on the supply side. Does the machine accelerate? If this does not work, try slight upward pressure on the takeup side tension sense arm. This is a way of checking the reel servos on each side. When you change modes (rewind, play, fast forward,) you should see these arms move if the reel servos are working.

[niva]

Ok guys.

I had the Fostex G-16S checked by my tech today... And it seems like all voltages are perfect everywhere. All the resistances are good and the driver transistors too.

Now there is only one (or others?) solution left: refurbishing the motor. Also the take-up reel has a little up and down loose on the shaft... Porbably the shaft's bushing is kind of short...

Do you know if it is risky to have the motor dismantled?

Do you know where I could find replacement parts for these?

My tech sees no problem dismantling them, but as he said: this operation could make situation even worst if there are some inner parts that cannot be found...

Do you know where I could find replacement parts for these?

Anyone ever did that?

Thanks for your help once again!

Guillaume

[Radardoug]

Have you tried your local Fostex agent? Or done a search for the part number on the web? the other alternative is take it to a motor rewinder or auto electrician, they do bigger motors but might be able to do it.

[brianroth]

I also assume that the mechanical brakes on both spooling motors are fully releasing. A dragging brake band can cause the same symptom.

Best,

Bri

[2N1305]

Originally Posted by brianroth

I also assume that the mechanical brakes on both spooling motors are fully releasing. A dragging brake band can cause the same symptom.

Best,

Bri

Damn, I should have thought of that. Guillaume check that (your tech) it'll be a real saver if that's all it is!

[Tim Farrant]

I don't think the G-16 has brake bands, does it? I don't ever recall seeing them in these machines, been a while but....

[brianroth]

Dear Tim,

Like every servo-controlled transport I can think of, I'm almost positive the Fostex has them as "failsafe" in case of an AC mains power outage.

Best,

Bri

[2N1305]

Originally Posted by Tim Farrant

I don't think the G-16 has brake bands, does it? I don't ever recall seeing them in these machines, been a while but....

Well how else would it brake?

Oh, resistor braking.. yeah. Well, could be. But i would have noticed in the manual. Or maybe I didn't... whatever.

[Tim Farrant]

DC motors, not ac motors, so under servo control. If you recall they took quite a while to actually stop from spooling speed when you hit the stop button!

[2N1305]

what exactly is meant by servo control? Obviously this thing doesn't use dynamic braking like the old Crowns...

[niva]

Hi guys!

I have good news!

The motors (DC with inner brake bands) had been dismantled and cleaned. Apparently, they were almost like new, with brass brushes still in good shape. The loose on the take up reel was caused by a loose screw... And that also explains why this motor was easier to move than the other one...

So now, they are equal and BOTH have a little difficulty with the "Locate 0" function when tape is close to that "0" point...

So, the source of the problem boils down to....

THE TAPE ITSELF (old but not-so-used-and-baked 3M 996)!

M. Eddie Ciletti in his delicious "Analog tape 101" series of article says:

"I do not recommend using high-output tape on narrow-format machines. Mechanically, they are heavier, less pliable and more likely to accelerate headwear. In their heyday, Tascam’s MS-16 and Model 38 would become sluggish over time using the recommended tape (Ampex 456, 3M 226). Having the reel motors rebuilt will improve performances and extend the life of the motor drive amplifiers. Electronically, some narrow-format machines are not capable of full erasure. Also, as some machines absolutely must be run with the built-in noise reduction, there really is no need or no point to pushing the levels."

So, as it appears that the old 996 has a tendency to stick on the reel (even if baked), I think, I'll get a fresh roll of RMGI 911(still a high output tape since it is the equivalent of Ampex 456?) and see what will happen.

For your information, here is the thickness difference of the tapes I am planning to use:

3M 996 (only with my Otari MX-5050 MKiii 8 track): 2.13 mils
RMGI 900: 2.05 mils
RMGI 911: 1.97 mils

Is the difference in thickness that significant?

Thanks for any information!

Guillaume

[2N1305]

Hi Guillaume,

indeed that is good news! Kinda weird, but good! I never would have believed it, but having it come from Mr Ciletti Himself (I knew about his website and professional experience), then well, it must be true! It looks as though he knows this from personal experience so I cannot argue with that.

I do find it surprising, however, as I said to you, the thicker the tape, the heavier it is (for equal lengths). Also the fact that it is a high-output tape mus account for something else too, like magnetic flux. Although I would believe this to be more problematic at High speeds, not when it's starting up, since when it's starting up, there is no magnetic field to break, since the tape is not in motion. I might not be making sense here. Homer without beer not well talk without.

Well, as long as you can record, you'll be on your way!

how 'bout them pictures?

cheers,

2N

[2N1305]

Originally Posted by niva

...
3M 996 (only with my Otari MX-5050 MKiii 8 track): 2.13 mils
RMGI 900: 2.05 mils
RMGI 911: 1.97 mils

Is the difference in thickness that significant?

Thanks for any information!

Guillaume

I don't know... it is 8% thicker, therefore 8% heavier. Let's say your roll of 996 weighs 4lbs. (I 'm just guessing here) well, 991 weighs 3,96lbs. Heck, that's like four peanuts! I don't get it...


I think the difference lies in the fact that the tape sticks to the damn heads because it is more abrasive due to the fact that it is more metal. (iron particles) More metal?

How bout some Judas Priest?

[niva]

Hello guys!

I got some (good) news!

I finally got 2 fresh reels of RMGI 911 and tried the machine with one of them... The problem was still there, although it was a bit better than before, but still, the motor was idling just a few frames before the zero point. But then, I realized that the first roller below the take-up reel was kind of sticky... even though I had cleaned every part of the path with head cleaner.

The thing is that THE HEAD CLEANER WASN'T STRONG ENOUGH to take off all the gunk. So I took some car paint lacquer thinner and thoroughly cleaned the tape path once again and TADAM!!!

So now, my Fostex G-16s just need to be calibrated and then, it will be ready to be rocked and rolled!


Just wanted to share this with you guys.

Thanks a lot for your help once again!

Guillaume

[2N1305]

Bravo Guillaume,
content d'ent...
I mean: Happy to hear that!

That take-up roller must drive some kind of optical slotted wheel that in turn goes to the microprocessor. It must have been thinking, ah, we're getting near the end of the tape, better slow down... Or something like that.

anyway, we're all eager to hear some for your stuff. Well, I am...

take a look at my latest post if you want to see what I was working on. Might take me another 19 years...

[imaverysoundman]

hey slutz...
just pulled out my old fostex g16s out and am trying to get it integrated into my system....only used it once about 10 years ago....it seems to be working ok..am having a similar problem like you had with the play button taking a while to get going sometimes...but the main reason im posting is that i cant seem to get any input or output levels on the meters....it used to work..im wondering if you have any advice on that...i have both manuals and am doing what they advise but no signal seems present although it is playing back...(but with no levels present)......any thoughts??
cheers
tris....