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Fostex G16.....another strange rewind issue
Old 7th September 2018
  #1
Here for the gear
 

Fostex G16.....another strange rewind issue

Hi!
I bought a second hand G16 Dolby C version, and it had the typical slow rewind problem. So i decided to clean the reel motors. A lot of carbon was inside, so i reassembled them after cleaning, and looks like the torque issue is solved. BUT.......when i press rewind button, now is the same as FFWD! Of course it worked as supposed before, rewinding instead of FFWDing.
And in the play mode, looks like the motors don't respond to the tension sensors..... So when i press play, looks like both motors run slower than they are supposed to run, making the tension arms going down, so the machine stops.
Any clue??
Thanks in advance and hope my english grammar is getting better!
Old 10th September 2018
  #2
Lives for gear
 

That recorder uses friction breaks which put drag on the hubs so the tape winds properly.

Fast forwarding and rewinding require the pull and the drag to be properly balanced. If the breaks have too little drag the tape will spin too fast and free wheel when stop is selected and tap would flay off the reel all over the place.

Too much drag and the break system winds up burning up your feed components, motors, belts etc.

What it sounds like from your description, you cleaned your break system and it put way too much drag on your feed system.
This is a problem when you get people screwing around with gear when they don't understand how it even works.
Just because something is black and ugly doesn't mean that stuff isn't "supposed" to be that way

What you'll need to do now, is rebalance your breaks to produce the proper tension. too much drag you burn up your feed components and wear the heads out. Too little its going to jam like crazy and not provide enough head tension.

My advice is if you have a pro in your area get him to do this work for you. Believe me when I tell you. if you screw these adjustments up you may as well take that deck down to the dock and tie it to the boat anchor chain. it taint never gonna run right if you don't get the break drag right.

Normally this adjustment is done when the breaks are new. You then run the unit till the breaks fail then simply change the breaks so you don't have to tweak the adjustments in between. You've monkeyed with the break system with worn breaks and it seems that the break surfaces grip way too much now.
A pro would recommend replacing the breaks now, not simply adjusting them to reduce the drag. Unless you are a pro at tweaking them, you'd need to reduce drag now which could lead to having too little drag shortly afterwards as the belts begin to glaze again.

Nest solution, replace the breaks now, if they are available, then set the proper tensions, then keep your hands off the thing till they need replacement again.
There are parts in decks that can be cleaned and oiled on an ongoing basis. There are others designed to be maintenance free and are supposed to be run until they fail. You've discovered the ones you shouldn't have messed with and your efforts to clean things and make it better have created the polar opposite.
As a tech I'd need to see how badly the break belts are worn. If they were at half life I might try adding some slippage using an extremely small amount of dry lubricant like graphite to get some slippage back. Normally these belts have a felt coating so they slide smoothly on metal. Once that felt wears off it gets down to flat cloth or rubber and grips too much. Add a small amount of lubricant is very risky because you can wind up having the complete opposite effect.

As a tech I used to do allot of that stuff on decks because parts were obsolete and you had no other options besides keep it limping along or fabricating your own parts (which I became quite expert at too) If you can find the break belts I'd suggest you fix the deck using them first. If you can even find them thay are a key component you want to buy an extra set too, because you wont be able to get them for long.

After changing the breaks then you may wind up needing to change your drive components too. Both the break and drive components are designed to be changed after so many hours of use. They are all designed to be changed together so you get even wear. When you interrupt that cycle even if its with good intensions like you have, you have few options to fixing the problem. Again, I cant see what kind of wear there is, if I did I could tell you very quickly where you stand. It takes allot of first hand experience to know if there is still life there but when in doubt, its better to do the work right and simply replace the components.

Once repaired, take the lesson you've learned here and keep you hands out of the gear. You'll never see the insides of enough of these units on a daily basis owning one unit. Techs who do the work for a living see failures on a daily basis and can make the call between salvaging what will work and what wont. Just realize, the techs who repair these units are as rare as good running decks are any more. I'm 61 and got into repairing them professionally late in the game. I was good at it because I started back in the 60's as a kid but once my generation of techs is gone you can kiss off any professional repair.

There is a manual here is you want to brush up on what's involved. Fostex G24S Service Manual (Page 9 of 98) The theory/adjustments for this problem begin around page 6. The break uses a spring to add pressure so there really isn't any adjustments besides reducing spring tension which I wouldn't advise. You either reduce friction by making the hub slipperier or you replace the belts and increase tape pull on the feed side. Much of that requires checking speeds with a scope and there is nothing an amateur can do besides make sure the idler is clean. I cant see by the manual but it looks like it might be direct drive like my old Teac's are. If so you don't have allot of mechanical adjustments there.
Old 24th September 2018
  #3
Here for the gear
 

Thanks for your explanation wrgkmc, really crystal clear, but haven't touched the break system. I know about such issues dealing with the break system if not needed, have restored successfully several tape machines. And i dont have any qualified technician around here. And most important thing, as there are not many technicians as you said, i want to learn.
What I was talking about in my description of cleaning the motors, is that I cleaned the carbon from the brushes inside the motors, and checked the brushes, maybe they needed replacement. But the brushes can work for some years yet.
I guess is something with the servo circuit, because now the take up motor runs reversed, changed one motor by the another, and in the take up servo circuit both run reversed.
Old 24th September 2018
  #4
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Radardoug's Avatar
 

You might have re-assembled it backwards, or wired it up backwards. These are d.c. motors, the direction of rotation is controlled by how you wire it to the supply.
Old 4 weeks ago
  #5
Here for the gear
 

The motors problem is solved, just bought two and now works!!

BUT.......the typical problem with lazy motors on this machines.........
After installing the new motors, rewind worked as expected, i was using it during a day, so it looked solved. But suddenly the next day, the lazy motors came again.

Just check your batteries. I removed the batteries as i thought something has changed something on configuration, and suddenly the machine worked as its supposed to be. So a new trip to the shop, bought some batteries, and the lazy motors problem is gone!!

Hope this helps to everybody who is suffering this annoying problem.
Old 3 weeks ago
  #6
I had one of those machines with the autolocator years ago. I loved that deck.
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