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Having an issue with rewind when using a large reel. It starts out rewinding ok but as the reel fills up it slows and almost stops. Works ok with a 7" reel.
Would anyone be able to point me in the direction to fix it , I'm not sure what could cause this.
These machines are not the normal-type of RTR, with AC motors, and resistors to regulate the rewind/fast-forward. They use brushless DC motors, all three, and use full logic to rewind/fast forward. I suggest you have a problem caused by bad electrolytic caps, (VERY common with these machines, and virtually all 30-plus year old machines) or a logic circuit problem.
GREAT RTR's, (I own one) Get it fixed! Your best bet is a tech on Tapeheads, there are several very good techs there.
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I'm sure your problem has come up before and been discussed on tapeheads.net or the Yahoo reel-to-reel group, or both.
+1 on that. I'm a member on tapeheads.net, but I rarely chime in there, 'cause I'm lazy.
Edit: I'll take this opportunity to reiterate that, given your info so far, the first place you should look is the back-tension on the right reel side.
Here are results.
Tape paths are all clean.
It rewinds ok on 10" reels with about 80% fill. Full reels cause the problem.
Bearings on dancers spin free.
Tension is same with only NAB hubs.
When coaxed into FF the left hub can be stopped and moved easily both ways.
A full reel rewinds nicely on the left side with nothing else attached.
It used to rewind full reels but stopped doing it about a year ago, I have a crown machine that will rewind them in a flash.
Have always wanted to fix it.
Seems like it has lost the grunt it once had.
"A full reel rewinds nicely on the left side with nothing else attached."
So, it spins fast and good all by itself, with a full reel of tape?
Then, we're probably looking at a back-tension issue on the right side. This can either be mechanical, or electronic sensing. Either one can be easy or expensive to fix, depending on whether it's just an adjustment or if it needs new parts.
Yes, the left reel when full will spin fine alone. But when a full reel is hooked up to the right side it starts to slow dramatically when about 60% of the reel is rewound.
Put 80% full reel on and it rewinds fine, doesn't slow down at all.
Ok. Then, you're "probably" looking at a right/take-up reel back-tension control problem.
"Back-tension" is applied to ensure that there is appropriate tape tension in order to avoid "spillage", particularly when fast forwarding or rewinding and then hitting "Stop". After all, we don't want tape all over the floor, do we?
I can't help you beyond this, since I'm not familiar with that particular machine, except to say that you might try using an almost fully loaded "junk" 10" reel of tape on the right/take-up and see what happens when you do some testing in the FF mode.
Heck, use a junk tape and try it "six ways to Sunday".
you had it serviced? Have the caps on the logic board been replaced at all? Perhaps it is time for a full restoration such as a full recap and replaced the brakes.
The moving parts of these machines can only last for so long especially the motors.
Good luck in finding a competent tech to do the restoration for you.
If a thing's worth doing, it's worth doing well
I'd double check all the multipin connectors by pulling them and reinserting, adjust the reel tensions and make sure the brake isn't dragging.
Past that, it's time to check voltages. Maybe pull the motor, clean and lube.
This post has been edited by the author.
Large reels on BOTH sides? Same problem in both FF and Rewind?
Are the bearings on the "dancers" (on either sided near the top of the headblock) binding up?
To check if brake pads retract from reel when moving tape. Put on just NAB adapters with no tape. Spin them back and forth - is the "tension" roughly equal for both in each direction. While holding down both tape dancers, push FF - The left (supply side) adapter will spin a little but can be stopped with your hand - spin it both CW and CCW - if the brakes have retracted, the relative "tension" should be less than when the reels are not turning. Try the same with Rewind on the right side shaft/adapter.
FWIW, the "brakes" on the 1500 are nowhere near as "clamping" (not band brakes) as on other machines.
Also be sure that all the tape paths are clean - could be gunk on a non-rotation surface.
Is the tape on the 10" reek Ampex/Quantegy 456 by any chance?
Even if it isn't, there's a good chance that it has sticky shed syndrome and it's stopping the transport.
Try a "new" tape or if you have one, one that isn't back coated.
And like Charlie said (hey Charlie) clean the tape path.
That's a valid question, Ironbut. I tend to think that's not the problem, but rather a mechanical/logic problem regarding the right side/take-up side of the transport. This is because the problem doesn't manifest with 7" reels. On the other hand, the 7" reels may be an entirely different tape, but we don't know that - yet. This is just ONE of the problems with diagnosing over the Internet! :)
My first recommendation to the OP will eliminate the left reel motor as the issue, and then we can address other issues.
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