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RT-701 Wobble and Rumble?

JoshuaZ

JoshuaZ

New Member
I picked up a very dirty but seemingly fully working RT-701 for $50 the other day. With some clean up it'll look fantastic sitting next to my SX-1050 and PL-570. However......

Everything seems to work electronically but the left motor has a slightly wobble and slight audible rumble to it. I took off the spindle lock and it looks like that little screw (that the small spring goes over) is bent a bit at the end (maybe 10-15 degrees along there threads). Even with the Spindle lock off there is most certainly a slight wobble and rumble from the left motor. There is no such rumble on the right side.

Is a slight wobble normal? (Since I don't plan on doing much reel to reel, I can live with imperfection)
Is this something I can possibly adjust on my own, and if so how?
Is this something that would require a new motor or other part to fix up? (Maybe a new spindle assembly?)
 
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Hi JoshuaZ,

Bad luck there, I'm afraid!!

If the shaft of the motor is bent in any way, this will cause 3 big issues with little ones besides.

1. The sintered sleeve bearings for the shaft will be damaged. This will reduced the life of the motor severely in what ever state it can manage at his time.

2. If the brake hub is eccentric then the brake torque will be unstable. This will get the tensioners wagging during a stop from a fast wind as an indication of the severity.

3. The torque from the motor itself will also be modulated and may/will affect the tape path across the heads. The Wow/Flutter figures will probably be unachievable. This may/will also affect the high frequency response of the machine as the movement of the tape will be affecting the Azimuth. If the tape wanders up and down the limits of the tape guides there will be a corresponding angle superimposed on the tape path to allow it to do so.

These issues will be an annoyance during playback and will ruin every recording done on the machine until the fault has been rectified. You will need to keep an eye on a certain auction site and see if a machine has been broken for parts to get a replacement motor.

Even if the shaft could be straightened, which I doubt, the damage to the sleeve bearings has been done!!

One you have heard it running you may feel a replacement LHS Motor is justified. They are cracking machines and perform very well indeed!!

Cheers.

GPS16
 
Oh drat, I was afraid of that. Hmm.. looks like I'll have to keep an eye out on eBay for one then. Thanks!
 
GPS is right. You need a motor from a parts unit. They do come up. You can flag the Ebay to send you an email whenever RT-701 or RT-707 comes up, and scan those for indications of a unit being parted out. You could also subscribe here at AK ($25 per year), and post a WTB ad (Want to Buy). Maybe one of the members has a parts unit to draw from. Don't try to seek such in the regular AK forums, as that is not allowed. We have a special area, called BarterTown, visible to subscribers, where that kind of thing can be done.

Good luck,
Rich P
 
Looking at the service manual the hub/motor assembly looks very similar to professional Studer Reel to Reel players in that the spindle isn't the motor shaft or attached directly to it. I guess it all depends on what is off-center. If the spindle is off-center, but the reel-base it's mounted to is centered, you may be able to replace just the spindle, or just the reel-base it's attached to if it's off-center. Cintered bearings can be difficult to work with. Studer requires they be sent in for repair, where they are perfectly matched to to the motor shafts and run in for 24-hrs. They then check the union of shaft and bearing for heat caused by friction. There is a service manual available on HiFi Engine.
 
JoshuaZ said:
As much as I'd love to have someone else work on it, that's outside my budget.
Click to expand...

My intent on posting that website wasn't to convince you to send it to that place for a repair.

I was basically letting you know of a place that not only repairs but sell's reel to reel parts, that is if you were planning on performing the repair(s) yourself.
 
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