RT-909 ff rewind slow and then stops

This is a new-to-me reel to reel (the military version, 1 fuse). So far I've replaced the belt and had the pinch rollers rebuilt. I then rebuilt the tensioners replacing the microswitches, etc. I then recapped the Counter Assy board (3 caps). I then replaced the 1 amp (blown) slow blow fuse that someone had installed with the correct 2 amp fast blow fuse. Hooked it up to my dbt and it failed. I then recapped the Control B Assy board (C223 was shorted). It passed the dbt test so I plugged it in. Today I installed a tape for the first time and gave it a try. It was recorded at 3 ¾ so while it worked it sounded like chipmunks. Forward and reverse play worked, as did FF. FF rewind on the other hand started off significantly slower and eventually came to a stop. I’ve read in another thread that fast modes that start fast, then slow at the end are generally due to incorrect balance between FF/REW torque, and back torque, as well as incorrect selection of reel size (or bad selection circuitry). Any idea as to what to look for? Continue recapping?

Never worked on one of those but have seen similar symptoms caused by misthreading which can be caused by the pinch assembly being sticky with dried grease. If it does not move all the way to the stop position there might be a finger type tape guide that is only supposed to stick out when NOT in play mode. If it has a cue function, that is what it moves so the tape is audible in FF, REW and pause for editing. Actually for marking foe cutting and splicing.

the unit will usually play and record fin like this, but the tape being behind that "finger" instead of in front of it cuases alor of drag which will load the reel motors too much.

And I am PRETTY SURE that unit uses separate eddy current reel motors. It is unlikely for both of them to go bad. Also, it could be a problem with the brakes or tension bands not working properly. Tape tension is the way to figurre this out.

Your finger is the tool. In rewind, if there is tension between the suply reel (left) and the heads, then check to see if there is tension between the takeup (right) reel. Then you know if the excessive tension is coming from the takeup reel brake or the head assembly.

If there is no significant tension and the torque is lkow from both reel otors, it is probably an electronic problem. I think the engine has the print. If it is affecting both reel motors I would seriously suspect a low supply voltage, possibly due to a filter cap with high ESR, or something like that.

Many units do regulate tape tension even in fast wind, so really, those arms all have to be working right. they also have to be threaded right. I have seen people make that mistake, if the tape is not pulling that arm, there will be too much tension.

Go from there.

How's the pinch roller BTW ? I hear those turn into mush. In fact, maybe it did, and even if it was changed it may have left some sticky stuff somewhere in there which is not apparent.

That's the possibilities as I see them.

This happens if the tape you are using is old and sheds oxide. Check the tape path, is it it still clean after running the tape through it? This is called SSS Sticky Shed Syndrome. Of course there could be another cause as well.

DeOxit the reel size control. Then adjust all of your reel torques to spec. Likely, the fast mode back torque is too high and/or the fast mode takeup torque is too low. The deck will be more sensitive to these issues with large reels.

When you adjust the reel torques, do them all. Then, do them all again, and repeat until you can make a complete pass through the settings and not have to tweak one. Tend toward the low end of the range for back torque, and toward the high end of the range for takeup.

Don't mess with the torque pots without the proper ability to gauge/measure the results. Be prepared to replace the pots. Do not try to DeOxit them. If one is bad, replace them all.

Good luck,
Rich P

I had the tape threaded incorrectly. I wasn't clear from the owner's manual but I found a youtube video that made it obvious I didn't have the tape correctly threaded in the area of the pinch rollers. Thanks for all the help, I truly appreciate it!

Still, even with a finger, check the torque. Or a stick.

Like the others mentioned, it needs to have the right rorque for tape nadling. What's more alot of older tape sheds not only oxide, but it seems glue as well. It gets sticky.

One thing, after you use a finger to make sure it is not stretching the tape via the reels, make sure there is not alot of tape tension between the capstan and the heads. Dirty heads cause alot of drag these days with that goop coming off the tapes. Always be on the watch for that if you intend to use R2R these days.

BTW, to those who talked about setting measuroing the reel torque, what do you use ? I remember a device I think was called a tentelometer or something like that which had three fingers and measured tape tension quite accurately. Of course the manufacturer might not use that number, but the optimum number could be figured out. (actualy that can also depend on tape thickness)

Anyway, I like R2R but have not persued getting a really good one because of the cost of tapes. And actually, if someone has tape and reels for a ½" 8 track machine I owuld be interested. Tape is the biggest problem. I tried using VHS tape but couldn't make it work right. And my buddy has NOS Ampex tape that sheds like a long haired dog, WITH STICKY OOOP ! Never been out of the inner bag but totally bad. I guess it just happens.

I got a spring scale set like this one to do my 909 (among others):
http://www.teachersource.com/product/139/lab-equipment?gclid=CPPWxfO0xsYCFdAXHwodiksBTw

It's been a while since I've done mine, but I think the instructions are very explicit on how to set all the torque values using spring scales.

Good luck
Glenn

Thanks for the info! I have a 0 to 500 g force gauge I can use. From the manual all readings should be in that range. Should I replace VR 201 through VR210 while I’m recapping? If so, does anyone have a list of replacements I can use?