hifi engine

RT-909 tape path problem

I have a Pioneer RT-909, everything works well except that the tape wants to climb off the pinch rollers. As the tape plays it gradually slips inward toward the machine. It seems like the tape path may not be in alignment. I have the owners manual, and a copy of the repair manual. The only adjustments that look like they might fix this are, 1) adjusting the reel base heights, or, 2) adjusting the pinch roller pressure. Does anyone have aby suggestions about what else might fix this problem? The pinch rollers are in good shape and fairly new.



Re: RT-909 tape path problem

I've had the tape mistrack issue several times on dual as well as single capstan machines. Pinch roller to capstan grip of tape is important. On dual capstans supply reel back tension is less of an issue, but you'll need a spring scale to adjust it, not a digital scale. Apply a little extra drag with your finger on supply reel to see what happens. Try playing tape from right to left and see if you get better results. Sometimes it's the tape itself. Make sure you have the slip washers on front and back of pinch rollers so the roller doesn't creep. I have a work around if those are missing. Check as best as you can that pinch roller to capstan is parallel, after decades of pressure in the same direction, this may be an issue too. But start bending things only as a last resort. Grab the flywheel in the back and check the bearing for vertical free play too. The capstan shaft is tougher than the bearing is.

Re: RT-909 tape path problem

bobkeller, it turned out to be the slip washers. I guess I had forgotten to replace the outside ones when I replaced the pinch rollers. I found the washers in the box of misc 909 parts I had in my desk. I replaced them and the machine works like a charm. Thanks so much for you help.

Re: RT-909 tape path problem

Thanks, bobkeller for your response. I am leaning toward the pinch roller to capstan grip. I cleaned them both very thoroughly yesterday, and the tape played fine for a while, then it started creeping again. The other possibility is the slip washers, I'm not sure if they were reinstalled correctly when I replaced the pich rollers. I'll take them apart and check, but I'm not entirely certain how many there are supposed to be. I'll also try and check the pinch roller to capstan surface orientation to see that they are truly parallel. The tape creep occurs when it is played in either direction, but it only occurs with one of the pinch rollers. I will also check the flywheel. Thanks agin for your advice. And thanks to everyone else for their advice, too. I'll keep you all informed. I have another 909 sitting in my workshop with a blown output transistor on the right channel. It was working fine until the transistor blew, and I think it took a couple of other components with it, I haven't had the time to check it out yet. Mechanically though it seems to work fine.

Re: RT-909 tape path problem

The following steps are only "if" a new belt was recently installed....

1.) Was the belt recently replaced? If so was it the correct one and or exact size? If not then this could very well be the problem?

2.) If the new belt was the correct one or exact size, then were the surface's of both spindles that the belt goes around that drives the tape, cleaned real good? No left over residue from the old belt? If not cleaned real good to the point that nothing was left on them, then fine but if not then if any particals left over from the old belt is on them then this could cause the belt to not function properly which was intended for?

3.) If new belt was correct size and surface spindles cleaned, then was the 'capstan's pully' installed correctly? That is, when the capstan pully was reinstalled it was installed with the pully resting on top of the belt for proper tension? Not underneath the belt? If installed underneath, there would be some tension for the belt to move but just not correctly and this would definitely cause problems?

4.) Was the 'tape path' cleaned real good? Meaning, there was absolutely no residue or particals left on any of the heads or any other part that the tape runs through or touches? This would also definitely effect the performance of the tape when played?

5.) Finally, if all four first steps were accomplished then start looking at adjustments for the tension areas, etc.

Re: RT-909 tape path problem

As I replied to johnnysan, I did recently replace the belt. I got it from a reputable source, and changed out the pinch rollers at the same time. I did clean the entire belt path, but will check it again to make sure. I will check the capstan pulley, too. I'm pretty sure that I replaced it positioned it correclty, the replacement belt and pinch rollers came with detailed instructions on how to replace them. I also carefully cleaned the tape path, but I did notice that there is some wear on the heads with obvious "channelling" where the tape has passed over them for years. I know there is a service place that will resurface the heads for a fee, and I might look into that. The deck did work fine for a while after replacing the belt and rollers.

Re: RT-909 tape path problem

Did you replace the belt? Did you clean off the old lubrication and replace it? How old is 'fairly new'?

Your reel table height should not change by itself. The pinch roller pressure shouldn't change much either.

Your tape tension (back tension and take-up tension) may be a problem. You will need special equipment to properly test this.

Re: RT-909 tape path problem

I did replace the belt just a little while ago. I thought that I had cleaned the entire belt path thoroughly but I will check it to make sure. At the same time I replaced the belt, I replaced the rubber pinch rollers with new ones bought from a reputable source, the same place I got the belt. The pinch rollers on the machine were in pretty bad shape. They weren't goo like so many are, but instead had become hardened. They machine worked fine for quite a while before this current problem popped up. I did adjust the table height slightly on one of the spindles because the tape was consistently rubbing on the plastic reel.

Re: RT-909 tape path problem

I recently did some work on a RT707, which is very similar, and has the same 3 motor transport.
I found that I had to adjust the reel tension for both take up and supply, to correct a similar problem where the tape was almost pulling off the capstan on startup. The take up reel tension is set by adjusting the adjustable high power resistor located near the take up motor. On the one I worked on, the take up tension was way too high. I set the resistor so that the tension was reduced, and the tape problem went away.
Tom