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Pioneer RT-909 no control after FF or RW

K

kanurys

Active Member
This RT-909 will play in forwards and reverse from a stopped state. In Play mode it will stop when the stop button is pressed.

The Problem:
When Fast Forward or Rewind is pressed the unit spins up in the appropriate direction. The only signal that will stop the FF or RW modes is when the tension switches close. While it is in FF or RW none of the control switches (FF, RW, Stop, Pause, Play Forward, Play Reverse) have any effect on tape movement. The green play direction arrows in the button caps do light when pressed, but the player continues to spin in FF or RW.

I've looked at the messy schematic and it seems that the indicator LED's are working, showing me that the IC505 and IC504 are probably working. I suspect the problem to be a failed component related to the stop function or downstream in the controls section, somewhere. Any help diagnosing this would be greatly appreciated.

Schematic:
https://www.hifiengine.com/manual_library/pioneer/rt-909.shtml
 
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Caveat for understanding: The RT-909 employs tape handling that professional operators employ with other machines, except that it is built in with the 909. When stopping the tape from a fast mode, the unit first uses reverse reel torque, until the reels come to near stop (sensed by the counter circuitry). Once brought to near stop with reverse motor torque, the brakes are dropped, unless one or more tape presence sensor switches indicate that the tape has run out, at which time, the brakes are immediately dropped.

Now, if there is no tape installed, the unit will not stop the reels from a FF or REW mode unless the left reel can be slowed to near stop. This is not recommended to be attempted with the hands or other method. Just release a tape presense sensor (in the tension rollers).

If there is tape installed and the described symptoms occur, the problem will likely be in the circuitry or logic associated with indicating left side reel speed (tape counter, etc.).

Good luck,
Rich P
 
pustelniakr said:
Caveat for understanding: The RT-909 employs tape handling that professional operators employ with other machines, except that it is built in with the 909. When stopping the tape from a fast mode, the unit first uses reverse reel torque, until the reels come to near stop (sensed by the counter circuitry). Once brought to near stop with reverse motor torque, the brakes are dropped, unless one or more tape presence sensor switches indicate that the tape has run out, at which time, the brakes are immediately dropped.

Now, if there is no tape installed, the unit will not stop the reels from a FF or REW mode unless the left reel can be slowed to near stop. This is not recommended to be attempted with the hands or other method. Just release a tape presense sensor (in the tension rollers).

If there is tape installed and the described symptoms occur, the problem will likely be in the circuitry or logic associated with indicating left side reel speed (tape counter, etc.).

Good luck,
Rich P
Click to expand...

Thanks Rich. That makes sense. This may point to an issue with the amount of reverse torque applied when stopping. I'll investigate further.
 
10" Reels, tape installed: Could be torque settings, but not likely, by your description of issues. You might try doing it the old fashion way. From one fast mode switch to the other direction. When near stop, hit stop. If it drops the brakes, the motion sensing works. If it does not immediately start to slow down when dictating a reversal in direction, there is a motion control logic issue.

No tape installed (empty 10" reels): From stop, to FF, the right reel should have good strong torque, while the left reel should have very light torque. From stop to REW the opposite should be true. If you go from stop to FF, you should be able to easily hold the left reel in a stop. From there, if you switch to REW, you should feel the left reel want to take off. The same should be true from stop to REW then going to FF, just different reels.

No Tape installed (empty 10" reels): From stop to FF, you should again be easily able to hold the left reel at a stop. If you then hit stop, it should immediately drop the brakes, since the left reel is not spinning. That will indicate that at least part of the tape handling logic is functional.

If the problem is reel torque(s), you will need proper fish scales to set them, per service manual methods and levels. Reverse stopping torque is simply full fast mode torque in the opposite direction, while the other reel drops to light back torque. Not true? You have a control logic issue and a direction to troubleshoot.

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Rich P
 
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From your description and the service manual discussion, the controls seem to be working just fine. I was not loading and rotating the left reel motor properly. The tape tension micro switches are also working just fine.

After that was sorted, I found a new problem: The capstan motor was not spinning in either direction. The pinch rollers were stuck, causing high load on the driving transistors of the capstan motor. I verified that the motor was ok. Then I tested Q210, Q211, Q212 and Q213. I found that Q212 and Q213 were open between the emitter and collector. I will replace all of these driver transistors just to be safe.

The service manual (p. 61) says these are 2SB682. What is a good substitute for these?
 
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