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Pioneer RT-909 Speed Problem

RE-RT909

RE-RT909

New Member
Hello,

my name is Rolf. I am from Germany near Munich. So my english is not very well.

This threat is awesome. Much information about the RT-909. There is no comparable threat in Germany.

I got a RT 909 from a friend. He bought it himself in 1979. This machine was almost never used. There were only 3 tapes recorded. Not used since 1981.

After the usual cleaning and replacement of the capstan belt and the pinch rollers, as well as the overtaking of the mechanics, the machine worked relatively well for a few weeks. The electronic is original. No potentiometers twisted. No screws adjusted. No caps replaced. The sound is still ok. I can compare the sound to a REVOX B77 reel to reel from 1980. This machine has been completely revised by a very good technician. Better than new. And the sound from the RT 909 is nearby.


Now the problem: The band speed varies. Only in 19 speed. I measured the voltage from the Capstan Motor Control Assembly. 24 volts is ok. At pin 9 should be 13.5 volts. This comes from Control B Assembly Pin 28
This voltage varies very much, from 13V to 2V, sometimes 0V

I think the problem is with Control B Assembly in Q212 and Q213.

Does anyone know a solution. I am not an expert in electronics. Which replacement transistors can I use?

I would be happy if someone could help me.

Rolf
 
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My guess: dirty speed control switch. With power off, actuate the switch 50 times, slowly, and see if the problem improves.

Rich P
 
Hi Rich,
Thank you for your quick response.

I dismantled the machine to get to the RWS-079 Switch Assembly. That was not easy. I have measured the switches and they seem to be ok. After that, I cleaned the switches. Before I assemble the machine, I wait for the capacitors I ordered. Otherwise I will have to disassemble it again. I report afterwards. That will take a few days.

What do you think about the heads. Are they ok?

many thanks and a nice day
 

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The head wear does not look too bad, but it is hard to tell. There is some wear, so you should not move the heads, or the edges of the wear grooves will damage tapes.

Enjoy,
Rich P
 
Hi Alain,
Not yet. I'm waiting for the caps. I ordered from Mouser USA. Not all Nichicons can be bought in Germany.
This will take some time. The delivery will come tomorrow.

The machine is disassembled. I will start next weekend.
I will report here what happens.

Nice Day
Rolf
 
Hallo,

I'm just changing the capacitors. There are some other capacitors installed as shown in the circuit diagram. For example on Control A Assembly the capacitor C510. Installed was a 470 uF and the schematic shows a 100 uF.

On the mother assembly the capacitor C902. A 10 uF capacitor was installed and the circuit diagram shows a 100 uF.

Confused. What should I install?

Regards
Rolf
 
Modifications were common during the production run of various models. Unless the installed part looks like a kludge, replace parts with what are there now.

Rich P
 
Hello,

Now I have assembled the machine again. The problem 19 Speed is still there.

I've swapped the capacitors on Mother Assembly, Capstan Motor Control Assembly, Drive Assembly, Control A Assembly, Switch Assembly. In addition, all solder joints are refreshed. Capstan engine disassembled and cleaned, collector polished. Speed switch cleaned. Pitch control poti measured. Everything seems to be ok.

Then I build a bridge over the pins at the speed switch in position 19. The Problem is still there.The switch does not cause the problem.

Next step....
Control B Assembly...

I'm still searching the speed problem

Thanks for any help

Rolf
 
Hi,

Today I found some time to work on the machine. And now the RT 909 works fine

The pinch rollers were set incorrectly. Too much pressure on the capstan shaft. I had done that before. But apparently wrong.

I can only give you one hint: If you restore this machine, then follow exactly the instructions of Rich. In the right order. This saves a lot of time.

Happy new year

Rolf
 
Hi,
have two more problems with my rt 909.

1. When the tape is rewound, the motors stop at the end of the tape, but the brakes are not activated.
2. When i switched from FastForward directly to playback, the machine will not wait until the tape stops. Playback starts too soon. The tape gets involved.

Is it possible that both errors have the same cause? For example, the motion sensor on the left motor?

About Help I would be happy
Rolf
 
RE-RT909 said:
Hi,
have two more problems with my rt 909.

1. When the tape is rewound, the motors stop at the end of the tape, but the brakes are not activated.
2. When i switched from FastForward directly to playback, the machine will not wait until the tape stops. Playback starts too soon. The tape gets involved.

Is it possible that both errors have the same cause? For example, the motion sensor on the left motor?

About Help I would be happy
Rolf
Click to expand...
Sorry. These are not common issues with this model. You will need to troubleshoot and repair now. The service manual has some pretty good theory of operation to help. Just know that some of these kinds of functions are handled by a logic IC that is no longer available. IF you are able to determine all the right inputs to the chip, the chip might be the problem. Normally, these chips are quite robust, unless they have been subjected to voltages that are too high (regulator issues).

The brakes are supposed to drop immediately upon one or both tension roller switches indicating that no threaded tape is present. If the tape does not run out, the motors will reverse torque and bring the reels to near stop, before dropping the brakes, in fast modes. If no tape is loaded, the machine will not stop the reels from fast mode, in response to the stop button, until the tape motion sensor indicates that the reels are near stopped, unless the tension rollers indicate that the tape has run out (it will immediately drop the brakes then.

I don't know how the tape motion pulses are used to indicate a near stop condition. Possibly, the motion sensor pulses are fed into a retriggerable multivibrator. As long as pulse come in at faster than some rate, the circuit holds the output at a certain state. If the pulses come in slower than the set rate, the circuit times out and lets the output change state. I suppose it could have something to do with the reversing issue. I just don't know and I do not have an RT-909 available to test the ideas. Maybe the service manual can help you. Just hope that the multivibrator is not built into the logic chip.

Good luck,
Rich P
 
Last edited:
Hi Rich,

thank you for this information. Your opinion sounds logical. These functions are controlled by ICs.

I think I have too little experience to find the problem. When the stop button is used, everything works correctly. Since I will not sell the machine, I can live with this restriction. Sometimes Ebay sells the circuit boards individually. Do you know which board could be responsible for this mistake? Maybe someday I will find one.

Thank you again for your help.
Rolf
 
I don't recommend just buying the board or chip. That is known as "shotgun" repair. What you need to do is troubleshoot the problem to its cause, and repair that with knowledge. Shooting until you hit the problem will generally be quite expensive, and you won't know if you really got it or not.

Rich P
 
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