Yamaha K720 (K-720) Cassette Tape Recorder

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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
My tape deck - same model as to find under
Le forum de Vintage Audio Laser • Afficher le sujet - Remise en état d'une platine cassette Yamaha K-720
produce sometimes unwanted stop while "play" mode (resp. change the direction after activiating the auto reverse function).
Fast-forward and fast-rewind are fine.
Take-up reel pulses while in playback are present.
This issue is mostly to observe, if the cassette tape goes a bit too stiff (C90, C120)
A second tape recorder device, which is the same model, shows the same unwanted effect. By the use of C 60 cassette tapes the effect is much less frequently.
Those reel, that winds up, remains through stopping reel motor. The other reel, driven by the active capstan, unwinds for a second longer, and then comes the stop-mode or the reverse mode.
The behaviour is the same as to observe, when the cassette to an end is, i. e. the tape is completely unwound at one side.

The question is, which current flow goes in the reel motor in good working condition (the maximum permissible value before the reel motor driver goes shut down and stop the motor).
If I know this value, it is possible to determine, whether the electronic components or the motor itself is the reason for this unwanted effect.
Thanks for your help in advance.
Maybe it is possible to upload a schematic diagram.
 
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Max Headroom

Max Headroom

Banned
Joined 2013
It sounds like the take-up reel drive is slipping.
IIRC, in play mode, the take-up reels are driven from the capstan via idler wheels.
Clean all rubber drive surfaces with alcohol and cotton bud.
Hint:dummy operate the door close/cassette present sensing fingers/switches so that you can run the mech without tape.
You may have to remove cassette compartment dress inner plate to gain access to the rubber drive surfaces.
You may have to manually rotate the supply reel to prevent auto stopping.

Dan.
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
Thanks for this replies.
Max Headroom said:
It sounds like the take-up reel drive is slipping.
IIRC, in play mode, the take-up reels are driven from the capstan via idler wheels.
Clean all rubber drive surfaces with alcohol and cotton bud.
Hint:dummy operate the door close/cassette present sensing fingers/switches so that you can run the mech without tape.
You may have to remove cassette compartment dress inner plate to gain access to the rubber drive surfaces.
You may have to manually rotate the supply reel to prevent auto stopping.

Dan.
Click to expand...
This I have done. The take-up reels are not driven from the capstan. There is an extra motor for the reels in use. The take-up reel of this motor (without rubber drive surfaces) goes from right to left, dependend of the selected direction. Take-up reel and the reel motor itself stops at the same time.
Either the motor is faulty or the appropriated motor drive and motor control unit.
Therefore the question is, whether the motor itself is defectice (motor control unit goes in the protection mode) or the motor control unit itself.
Tho determine this, I want to know the motor current value of the reel motor.
 
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Mooly

Mooly

Administrator
Joined 2007
Paid Member
Reel motors (generally) can be troublesome. As a quick test why not disconnect it (mechanically and electrically) and give it a fast spin on 6 or 9 volts each way around to see if it helps clean it up.

Any rubber parts in contact with the reel motor pulley can shed small particles that migrate down the shaft and cause the bearing to seize. A good reel motor (typically) should just about turn on its own even using a DVM's diode range (or an AVO8 on X1).
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
nothing of this proposals was helpful. A friend of me uses from this model 3 devices, all with the same unwanted effect as described in post #1 (fast-forward and fast-rewind are fine, but stops immediately in "Playback"-mode for both directions - no impurities and poisoning on the tape wheels and idlers).

In the meantime service manual is online - go to
http://diagramasde.com/diagramas/otros2/Yamaha K-720.pdf
The reason seems to be, that the MCU is not getting take-up reel pulses while in playback. On the reel base assembly I note a magnet ring and on the sensor circuit board there is to find a hall generator IC in a transistor outline like TLE4905L - go to
https://www.reichelt.de/?ARTICLE=25...26782519998&gclid=COW2w7iC_s8CFTMo0wodSm0Now:
(genuine part No: G838/G.38, Yamaha part-No "IG 03 04 50")
Which of the parts undergoes an aging ? Actually nothing of both parts are mechanical parts like microswitches.
Thank you for advices.
 
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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
tvi said:
Took me a while to join all the pages
hope it helps regards james
Click to expand...
Thank you very much for the schematic.

tiefbassuebertr said:
Thanks for this replies.

This I have done. The take-up reels are not driven from the capstan. There is an extra motor for the reels in use. The take-up reel of this motor (without rubber drive surfaces) goes from right to left, dependend of the selected direction. Take-up reel and the reel motor itself stops at the same time.
Either the motor is faulty or the appropriated motor drive and motor control unit.
Therefore the question is, whether the motor itself is defectice (motor control unit goes in the protection mode) or the motor control unit itself.
Tho determine this, I want to know the motor current value of the reel motor.
Click to expand...
My estimate was right. Reel motor works fine at all voltages (external check at a regulated power supply) so as in the fast-forward and fast-rewind mode.
Also take-up reel pulses while in playback are present as already mentioned in post #1.

Thus the motor control unit with used BA6209 (reversible motor driver IC) is the reason. Maybe C201 (1/50 bp) and D122 (3V6 zenerdiode) could be the reasons for the unwanted behaviour. I will report again, when this cassette deck is transferred in the correct working condition.
 
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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
tiefbassuebertr said:
Thank you very much for the schematic.


My estimate was right. Reel motor works fine at all voltages (external check at a regulated power supply) so as in the fast-forward and fast-rewind mode.
Also take-up reel pulses while in playback are present as already mentioned in post #1.

Thus the motor control unit with used BA6209 (reversible motor driver IC) is the reason. Maybe C201 (1/50 bp) and D122 (3V6 zenerdiode) could be the reasons for the unwanted behaviour. I will report again, when this cassette deck is transferred in the correct working condition.
Click to expand...
Now I fix the issue. D122, which operates in parallel mode with D120 only while "PLAY", was the reason for the unwanted stop command - the value of motor voltage in both directions was only 2400mV instead usual approximately 3200 until 3600 mV at two devices of this model. At a third device of this model the motor itself is faulty, because an unwanted stop-mode occurs only sporadic and very rare. All devices of this model now operates fine in all respects.
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
tiefbassuebertr said:
Now I fix the issue. D122, which operates in parallel mode with D120 only while "PLAY", was the reason for the unwanted stop command - the value of motor voltage in both directions was only 2400mV instead usual approximately 3200 until 3600 mV at two devices of this model. At a third device of this model the motor itself is faulty, because an unwanted stop-mode occurs only sporadic and very rare. All devices of this model now operates fine in all respects.
Click to expand...
For replacement I need this motor:
Sankyo BFS9B03 (also used in the casette deck D-550M from Sansui) - go to
Sankyo BFS9B03 With Original Pulley Rotating Gear Assembly
Unfortunately only available in the United States.
Who know a delivery source resp. ordering address in Europe from a such a motor with other type/model number but the same specifications?
Thank you for your advices.
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
tiefbassuebertr said:
Reel Motor Mabuchi RF-500TB-12560 as Sankyo BFS9B03 replace

This seems to be the right way:
Reel motor replacement for Sankyo transport.. - Tapeheads Tape, Audio and Music Forums
Datasheet
http://www.electronicaestudio.com/docs/SHT-034.pdf
This reel motor is also in use in Kenwood's KX1100HX - check the images under
http://old-fidelity.de/thread-3232.html
This motor I will order in the next time.
Click to expand...
all URL's dead
http_www.tapeheads.net/showthread.php?t=52148:
only members get in the meantime access authorization
Datasheet:
https://web.archive.org/web/20170702190900/http://www.electronicaestudio.com/docs/SHT-034.pdf
This reel motor is also in use in Kenwood's KX1100HX - check the images under
https://old-fidelity-forum.de/thread-3232.html
https://web.archive.org/web/20170828100555/http://old-fidelity.de/thread-3232.html
 
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