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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 3rd May 2012, 6:40 pm   #1
smirnisio
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Default Uher 4000 report L problems!

Hi ,
I recently bought a Uher RTR.
When checking its working condition I found that the capstan belt goes off and I replaced it with common rubber!

The main problem is this. When I use a tape in the playback position and turn the volume on it hums loud. The tape plays as a background. When turning the volume switch louder or lower I found that the speed changes as well. In particular, when fully turned on and the hum is loud the motor seems to slow down. In middle positions (of the volume control) the speed goes faster.
Does anyone have an idea?

I have already checked if this is a problem from the power source. It is not, both batteries or the transformer give the same result. I also have changed the two 2000uF capacitors with 2200 uF ones and the 1000uF that are beneath the batteries box.

Should I have checked all the capacitors of the amplifier or this is a common problem with a transistor?
Thank you in advance.
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Old 3rd May 2012, 10:02 pm   #2
mrmagnetophon
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Default Re: Uher 4000 report L problems!!!

Hello,

The Uher machines do run slower with the volume turned up, I have always experienced this.
Also I posted on here, that I had problems with mine when I replaced the capacitors with bigger ones, the machine actually ran slower, so I don't recommend anything but what was originally in there.
On the side of the battery compartment, a 1000uF on top and a 2000uF on bottom.
And underneath, the 1000uF.

Also note if you run the light for the meter it slows the recorder down too.
-Chris
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Old 3rd May 2012, 11:04 pm   #3
ricard
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Default Re: Uher 4000 report L problems!!!

Don't these machines have three-phase motors with transistor control, which should offer precise speed control unless something is wrong?
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Old 4th May 2012, 1:35 am   #4
TIMTAPE
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Default Re: Uher 4000 report L problems!!!

I think they are brushless electronically commutated motors but certainly electronically governed.

I don't think they should slow down with high volume or with the light on, unless the batteries are low or there is a power supply problem.

The hum plus the slow speed suggests possibly a diode in the power supply is dead, but if it still does it with batteries, possibly the motor is labouring and the motor load is modulating back into the power rail. Does the "hum" change pitch depending on the motor load?

Does the motor pulley turn freely with your fingers? Is the belt the correct size, ie; not too tight?

Tim
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Old 4th May 2012, 5:44 am   #5
julie_m
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Default Re: Uher 4000 report L problems!!!

They are "not-quite-brushless" motors. Driven like a 3-phase brushless motor, but using brushes (not carrying the full winding current) for position sensing instead of Hall effect devices. Check all transistors on the motor PCB; one going faulty can lead to reduced motor power output.
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Old 4th May 2012, 11:41 pm   #6
TIMTAPE
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Default Re: Uher 4000 report L problems!

ajs,

Thanks for the clarification. Do you know if the Akai X-4/X-5 motors were of the same sort of design?

Cheers Tim
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Old 5th May 2012, 5:37 am   #7
julie_m
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Default Re: Uher 4000 report L problems!

Afraid not, never had one of those Akais. Best bet would be to search for a schematic.
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Old 6th May 2012, 10:54 pm   #8
smirnisio
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Default Re: Uher 4000 report L problems!

hello again,I just follow your advices about testing the motor transistors and i believe that 1 or 2 have problems.
The type of the transistor is the Ac151 r VI.
Should i go for the same one or a Ac151/1 is equivalent and can be used?
thank you!
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