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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 24th Mar 2020, 3:47 pm   #1
DeepHouseman
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Default Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Hi. In order to repair my Sony WM-D6C I have found that during normal playback the player acts as well.
Otherwise during recording either from mic or line-in the tape gets recorded with a high-frequency sound of the motor spinning superimposed (maybe it is the sound of the brushes inside the motor).
This can be clearly heard during the following playback.
The sound can be heard also using batteries.
Any hints?
Best regards and thanks

Steve
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Old 24th Mar 2020, 9:32 pm   #2
Goldieoldie
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

I would check the routing of the two wires connecting the motor to the circuit board .
Especially if it has been repaired.If they are near the preamp it could cause the fault.
If you take the bottom off the unit you can see these wires .
Also check the earthing of the circuit board to the main frame .This is archived with screws holding the board .
Be very careful with the wires connected to the board,they have a habit of falling off !
Try playing back a known good tape and move the wires to see if it cures the problem
Cheers,
Pete
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Old 25th Mar 2020, 7:54 am   #3
TIMTAPE
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Also, generally, a motor which is labouring under excessive load (although perhaps still maintaining correct speed) can transmit increased interference through modulation of the power supply rail and even interference through sparking at the brushes and commutator.

Good service manuals sometimes quote an acceptable motor current draw figure in normal conditions.
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Old 25th Mar 2020, 7:48 pm   #4
Goldieoldie
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Good point about motor loading.
There is a nylon bearing at the bottom of the capstan which is adjustable with a screwdriver
Check to see if it's too tight !
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Old 26th Mar 2020, 9:09 am   #5
saxmaniac
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

The manual is readily available, I've got pdf if you need it. Is the motor running at the correct speed and steady?
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Old 26th Mar 2020, 10:41 am   #6
DeepHouseman
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Hi. Thank You all for your quick reply. I really appreciate it. Apparently the motor does not have any issue, it is running at correct speed and stable. I have not yet measured current consumption. The strange fact is that this behavior appears only during recording on tape. With empty slot or even a blank cassette playback and also during cueing through headphones the recording the problems does not occur.
So it has to be in the recording chain. Maybe the erase head is injecting on tape the noise?
I have a 49 pages long service manual. Does not know if it exist a detailed one.
Thank you all again
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Old 26th Mar 2020, 11:27 am   #7
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Hi Steve, the Sony WM-D6C uses a servo chip to drive the motor but if speed is OK its probablly working. To prove it try slowing the motor slightly by hand to see if the interference pitch changes. Sony use an inverter from the batteries to derive about 50v or so for the record circuit. This is housed in a small square can about 20mm sq. If the output filtering is bad this could give noise only on record. Beware that Sony used neg centre pin on the power input and there is no protection diode. One I repaired had an OC resistor inside this can so I know Its easy to open. Superb machines, and I usually hate cassettes !

Peter
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Old 26th Mar 2020, 11:32 am   #8
DeepHouseman
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Here you can find the sound that was recorded without any input. The noise is clearly heard and superimposed on the tape during only recording. I have to check the erase head.
Thank you all
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File Type: zip noise.mp3.zip (334.7 KB, 42 views)
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Old 26th Mar 2020, 3:03 pm   #9
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Quote:
Originally Posted by DeepHouseman View Post
Hi. Thank You all for your quick reply. I really appreciate it. Apparently the motor does not have any issue, it is running at correct speed and stable. I have not yet measured current consumption. The strange fact is that this behavior appears only during recording on tape. With empty slot or even a blank cassette playback and also during cueing through headphones the recording the problems does not occur.
So it has to be in the recording chain. Maybe the erase head is injecting on tape the noise?
I have a 49 pages long service manual. Does not know if it exist a detailed one.
Thank you all again
On hifiengine.com, as well as the standard 49 page Service manual, there are 2 supplements to the manual, one is 3 pages (looks like it just covers a change of Dolby chip) and the other is 4 pages and covers a change to the main board.

Unlikely to be of any help to your issue.

Update - I now see that these 2 supplements are actually incorporated into the 49 page manual, in addition to a couple of other supplements.

Last edited by DMcMahon; 26th Mar 2020 at 3:19 pm. Reason: Update
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Old 26th Mar 2020, 4:05 pm   #10
peterpiper
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Hi Steve, that sounds very like motor noise but does it record audio from, for example a line input. What does that audio sound like?
Peter
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Old 27th Mar 2020, 6:33 pm   #11
DeepHouseman
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Hey! Culprit found!
It was a ground wire that was not properly soldered, but only few copper whiskers!!
It was under a tape so apparently unseen at first sight!!!
Problem solved!!!
After desoldering it, the noise disappeared.
Thank You all, forum
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Old 27th Mar 2020, 9:19 pm   #12
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Well done .
These are notorious for the thin wires falling off !
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Old 27th Mar 2020, 10:42 pm   #13
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Quote:
Originally Posted by peterpiper View Post
Sony use an inverter from the batteries to derive about 50v or so for the record circuit. This is housed in a small square can about 20mm sq. If the output filtering is bad this could give noise only on record.
This is almost true. I had to repair the inverter in my WM-D6C a couple of years ago. The inverter generates 11V from the 6V battery input. The 11V rail runs nearly everything, not just the record circuit. If it's not working then the machine will appear to be dead apart from the 'BATT' indicator. If it's noisy, then everything will be noisy!

I'm glad to hear the OP found the source of the noise problem.

Chris
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Old 28th Mar 2020, 9:04 am   #14
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

The dc to dc converter converts 6v ro 12v for the audio circuits. It's worth doing a few voltage checks just in case something is haywire, maybe isolate stages of the record amp to see where noise is creeping in,assuming it's some sort of pick up? Decoupling capacitors on power rails? 0v track not broken anywhere?



Quote:
Originally Posted by peterpiper View Post
Hi Steve, the Sony WM-D6C uses a servo chip to drive the motor but if speed is OK its probablly working. To prove it try slowing the motor slightly by hand to see if the interference pitch changes. Sony use an inverter from the batteries to derive about 50v or so for the record circuit. This is housed in a small square can about 20mm sq. If the output filtering is bad this could give noise only on record. Beware that Sony used neg centre pin on the power input and there is no protection diode. One I repaired had an OC resistor inside this can so I know Its easy to open. Superb machines, and I usually hate cassettes !

Peter
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Old 28th Mar 2020, 9:07 am   #15
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Default Re: Sony WM-D6C Hi-freq sound of motor heard recorded on tape

Sorry I hadn't read the entire thread when I wrote the above! Well found and you have a superb machine there!
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