TEAC laser TOC search position - help, please! - diyAudio
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Old 8th June 2005, 12:35 PM   #1
dnsey is offline dnsey  United Kingdom
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Default TEAC laser TOC search position - help, please!

My Tascam CD-701 (similar to TEAC VRDS) suddenly stopped reading the TOC on loading discs.
On investigation, the pickup is starting its search too far from the CD periphery (outside the diameter), so it times out before reaching the correct position, although it does advance and search OK. If it's nudged towards the centre, it will find the TOC and proceed as normal.
There's no tightness in the sledge, nor is there a dead spot, as it returns smoothly and correctly on ejecting the disc.
I'm not sure how the sledge is initialised, or what would cause the fault (firmware problem?).
Any help or suggestions would be very welcome.
Thanks.
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Old 8th June 2005, 10:44 PM   #2
moamps is offline moamps  Croatia
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Hi,
Check sled balance first :
1. In Stop close the disc tray with no disc loaded.
2. Adjust VR6 for 0V at between TP-1 (SD.D) and GND.

If the fault still remains, I can scan for you relevant parts from the service manual, which may be useful in fault finding.

Regards,
Milan
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File Type: jpg sd.jpg (27.6 KB, 139 views)
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Old 9th June 2005, 01:37 PM   #3
dnsey is offline dnsey  United Kingdom
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Thanks for that, Milan.
Unfortunately, nullling the sled balance doesn't help - in fact the laser approaches the CD bit closer when VR6 is turned fully clockwise.
I think I have the manual somewhere, but as far as I remember there are no real schematics - just block diagrams.
If you have any other suggestions, please let me know!!
Cheers,
Dave.
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Old 9th June 2005, 02:01 PM   #4
guytou is offline guytou  France
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Hi, maybe i understood wrong what you said , because normally the first step of the start sequence is that the pickup goes to the center of the disc , since the TOC is located on the inner circle .
So when you light on the player , the first thing you have to see is the pickup going to the center .If you don't see , it's probably a tray misalignment ( depend of mechanism , what is it?) . So you would'nt have to push the pick-up until the center .
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Old 9th June 2005, 07:34 PM   #5
dnsey is offline dnsey  United Kingdom
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Hi,
The laser starts to move towards the disc, but only gets as far as shown in the picture. I noticed when taking the photo that if the power is switched off and then on again, it will move a further step of the same distance each time. I think the tray is OK, but the laser initialisation is faulty (too short a time or too few steps).
Do you know how the distance is determined?
Cheers,
Dave.
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File Type: jpg cd.jpg (31.5 KB, 133 views)
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Old 9th June 2005, 08:02 PM   #6
dnsey is offline dnsey  United Kingdom
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To clarify a little:
When a disc is inserted, the sled advances from its rest position about 1cm. As the laser cannot 'see' the disc from there, it shuts down and resets. If the sled is nudged so that it can see the disc before the reset, it advances in 1cm steps until it finds the TOC, and is fine from there on. If the power is turned off and on before the reset, the laser advances 1cm each time.
It appears that the initial 1cm step should be more than 2cm, so that the laser can see the disc and seek the TOC, but I don't know what governs this movement.
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Old 9th June 2005, 08:06 PM   #7
moamps is offline moamps  Croatia
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Hi Dave,

With the player in off position, check with your finger to see if the laser pickup moves very easily in and out.

If not, clean the pickup shaft and oil it gently.

Regards,
Milan
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Old 9th June 2005, 08:48 PM   #8
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Talking cd player

I had exactly the same fault but a totally different model cd player...cleaning and light oiling of the shaft upon which the optical block sits was the cure...the clue was that the block seemed tight on the runner and wasnt entirely free to move,
regards mike
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Old 9th June 2005, 10:33 PM   #9
guytou is offline guytou  France
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Hi dave , I could say anyway the sled motor is feeded until it meets it's end of course contact (near of the center ) .So I'm thinking a sled problem too , maybe fail of oil , but I don't thihk .
I would think rather of sledmotor brushes sooted up .
So you could attempt the following procedure :

1-find the sledmotor connexions
2-disconnect the sledmotor from the CDP.
3-apply a low tension (say,4,5V) back & reverse to the motor .
4-This way , you could see your sled going to the center right & doing a bizarre sound at the end of course (normal , it's the end-of-course clutch).
5-Repeat 4 or 5 times : normally , it's sufficient to clean up the brushes .
6-Now , connect again the sled motor to the CDP and check what's happening .

I've already salved a CDP with this .
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Old 10th June 2005, 12:10 AM   #10
moamps is offline moamps  Croatia
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Quote:
Originally posted by guytou
......
I would think rather of sledmotor brushes sooted up .
.....
Hi,
Sledmotor in CD701 is brushless linear type.

Regards,
Milan
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