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.
 

moamps

diyAudio Member
2002-10-11 8:15 am
Croatia
www.moxtone.com
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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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.
 
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 .
 
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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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.
 
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 .
 
PROBLEM SOLVED:D

I had previously fitted an autotransformer to run this 120V player from 240V. The transformer was fitted at the rear of the player, opposite the standard Tx. Amazingly (to me) the field was somehow influencing the sled motor - but only on TOC search :confused:
Reorienting the new tx has completely solved the problem.
Thanks very much to all, especially Milan, for your input, and apologies for taking your time with a problem of my own making :ashamed:
Cheers,
Dave.