Supratech DVD, odd tracking problem

[Jeroni Paul]

I'm looking at a DVD player with an odd problem in the tracking actuator servo. When a DVD is loaded, both original or recorded, it focuses, spins and positions the lens fine - up to this point the tracking actuator keeps the lens centered. Then suddently the lens moves to one end of the tracking actuator range, a click is heard as the actuator hits a plastic stop and the sled does not move. This situation lasts about two seconds until it retries by moving back and forth the sled, refocusing and reactivating the tracking servo - the same repeats. After two tries a disk spin down and spin up happens and the read is attempted two times more before a disk error message pops up.

This tracking failure happens almost always, but occasionally it will load and play the disk for a while but sooner or later the lens clicks again. I've seen it click, then recover and continue to play. It does not respond to mechanical stress to the board. I suspect this failure happens more often at higher spindle speeds, that may explain why original DVD are harder to get to load than DVD-R. I have double-ckecked the motor for shorts in windings or rotary contacts problems and could not find anything strange.

With CDs the behaviour is different, the tracking actuator does not click to one end but it has some difficulties keeping the tracking stable and the data readout error free, with occasional sled repositionings as if it had some trouble reading the data. These sympthoms happen more at the beginning and mid way tracks and never at the outmost tracks. I relate that again to the lower spindle speed in these tracks.

The player is a Supratech vision Artemis (DVD player with USB, card reader and DVB-T tuner) and has board SUNPLUS 8202A with SPHE8281A chip (256 pin version) and a Sanyo HD850 pickup. The SPHE8281A outputs the tracking actuator signal on pin 42 labeled DATEO and that is input to the CD5888CB (actuator and motor driver) through a 68K resistor. Monitoring this signal reveals a voltage of 1.5 to 1.7V during normal operation and jumps to 2.5 to 3.0V when the click occurs. There are three more pins on the SPHE8281A related to tracking, the names are referenced in the datasheet but no more details are provided:
pin 34: TEO (Tracking error signal output)
pin 35: TEOLP (TEO low pass?)
pin 26: V165 (Reference DC BIAS voltage)

The datasheet refers to a servo datasheet for additional information that I could not find. Signals TEO and TEOLP follow the same behaviour as DATEO, and V165 is always 1.6V. TEO has a 330p capacitor to ground and TEOLP a 100nF one. I've checked all servo supplies and grounds and ruled out the power supply by powering it with a PC power supply. The board runs off a single 5V supply and has its own 3.3 and 1.8V regulators. I've checked all capacitors for ESR.

Thank you in advance for your replies.

 

Check for some mechanical issue re the holding of the disc. If it
is loose and can wobble or if it can slip in rotation, that makes
it more difficult for the tracking.

 

[N_Cook]

On 14/11/2015 23:44, makolber@yahoo.com wrote:

Check for some mechanical issue re the holding of the disc. If it
is loose and can wobble or if it can slip in rotation, that makes
it more difficult for the tracking.

And similarly. If a problem in the suspension , just at the usual
neutral posistion. Try a piece of gummed paper or similar stuck to the
platter, to shift the positioning a bit. If that is worse then,
perhaps the platter has moved on the spindle. Usually just relies on
friction fit so faced with a hard to remove disc and the platter gets
out of position. Can you check the platter height against another with
the same optical deck?

 

[Mark Zacharias]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:n29mbc$goa$1@dont-email.me...

On 14/11/2015 23:44, makolber@yahoo.com wrote:
Check for some mechanical issue re the holding of the disc. If it
is loose and can wobble or if it can slip in rotation, that makes
it more difficult for the tracking.


And similarly. If a problem in the suspension , just at the usual neutral
posistion. Try a piece of gummed paper or similar stuck to the platter, to
shift the positioning a bit. If that is worse then,
perhaps the platter has moved on the spindle. Usually just relies on
friction fit so faced with a hard to remove disc and the platter gets out
of position. Can you check the platter height against another with the
same optical deck?

It is not uncommon for there to be an increasing distance between the
objective lens and the disc as the sled moves further along it's track. This
means an increasing focus error. If the laser is aged, the servo can no
longer account for this as reliably.

(I assume you have cleaned the lens.)

In any case - these things are usually repaired by replacing the entire
traverse unit, if they are repaired at all.

Most players are so cheap anymore, they simply aren't worth it.


Mark Z.

 

[Jeroni Paul]

Mark Zacharias wrote:

"N_Cook" wrote in message
news:n29mbc$goa$1@dont-email.me...
On 14/11/2015 23:44, wrote:
Check for some mechanical issue re the holding of the disc. If it
is loose and can wobble or if it can slip in rotation, that makes
it more difficult for the tracking.


And similarly. If a problem in the suspension , just at the usual neutral
posistion. Try a piece of gummed paper or similar stuck to the platter, to
shift the positioning a bit. If that is worse then,
perhaps the platter has moved on the spindle. Usually just relies on
friction fit so faced with a hard to remove disc and the platter gets out
of position. Can you check the platter height against another with the
same optical deck?




It is not uncommon for there to be an increasing distance between the
objective lens and the disc as the sled moves further along it's track. This
means an increasing focus error. If the laser is aged, the servo can no
longer account for this as reliably.

(I assume you have cleaned the lens.)

In any case - these things are usually repaired by replacing the entire
traverse unit, if they are repaired at all.

Most players are so cheap anymore, they simply aren't worth it.


Mark Z.

Thanks for all the replies. I belive the problem is in the electronics and maybe inside the big IC.
- There is no apparent mechanical problem with the disk clamp.
- I have played with the disk height with no improvement.

There are details that do not fit with an aged laser. That was my first tought too, but I think the laser is fine. First it is able to read really weak disks, I have one I recorded in a defective burner that few players can read - and this one can. Second the unit behaves better at the outer tracks as opposed to what a weak laser would do. And third, the tracking actuator clicking to an end is not the expected behaviour, that seems to me an electronic fault.