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CD player repairs

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 24 July, 2008 » CD player repairs « Previous Next »

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echase
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Username: echase

Post Number: 126
Registered: 07-2007

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Posted on Tuesday, 15 July, 2008 - 12:20 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The most common fault with a CD or DVD player is an increasing failure to recognise discs, culminating in no discs being read.

On the sliding laser head there is usually a variable resistor. I have found that tweaking this a little often cures the problem, although cleaning the lens with isopropyl alcohol also helps a little.

I used to assume that this resistor altered the power level of the laser and that increasing it compensated for the gradual loss of light output with aging, but now think that maybe it is a focus or alignment adjustment. Anyone know what it is for? Some laser heads have 2 or 3 variable resistors. What are the other ones for?
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stylers
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Post Number: 129
Registered: 04-2005

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Posted on Tuesday, 15 July, 2008 - 01:23 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Its for the laser power. tweaking it will usually get it working a while longer, as the laser diode is failing. heads with two trimpots are usually CD/DVD lasers, one for the infrared CD laser and the other one for the DVD laser.
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echase
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Post Number: 127
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Posted on Tuesday, 15 July, 2008 - 01:51 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Increasing the power will help to compensate for a dimming laser. But if increased a lot you would have thought it would still work, albeit at much reduced reliability. In practice though I find there is a small adjustment range over which it will work and going to the too much ‘power’ setting stops it working. Why is this? This is why I thought it might be focus as that has a midpoint value where it is in focus and going either way sends it out of focus.

I have had some lasers go on for years after an adjustment so the laser is not necessarily close to failure when the first adjustment is needed. But others have needed another adjustment soon afterwards so are close to failure. All LEDs and lasers suffer from reducing output with age.
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gordon
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Post Number: 447
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Posted on Tuesday, 15 July, 2008 - 10:14 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The other variable resistors might be to adjust the servos that control the focus/position of the laser. The technology/engineering involved is pretty amazing, when you consider how cheap DVD/CD players are these days.

This site might be of interest,

http://www.repairfaq.org/sam/cdfaq.htm
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steerpike
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Post Number: 381
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Posted on Wednesday, 16 July, 2008 - 12:11 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

At least one Sony I have opened up had 3 trimmers on the optic/laser board: one was laser power, the other were focus gain and tracking gain.

With DVD-combo players I think usually one trimmer for DVD, and one for CD, as Stylers said.

Too much laser power might swamp the RF AGC circuit, resulting in the inability to decode data.

The refusal to play CERTAIN discs I have traced to flakey electrolytics on the power supply board in an Akai player - It seems the switched mode power supply gets noisy when the capacitors dry out, which makes the off-disc RF signal noisy, but that is only problematic if the disc has low reflectivity. Weird. Or maybe logical!
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echase
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Post Number: 128
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Posted on Wednesday, 16 July, 2008 - 11:43 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Gordon that's a very good article. Basically he says don’t touch the power control except as a last resort. The focus and tracking adjustments are the first choice. Trouble is that without a manual it is less easy to identify them than the power control.

I could not follow the logic as at once point it said lasers hardly every fail and next it says that some have very poor life. Maybe its because there is more than one author.
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terrym
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Post Number: 620
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Posted on Thursday, 17 July, 2008 - 11:13 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Being in the repair game (again - !$##@), the percentage of laser failures to other problems is very low, maybe about 5%.

TM
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echase
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Post Number: 129
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Posted on Thursday, 17 July, 2008 - 12:02 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Steerpike how do you find out what controls does what, other than finding the manual for the model?

My repair philosophy for failure to recognise CDs has been in order:

1)Clean lens
2)Tweak control (said by others here to be the laser power)
3)If above fails buy new laser head which usually comes with the whole CD turning mechanism and sled motor too for a quite reasonable £12-£20. E.g. the common KSS210 series ones.

50% need the new head.

I have found that the last always cures it, but it could be argued that if it’s just focus/servo out of adjustment and these controls are not on the head then, whilst replacing the head may get it just back in spec to work OK for a while, it is not really the best cure as it does not get to the heart of the problem.

Terry are you saying that actually only 5% need the new head and that many of the remaining ones could be cured with focus/servo adjustments? But without the manual it’s going to be difficult to do these adjustments so it might be better to pay for a new head rather than a manual.
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steerpike
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Post Number: 384
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Posted on Thursday, 17 July, 2008 - 01:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I'm not in the repair trade - but friends etc. usually arrive at my door with flakey equipment.
Many times it's when the device has come back from the manufacturer, with a "can't repair" quote, either parts not available, or too costly.
NEVER yet have I been unable to locate a necessary part (or substitute) by phoning around; or there are no faulty parts and it just needs cleaning or alignment.

As I said, one Sony is the only one that confused me. I *always* put a dab of paint on the trimmers, so I can put them back to how they used to be if I change them unecessarily. Most models I've opened where the trimmers are on the main PCB have a silk screen marking to show what the trimmer does.

I can generally hear what each trimmer does, by changing it - I don't mean the sound of the audio playback, I mean the chugging noises of the focus and tracking motors. You can also hear from the motor noises when they are correctly aligned, without even 'scoping the servo signals.
Laser power you CAN't adjust that way, but 'scoping the RF eye patrern shows a lot of information, especially if you compare the eye pattern on different quality discs.
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stylers
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Post Number: 131
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Posted on Thursday, 17 July, 2008 - 01:39 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

most modern/highly integrated/cheap CD players/chipsets don't have presets for the tracking/focus at all. They use auto tracking/focus and any issues with these are usually down to the laser or mechanical problems such as dust or sticky sleds/gears. sometimes people are heavy handed and they actually manage to push the hub down on the shaft of the spindle motor, and then the mechanism goes out of its focus adjustment range. Dirty optics are common, and if somebody tells you they've already tried a cleaning disc, clean the lens with a cotton bud and IPA anyway, because those lens cleaner discs are useless, usually they do more harm than good.
As echase said, those cheapo sony KSS series lasers fail all the time, but they are so cheap to replace, it's usually worth the effort. As steerpike said, if you hear a laser making scraping or hissing noises, its usually an indication that the servo's are having a hard time, which can be another indication of poor adjustment or laser failure..
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echase
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Post Number: 130
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Posted on Thursday, 17 July, 2008 - 05:02 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I'm like you steerpike. My friends and family pile me with loads of broken stuff to fix. Or occasionally I acquire it off the local dump or eBay, fix it and sell it on.

Tens of hours work to fix a huge TV that my son acquired fully working off the dump and then broke it by crashing his car with it in the boot may be fun, but not economic!
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741
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Post Number: 89
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Posted on Thursday, 17 July, 2008 - 11:04 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Echase, do you have any useful addresses for Sony laser heads please ?

I have an old Sony CD Player - huge box, mostly empty with an ordinary-looking CD drive inside and small PSU. This seems to mainly show "No Disk".
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echase
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Post Number: 131
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Posted on Thursday, 17 July, 2008 - 11:49 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Shops in Sim Lim Tower in Singapore are best, but since moving back to UK I have found lots of people sell them; try Grandata. TV magazine advertises lots. Many sell generic copies of the Sony one. No idea if they are any good.

Beware that some come with a solder bridge across 2 pads to protect the laser from static (possibly). Remove the bridge before use. Also note that the A, B etc suffix on p/n, if used, matters.

I’d expect a new head unit to cure your problem but others have more experience with diagnosis than I.
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terrym
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Post Number: 621
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Posted on Friday, 18 July, 2008 - 11:14 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Most of the time, the problems are either dirt in the optics or on the mechanics, sticking mechanics, or flaky caps in the power supply (or some bright spark has had a go themselves and knocked the lens off the laser).

It doesn't take much noise on the power supply line to upset a laser and servo system, especially in the cheap rubbish coming out these days.

I probably see 40 - 50 cd/dvd units a month. At worst, have only replaced 5/6 lasers in a month, normally only 1 a month.

TM

Should have added - spindle motors are a more common fault

(Message edited by terrym on 18 July, 2008)
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741
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Post Number: 90
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Posted on Friday, 18 July, 2008 - 09:46 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The CD player works every time if I hand-start it !

That is, at disk-insert time, the spindle 'judders' for a while (always trying to spin in the same direction), then the CD player gives up ("No disk")

If I spin the CD by hand at the same time as the CD player is turned on, the seek works, and the CD player seems normal.
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canonman
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Posted on Saturday, 19 July, 2008 - 03:03 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

See if you can put a *tiny* drop of oil into the top bearing of the spindle motor - it may help!

The easiest way is to put some light machine oil (3-in-1) onto the tip of a precision flat-blade screwdriver, then 'drop' it into the top of the motor where the shaft comes out.
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echase
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Post Number: 133
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Posted on Saturday, 19 July, 2008 - 05:30 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I had got my JVC mini Hi Fi working by altering the ‘power’ control but, having read stuff here, concluded that maybe some other adjustment may be better, so I reinstated the 'power' control on the laser back to where it was. Then I tried the nameless control on the CD processing board. This might have made a slight change as it does now eventually start playing after a lot of sled motor hunting (say 15 secs at the start). But does not work on my know bad test disc

It quickly reads the directory as the tracks are listed on the display, but it always done this. Does this mean that focus is OK?

The labelled 12V supply to the CD board is in fact 13V with 300mV of ripple so maybe the caps are bad. But smoothing this out made no improvement in start time. Have yet to find the 5V supply (assuming there is one) to check this.

Any ideas of what else to try?
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ant
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Post Number: 322
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Posted on Sunday, 20 July, 2008 - 11:58 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello all,

I've often found that the smallest hypodermic syringes and needles are good for getting oil into impossible places!

Regards Ant
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echase
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Post Number: 134
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Posted on Monday, 21 July, 2008 - 11:24 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

741, after an attempt to cure any dirt/lubrication problem and in absence of a better idea from any others with more experience I’d try a new head unit. £15 is not that much to pay.

My cogs, etc. are as clean as the day they were new so don’t think that is my problem. Turning the 'power' control back up again causes my bad test disc to be recognised (just).

If you want somewhere close to what Maplin was before it went to the dogs I’d recommend Sim Lim Tower to anyone on this forum who happens to pass through Singapore. It’s about 50 small shops that sell electronic components / kits etc; new and surplus/second hand. VAT was only 3% (may be 5% now) so prices are good.

Not to be confused with the nearby Sim Lim Square which is 100 similar small shops, rather more computer/ hi fi / camera orientated, but good too.

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