DVD Player: "No disc" message when disc is on tray

Shin · Guest

Hi, I hope someone can help me with this.
I got a Coby DVD-223 some days ago, which wouldn't read DVDR. After looking up for information, I found out adjusting the potentiometer to get a lower value and thus increasing the laser intensity might solve this. So I decided to do it.
I opened the case, took out the drive carefully enough so as not to damage any strap links, and spotted the 2 potentiometers (they are so small). Using a multimeter, I got a reading from both, one being near 580 Ohm while the other was at 1700 Ohm (I think this one is the DVD laser one). I turned the latter with a screwdriver counterclockwise a little, so the resistance value fell to 1560 aprox. I re-assembled the device and tested it, but there was no effect. It still wouldn't read DVDR.
I then opened it again. When I tried to get a new reading from the altered resistor, I couldn't. I got a weird value (6 Ohm?) from it. The other one was showing just like before. Assuming I was somehow meassuring incorrectly, I turned the pot a little more (not much though).
Having re-assembled it again, I got a "No disc" message even though I had placed one on the tray. I also tried with a CD, but got the same result. The scary part is: I can't seem to see the laser beam.
Does someone know how to fix this, or has any idea of why this happened?

Guest · Posted: Thu Nov 10, 2005 2:24 am Post subject:

Based on your description & reading a low resistance all of a sudden---it all points to a non-recoverable shorted laser diode---Classic result of messing around with such critical adjustments that should not be messed with.

Despite what you may read on the net, messing with the adjustments are very risky.........more than likely the laser output was already on the border line & by rocking the pots, you've managed to short it out for good.

Embarassed

FYI: Most if not all players(especially cheapies) are already set to run at peak levels & trying to squeeze more is often a sure bet to laser diode's destruction.

Guest · Posted: Thu Nov 10, 2005 10:26 am Post subject:

After 46 years servicing electronics, there is one thing that never fails to amaze me. A customer will bring in a piece of equipment that they "adjusted" something on and now it doesn't work at all. When asked why they "tinkered" with anything they don't understand, they would say that they felt like something just got out of "adjustment" and there couldn't be a failure with it. If we could just "readjust" the unit back where it should be, that it would be alright. In the first place, 100% of the time, it does have a "failure" to be repaired. Second, unless a neighbor, friend or some unknown "spook" got in the unit ahead of them, an "adjustment control" doesn't move to need readjusrtment. If a readjustment tends to improve their problem temporarily, that is another sign that a component has changed and is headed toward complete failure. Performing a change in a control during this failure, makes it just that much harder to repair "down the road" as now the tech is fighting two problems. The defective component and the alignment change.

Shin · Guest

Thank you for the information.
I actually got this for free from a friend who bought a new one, so that's mostly the reason I decided to do this. I'd lie though if I said I don't regret what happened.
But anyway, thanks again for your reply. At least now I know what went wrong.

crhudman · Guest