Hi,
I am an idiot. I am enjoying my DENON DVD2900, so I thought I would get another one. Being an idiot, a broken DVD2800 turned up, duh. It has the nice HDCD device in though. It didn't recognise disk, so I got a new laser off ebay (being an idiot) and have now fitted it.
To my surprise it works, sort of.
Put in a pristine CD and will load up and play sometimes quickly sometimes less.
Put in a less than pristine CD and sometimes it will load and play happily quickly and sometimes not atall.
Put in a playable but pretty damaged CD, chuggs and spins, doesn't play.
So it seems to be sometimes struggling to read the disk. When it does, it plays fine all the way through and skips between tracks quickly.
Powering up and opening and closing the door seem to be the things that affect the how well it recognises / reads the disk.
The service manual is not very forthcoming,has a few pictures of what happy disk loading ought to look like but no corrective measures, there are no tweaky pots, just mechanical adjustments, and all the test points are under the transport. So I haven't successfully looked at them on the scope yet.
The power rails look ok enough 5v rails vary between 4.5 and 4.9.
I am tempted to try replacing a few strategic PSU caps (I am a professional (idiot) I won't kill myself) just incase and investigate the power rail voltages a bit further.
Any bright Ideas?
thanks
I am an idiot. I am enjoying my DENON DVD2900, so I thought I would get another one. Being an idiot, a broken DVD2800 turned up, duh. It has the nice HDCD device in though. It didn't recognise disk, so I got a new laser off ebay (being an idiot) and have now fitted it.
To my surprise it works, sort of.
Put in a pristine CD and will load up and play sometimes quickly sometimes less.
Put in a less than pristine CD and sometimes it will load and play happily quickly and sometimes not atall.
Put in a playable but pretty damaged CD, chuggs and spins, doesn't play.
So it seems to be sometimes struggling to read the disk. When it does, it plays fine all the way through and skips between tracks quickly.
Powering up and opening and closing the door seem to be the things that affect the how well it recognises / reads the disk.
The service manual is not very forthcoming,has a few pictures of what happy disk loading ought to look like but no corrective measures, there are no tweaky pots, just mechanical adjustments, and all the test points are under the transport. So I haven't successfully looked at them on the scope yet.
The power rails look ok enough 5v rails vary between 4.5 and 4.9.
I am tempted to try replacing a few strategic PSU caps (I am a professional (idiot) I won't kill myself) just incase and investigate the power rail voltages a bit further.
Any bright Ideas?
thanks
You've ignored the fact that your supposed "new" laser might not be 100% (the odds are high in this day and age)
In your position I'd send it back and get a 2nd replacement laser (preferably from a different supplier) and retest
PS:Bad form to tack your new question onto the end of an unrelated thread
hmm continuing on the idiot theme, no idea how that happened, I thought I started a new one. nevermind and thanks for moving it.
No, I won't send it back, it plays just fine, when it has found the disk, it is very interesting, because it is a red DVD laser you can see it through the disk trying to come in and out of focus. I tried and failed to read the laser current, broke off a pad and became discouraged. need to use an even thinner wire... Was interested to note in the service manual the laser needs more mA to read a CD than a DVD, would have thought it was the other way round...
To be honest I cannot tell if it has one or 2 lasers, there seems to be 2 different sets of current measuring resistors for the diode current, but only one RF test point.
I have replaced a couple of capacitors on the power supply board and now the voltages are much more sensible , i.e. the 5 v is 5 volts now. rather annoyingly it now won't play anything.
quite tempted to put the original laser back...
For whatever reason I don't seem to be getting current any current in to the CD laser. I am getting current in to the DVD laser. Going to be fiddly to diagnose that one. The signal from the LDO2 does not go negative, and it should. It drives a pnp transistor which is a current source into the laser diode.
More idiocy on my part. I had forgotten that the current source is referenced to the 5 volt rail, which explains why i thought it should go negative, as when I looked at it my scope ground was on the 5 volt rail, as recommended in the service manual.
I think I have only fixed one CD player so far in my life, and that was after a transport transplant, only to find the supposed faulty transport was fine. I discovered a capacitor had gone high impedance and caused a power rail to oscillate.
So i will call this a partial success in that i bought up the power rails to the right place by replacing a couple of capacitors.
The more time I spend looking in to this box, the more I think this is a good candidate for a transport swap. I.e. I will fit it with a CDROM drive and keep the original DAC board. It uses an AD1854 device. I have no idea how respected that device is, but it is delta sigma type.
I have done a similar CDROM based player in the past, using NOS TDA1543, into a valve current to voltage converter. it sounds very lovely and has remarkable timbral definition in the lower registers, the top sounds fine, but a player with proper oversampling type of filter sounds more natural in comparison, so this is what I intend to pursue with this next project.
it will be documented here:
The eternal CD player - DIY - HiFi WigWam
Thanks for the comments.