Recently, I had two instances of equipment coming back after some year – with different defects that at their first visit in my workshop. One device is the Meridian 506, a high-class CD player that is popular with hifi enthusiasts, and has been marketed for many years in various different versions. Earlier I had fixed some design issues with the motor driver of the CD deck, see Meridian 506 CD Player: a hot driver.
This time, it wouldn’t detect any CDs, and made some noises. The deck was still opening fine. After looking around, there is no obvious defect, the power supplies are good. All the service modes work – just that I can’t get it read discs or even lock on tracks, it just spins up, then stops.
Reading through all various posts, it seems clearly related to the CD head assembly, this version of the 506 uses a CDM 4/19 Philips laser head assembly, and these are known to wear out over time, i.e., the laser will show aging, and then the mechanism can’t lock on the CD.
Well, easy enough, I found a CD 480 player cheaply as used goods, and this has the desired CDM 4/19.
It arrived strangely packed, but well, better strangely packed than insufficiently packed. Indeed, a lot of styrofoam, chips and paper inside.
Inside, a very simple assembly, much lighter than the Meridian deck. Just some thin plastic.
Easily disassembled the donor.
There are some changes necessary – the hub is different, but can be removed with simple tools (plastic tools) and switched.
Well, all this done, unfortunately —– no success. Still same symptoms. Next, poking around the main TDA chip, there are no signals that are of any use. Strange. Normally it should at least start reading and locking, but it doesn’t (not that the CD drive uses a feedback loop to keep the head on the track, by adjusting the laser arm coil current according the the laser feedback; in these drives, the laser arm is driven by a coil).
After some further study, finally realized that the CD is spinning the wrong way. How can that be? Seems like a defective motor driver! On the small board of the CD deck, there are two L272, and one of them is terribly hot. Not good.
The L272 has long been obsolete, but I would two pieces cheaply on a Chinese website, these were apparently no new but recovered from used equipment. Well, no problem, I rather buy used parts than fake parts.
With these repairs done (not easy because the soldering of the L272 is very strong, need to put a lot of heat to the small board because all the ground pins are firmly connected to a ground plane), the Meridian is working great again, let it play for several hours with no skipping.
And, we now still have a spare laser head assembly should it fail next.