Philips CDM 12 IND mechanism not playing CD's - Page 1
Forum section: electronics / repair

author: adinsen
author_rank: Regular Contributor
timestamp: January 01, 2024, 07:41:44 pm
content: MyBeosound Centurysystem cannot play CD's any more. It's a mid-1990's hi-fi semi-portable system with FM/CD/Cassette. The CD player is a Philips CDM 12 IND high-end cd-mechanism. The spindle does not spin and the pickup does not move. I can see that the mechanism attempts to focus when I start the CD.Bang & Olufsen implemented a test mode in the system which allows me to control the spindle and pickup position motors from the UI, as well as starting playback. Activating either motor from the UI has no effect. The error code for "focus errror" is displayed after a while when starting CD playing in test-mode, even when there's a CD in the drive. The CD never spins and the pickup motor doesn't move, however.I can make both motors spin when I apply 2.5V over them, so I am suspecting a problem with the output driver.I cannot find a service manual or schematic for the CD-drive. CDM12 is common, but the "IND"-version (for "industrial") is apparantly mostly used in jukeboxes, and by Bang & Olufsen consumer productsHowever, I've identified two TDA7073 output driver IC's on the board (datasheet:https://www.nxp.com/docs/en/data-sheet/TDA7073A_AT.pdf). I soldered wires on the board to connect my scope and it seems that IC is indeed dead: There's no signal coming out at any timebaseI've checked the 47uF electrolytic decoupling capacitors on the TDA7073's, and they are nominal.I find this a little strange, however, as the TDA7073's are supposed to be very robust driver IC's, and why have both differential outputs apparantly died at the same time - and nothing else? So I'm thinking that I might be missing somethingInput and ideas will be appreciated!I've attached some photos of the board and the mechanism.Thanks!

author: CaptDon
author_rank: Super Contributor
timestamp: January 01, 2024, 07:47:08 pm
content: Look at the input signals to the driver chips. Are they even enabled and expecting to run?

author: adinsen
author_rank: Regular Contributor
timestamp: January 01, 2024, 08:28:27 pm
content: Well that was obvious. No, I can't measure any signal on the input eitherThere's no way of enabling or disabling these drivers, but they're getting 10V as they're supposed to. I've seen the commands work a couple of years ago. I can see the host computer sending something and the drive replying something on the command interface.

author: adinsen
author_rank: Regular Contributor
timestamp: January 01, 2024, 09:22:13 pm
content: Ok, so my measurements were uselessI can now visibly see the pickup move slightly. I.e.: The driver IC is not defectiveAlso with the motors connected, I now see 5V on both sides of the two differential outputs (positive/negative 1/2), which indicate that the servo MPU is just not runinng the motors. Hmm. The B&O service manual describes another CD-drive mechanism so the diagnostic commands are not 100%.The board has these chips:OQ8868. According to this datasheet, this is the chip that controls everythingexcept spindle:https://www.alldatasheet.com/datasheet-pdf/pdf/18014/PHILIPS/OQ8868.htmlSAA7345. This is the audio decoder -this contains the spindle motor controller:https://www.alldatasheet.com/datasheet-pdf/pdf/19054/PHILIPS/SAA7345.htmlSAA1305T. This is described an on/off logic IC:https://www.nxp.com/docs/en/data-sheet/SAA1305T.pdfS87C654: The 8051-derived MCU:https://html.alldatasheet.com/html-pdf/15893/PHILIPS/87C654/495/2/87C654.htmlThe SAA7345 datasheet lists commands to control the spindle - start/stop etc.I'm wondering if the problem I'm seeing could be caused by a defective pickup and something in the SAA7345 which means that it's for some reason rejecting the commands to start the spindle? The real life pattern I've seen is that the player USED to work intermittently but now does not work at all. This could be consistent with a failing pickup.

author: Haenk
author_rank: Super Contributor
timestamp: January 02, 2024, 10:04:16 am
content: The problem is - it's not a case of "power on, CD plays". There are several conditional steps involved, before the CD actually starts to play.Usually it's something like:- laser power on, check for reflection- motor on- move head to start- move head to track and try to read trackWith a bit of luck, this is detailed in the service manual.Common faults are: weak laser, bad driver IC, bad caps of driver circuit

author: Runco990
author_rank: Frequent Contributor
timestamp: January 02, 2024, 04:34:14 pm
content: I've repaired a TON of these on B&O and other systems. In general, the laser is weak. Very common fault. I have also found that DUST settles inside the optics, making the pickup blind. Sometimes you can pull off the laser board and clean the surface as well as the angled mirror inside the assembly and it'll run fine again. Can't hurt. A replacement pickup is around $30 or so from Liberty Electronics.

author: adinsen
author_rank: Regular Contributor
timestamp: January 03, 2024, 09:31:38 pm
content: Thanks very much, both!I was looking at eBay for replacement pickups, e.g.https://www.ebay.com/itm/394740344542but got seriously in doubt whether or not they are the actual pickup or just the lens. Perhaps it's just a bad translation from Chinese, but when yesterday I saw a working Century offered for less than a new known quality pickup, I went and bought it.So now I have two: A black Century that can play CD's - plus my own green one that can'tQuote from: Haenk on January 02, 2024, 10:04:16 amUnfortunately what's in the serivce manual doesn't help as it describes another mechanism than the CDM12IND. Caps are good and drivers too, and the pattern of problems I've seen indicate a weak laser.Quote from: Runco990 on January 02, 2024, 04:34:14 pmThis is interesting and definetely worth trying! I'll work on that and report back. If it doesn't help, then this one looks genuine:https://www.ebay.de/itm/154637570693Thanks again