Burnt laser in CD optical pick up block - Page 1
Forum section: electronics / repair

author: nuno
author_rank: Frequent Contributor
timestamp: June 14, 2020, 02:48:33 pm
content: I have this 80's or 90's Sony PMC-303L mini sound system for repair on complaints that the CD doesn't work.I traced the issue to the optical pick up block laser being burned (CD not detected; no visible light from the lens and the current way too high). So now what? Can't find info on this block, and no replacement part. What do you guys do in these cases?Thanks

author: TheMG
author_rank: Frequent Contributor
timestamp: June 14, 2020, 03:25:11 pm
content: Browse eBay and try to find a similar unit to pull parts from, and hopefully it has a good pickup in it.You could try to replace the laser diode but the way most of these assemblies are built they are usually glued in and it would be a very delicate and fiddly operation, which may well end up damaging the pickup assembly beyond repair. Then again, you've got nothing to lose at this point.

author: eurgenca
author_rank: Regular Contributor
timestamp: June 14, 2020, 05:50:57 pm
content: Hello.I think your stereo use KSS213B laser unit. Please check or paste picture of laser unit. KSS213B is not hard to buy.Regards.

author: nuno
author_rank: Frequent Contributor
timestamp: June 14, 2020, 07:27:01 pm
content: That's right, it's a KSS-213B/S-N. Damn, I searched for the system's name + "laser block" and didn't remember to search for the block's part number. I have found it now, even locally. Many thanks to you all.

author: nuno
author_rank: Frequent Contributor
timestamp: June 14, 2020, 07:40:48 pm
content: eurgenca, the manual speaks of a calibration procedure when the block is swapped, requiring a special CD... have you ever done that and used the CD or can we live without it? Thanks

author: amyk
author_rank: Super Contributor
timestamp: June 14, 2020, 10:12:51 pm
content: CD players use an IR laser, you will not see visible light (and do not be tempted to look into the beam... with your remaining eye!)

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 14, 2020, 10:35:04 pm
content: You can check whether the laser is working by using the camera on your phone, or indeed a camera.You can easily prove this right now by pointing your phone camera at any remote control you have beside you and pressing a button.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 14, 2020, 10:39:58 pm
content: Quote from: amyk on June 14, 2020, 10:12:51 pmI swear that over a couple of decades, with what remains of my retinae, I've been imagining spots of Red light coming out of CD player lenses, time to get my eyes checked...?

author: Circlotron
author_rank: Super Contributor
timestamp: June 14, 2020, 10:44:30 pm
content: Quote from: Audiorepair on June 14, 2020, 10:35:04 pmYes, but not all phones. iPhones have an IR filter on the main camera lens. The selfie camera works alright for detecting IR though.

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2020, 11:32:42 pm
content: Quote from: shakalnokturn on June 14, 2020, 10:39:58 pmCD players use a near-IR laser, 780nm if memory serves me right. It appears as a dim red light, not completely invisible.

author: nuno
author_rank: Frequent Contributor
timestamp: June 14, 2020, 11:50:29 pm
content: Yes, you can see a faint red light (can also be seen for example in some night lights IR LEDs from security cameras).This is the procedure recommended in the service manual for the system to check for laser light.But anyway, a current limiting resistor for the laser is falling into pieces due to excessive heat and being traversed by 220mA.

author: eurgenca
author_rank: Regular Contributor
timestamp: June 15, 2020, 05:31:33 am
content: Hello.Search for service manual in most of them you have descripted how to calibrate laser replacement. But usually is just replacement o.k.P.S.This will help.:

author: nuno
author_rank: Frequent Contributor
timestamp: June 15, 2020, 11:05:12 am
content: Ok, thanks eurgenca, I have the service manual, I was just concerned about the test CD they speak about. The block is cheap, I'll try anyway.

author: nuno
author_rank: Frequent Contributor
timestamp: June 20, 2020, 10:35:09 am
content: Just to let you all know that I replaced the optical pick up block and it worked right away, no adjustments were necessary. Many thanks

author: YetAnotherTechie
author_rank: Regular Contributor
timestamp: June 22, 2020, 11:12:43 pm
content: Use a good quality aluminium CD, not a recordable, nor a gold one. the older cds are usually better it shoud look really like a mirror from the top. As years went by the manufacturers used less aluminium and they began to look transparent. Adjust tracking near the edge of the disc.Do not touch the power setting pot on the new block!Be sure to remove the transport short-circuit on the block (if it exists), you need to remove a solder bridge with a soldering iron.

author: nuno
author_rank: Frequent Contributor
timestamp: June 23, 2020, 04:12:08 pm
content: The funny thing is that the box of the replacement part has"Remove antistatic lock before use"on 4 sides, but never says what/where is it exactly

author: Buriedcode
author_rank: Super Contributor
timestamp: June 23, 2020, 04:39:45 pm
content: Quote from: nuno on June 23, 2020, 04:12:08 pmOn the units I've used, they were solder bridges that had to be removed. These shorted out the diode to prevent ESD damage.Edit: whoops! just saw this was already mentioned, sorry.

author: james_s
author_rank: Super Contributor
timestamp: June 23, 2020, 05:54:41 pm
content: Well since it works, clearly there is no solder bridge that needs removing from this particular pickup.

author: nuno
author_rank: Frequent Contributor
timestamp: June 23, 2020, 10:38:44 pm
content: There was a solder bridge, I removed it.