An Obiturary: LiteOn SOHW-1633S, and LH-18A1P

LiteOn SOHW-1633S (2004-2012) and LH-18A1P (2005-2012)

While doing testing for the Milleniata post, I discovered that my two trusty quality test workhorses were dead. The SOHW-1633s suffered some (likely) combo chip failure and was unable to control its tray, or spindle motor. The LH-18A1P had consistent “No Reference Position Found” errors, consistent with the loss of the laser. With that quick diagnosis, I take a moment to salute these fine drives, and send them onto their way towards the garbage.

The LiteOn drives were extremely flexible, firmware wise, in terms of read-speed and write speed hacks, strategy re-labelling and swapping (through Omnipatcher) because of the big community that had built around guys at CD Freaks which included employees of LiteOn themselves. Through this, we gained access to diagnostics, for C1/C2 and PI/PIF/PO testing (using KProbe), Beta, Jitter and TE/FE testing (through DVDScan). With the EEPROM Tool, we were even able to overclock these drives – i.e. turn my 1633S into a 1653S, and my 18A1P into a 20A1P. This allowed us to gain speed, free of charge, courtesy of a few bit-twiddles. Unfortunately, more modern LiteOn drives don’t share the traits of these older veterans – they do not have the same quality test features and report results which appear to be less accurate.

They were my drives of choice when it came to testing. But their write quality often left a bit to be desired, as did their “long time” DVD-R lead-in bug which caused some drives to detect DVD-R’s written by their drives as blank. But the community support always pulled through, and these were also some of my favourite drives when it came to overspeeding media such as the RICOHJPNR01 4x discs which would faithfully burn at 8x, everytime.

It is a little known fact that LiteOn drives were actually OEMed for Sony – the firmwares for some drives could be “cross-flashed” to turn your LiteOn into a Sony and vice-versa. Later in their lives, LiteOn and Phillips joined forces to form PLDS – Philips Lite-On Digital Storage, to take on the “other alliances” – HLDS aka Hitachi LG Data Storage and TSST aka Toshiba Samsung Storage Technologies. Through this, their drives inherited some of the features (the ribbing on the top surface – that was introduced on the BenQ Philips DW1640 first as a way to keep the airflow inside the drive quiet and to harness it for cooling).

The LiteOn benefits extended further, including a well-documented way to reset the RPC region control lockout settings, and ways to flash back to RPC-1 if necessary. I will sorely miss these drives, but that being said, laser failure seemed to be a common trait amongst many LiteOn drives – the fact mine have lived such long and productive lives is something to marvel at on its own.

As these drives have, as a condition of me purchasing them, given consent to become organ donors, or to donate their bodies to science, what follows is a peek inside one of the drives just so everyone knows what lurks inside a modern optical drive. Unfortunately, given the “system-on-a-chip” nature of these drives, there is not much that can be re-used.

In the case you’re following at home, you will need a paperclip, and a Phillips head screwdriver. How to open these drives? Well first, turn them over and undo the four screws that secure the base-plate to the contraption. Remove the base plate.

This is the underside of the drive. You will see the left is the front panel loader, and this normally contains a tray motor, some gears, a few buttons, a position encoder, headphone socket, potentiometer and an LED. This is connected by ribbon to the main board on the right. In this mainboard, the main SOC is mounted on the reverse side – what you see is the connectors on the right edge, the combo motor controller (for spindle, tray and pickup sled) and the buffer memory (from Samsung). Note the SONY silkscreen near the power connector – I told you LiteOn OEMed for SONY!

Use the paperclip to emergency-eject the tray, unclip the front bezel from the tray, then the body, and you should be left with the following:

Some drives have side clips, others don’t – but you can see one clip pictured above near the screw holes for mounting. You will need to depress both clips, and lever off the lid to see the innards. Done that? Good! Now you will be greeted with the main guts:

Directly in the middle of the photo is the lens and the main pickup assembly which contains the lasers and photodiodes which read and write your data. This is connected by a wide ribbon to the mainboard below. The main SOC is just peeking out from above the top of the flexi-ribbon. The assembly itself is mounted on smooth rails, driven by a stepper motor which is mounted below the sled. The whole sled including the disc spindle motor is mounted on a rigid metal frame which is secured to the plastic frame of the drive using anti-vibration silicone grommets – this reduces noise and vibration transfer to the case, but also ensures that the sled and spindle all vibrate in harmony with the disc to maintain good tracking at high speeds.

The top of the lid also reveals an item which is the spindle “cap” which clamps the disc to the spindle through magnetic attraction. Some of these contain ball bearings which make a wooshing sound when the disc spins up and down (common for LiteOn drives) which acts as a counterbalance against unbalanced discs (washing machines actually have something similar as well!)

And here’s the actual SOCs responsible for almost everything – two Mediatek chips (very very common, aside from the NEC/Renesas, Panasonic and Philips chips which are the main competitors).

You will also see the flash chip with the firmware, covered with a label that has the initial firmware revision the drive shipped with – BS06. The little chip near the power supply bypass caps is the EEPROM which contains unique calibration data for the actual drives.

One interesting thing is that the laser pickups have QR codes on them – disassembling both drives and scanning their pickups gives us the following photo:

One of them is the serial number, the lighter colour one appears to provide calibration data – possibly to do with skew angles of the laser focus. The data from the left one is (0.06/-0.11/ 9.2/ 0.01/-0.03/ 5.5). The data from the right one is (00JGBE/- 2.7/+ 0.0/+0.01/-0.01).

So there we are – a look into the innards of a dead optical drive.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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3 Responses to An Obiturary: LiteOn SOHW-1633S, and LH-18A1P

  1. Johnny says:

    Hello, I know you wrote this “obituary” a long time ago, but do you know maybe which of the two potentiometers is for adjusting the DVD laser? I have an old LiteOn DVD RW drive (with working lasers) but it won’t read DVD+R media.

    Thanks for any help!

    • lui_gough says:

      I’m not sure how you know the laser is working, it could well be that the laser has failed as it often does of drives of this vintage.

      If it reads DVD-R and not DVD+R that has been written by other burners, let me share an observation that I’ve had. Most of my Lite-On drives, ending in 2S, 3S and 5S will not read any DVD+R that have been burnt by other burners with Philips or Renesas/NEC chipsets. It was something I had noticed and it drove me nuts, which is why I always had two burners – one Lite-On, and one non-Lite-On.

      Unfortunately, I cannot tell you which potentiometer does what – they could be power, focus, tilt or something else altogether. I have no idea, but if somebody does, please do go ahead and write a reply.

      – Gough

  2. Johnny says:

    Thank you for sharing your findings.

    I have been able to fix the non-reading issue of my drive. I was sure that the laser is working because I was seeing the red laser light (not directly, of course :)) when the drive was reading (or trying to read) DVDs. On the other hand, the CD laser emits in infrared which is invisible, but reading CDs worked, so it wasn’ t important to check.

    I fixed the drive by tweaking the two potentiometers: I figured out that if I turn one potentiometer clockwise, the drive stops reading CDs; if I turn it counter-clockwise, it reads CDs again. The other potentiometer worked the same, but for reading DVDs. I have to emphasize that the tweaking was done in very small steps. And in the end I have a working drive again.


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