What I've Learned Fixing Optical Drives

So You Want to Fix an Optical Drive

If you found this page looking for advice on how to fix an optical drive, you might be in luck.  There's a lot of information and prognostication out there these days that might tell you fixing a laser mechanism is a losing proposition, but the fact is that in many cases these drives are completely fixable.

Over the past decade I've begun fixing a optical drive failures in a wide variety of hardware. In the process I've learned a thing or two about a thing or two and I've compiled my findings here in the hopes they may help someone else.

Full disclosure: I'm a technical professional, just not in the field of electrical engineering.  I do this as a hobby.  My skills and information comes from a lifetime of curiosity and decades of reading manuals, reading books, learning from experts and practical application.

My success rate in repairing these drives and restoring them to original function seems to be in direct opposition to popular thought on the matter which is that these devices are essentially perishable and will fail simply due to age. 

While I can't account for all the reasons these theories are so popular, I have zeroed in on a couple of areas that definitely contributed.

• The popularity of "tweaking the pots" - which refers to adjusting the laser power level.  When people first discovered that adjusting the potentiometer that controls laser power seemed to get the drive to begin working again this information quickly propagated across the Internet and a good number of people tried it without proper tools or procedures because the tools were expensive and the procedures required a good understanding of complex tools. This was followed up by countless stories that the drive eventually failed again and no amount of "tweaking" would bring it back, creating the perception that once a drive starts struggling it's demise is inevitable.

• Published (or rumored) manufacturer longevity predictions.  Manufacturers of mechanical parts generally perform artificial aging to determine an operational lifespan rating. Taking these as gospel truth is essentially conflating narrow statistical predictions with individual real results.

• Every single ODE or similar device that has been released in the last several years has been accompanied by marketing (either direct or word-of-mouth) that you should buy it because your optical drive is on it's way out and soon this will be the only way you can play your games. This is marketing, not real life.
  

• Any number of addages or axioms about moving parts breaking down over time. While this is essentially true, it's intellectually dishonest to use it to estimate the life expectancy of a specific device without any actual data. It's also often misused to  imply that solid state devices last forever.  This is marketing, not real life. Anyone who's had to replace failed electrolytic capacitors in a device with an optical drive knows that the mechanical components outlived the solid state components.

While I do acknowledge optical drive formats are fading into obscurity and will continue to do so, this is really being driven by convenience, not by widespread reliability issues with the technology.  Most of these drives can and will outlast the widespread desire to use them.  

If you're seeking help repairing an optical drive in 2020 or beyond, you have very likely already encountered the hand-waving advice to not bother fixing the drive when you can just replace it with a modern solution instead.

In the last few years Optical Drive Emulators (ODE) or functionally equivalent hardware has been made available for almost every popular optical disc format.  These replace mechanical devices with solid-state devices which almost completely eliminate the possibility of mechanical breakdown, and at the same time allow users to contain an entire game library on a single storage device (usually an SD card).  While these are super-convenient, none of them are perfect.  As of this writing, none of them has a verified 100% compatibility rate, and many will play games but with degraded sound quality or other compromises. The important thing to remember is that there is always a trade off when you ditch the original drive for one of these modern solutions.  For some the trade off is worth what you gain, for others it isn't worth what you have to give up.

So why bother to maintain optical drives?

• They're still the only way to play original games (your collection of games on optical disc is useless without one)

• They're 100% compatible with their console's library (both in terms of being able to execute games and do it correctly)

• They're part of an authentic original experience

• The technology is cool and fun to work on 

Why "Tweaking the Pots" doesn't work

What the "Pot" is really for

To understand why adjusting the laser power isn't a long-term fix (well it isn't a fix at all, really), it helps to understand what the laser potentiometer is actually for.  In a perfect world, the device that powers the laser (i.e. the PlayStation motherboard) would be designed in such a way that it always supplied the exact amount of power the laser required to operate and we wouldn't need potentiometers. While this is technically possible by using the highest quality components, it's also not really cost effective.  The reality is that these devices are usually built with the most inexpensive components the manufacturer can get away with.  Components such as capacitors and resistors which control voltage levels can often have very wide tolerances - commonly 20% higher or lower than their rated values.  When these components are assembled into a circuit those wide variances can have a definite impact on the laser which requires a somewhat precise supply of power to operate correctly.  The laser potentiometer exists solely to dial in the laser at the factory to account for the inaccurate components the machine is built with.

Why Lasers fail after "Tweaking the Pots"

While it is possible that voltage drift from failing components (specifically electrolytic capacitors) could be to blame for a laser that gradually stops working, I have very rarely found this to be the case (i.e. never).  Most often the laser is failing to read because the lubrication has failed on the transport mechanism and the transport motor can no longer overcome the friction to seek properly. Increasing the power to the laser can temporarily alleviate this (for a number of reasons) but because the underlying problem is not being addressed it just gets worse until the power has to be turned up so high that laser breaks down electrically.

If I can be forgiven for a car analogy here, over-powering the laser when it starts to have trouble tracking is like pressing harder on the accelerator when you feel your car start dragging or struggling to move.  It does make the car continue to move, but without addressing the source of extra friction, you're just making the problem worse - grinding dry bearings, wearing down your cylinder walls etc...

How to Interpret the Manufacturer's Estimated Lifespan

Whether it's a car, a kitchen appliance, or an optical disc drive a manufacturer's estimated lifespan should always be read as "it will last at least this long", not "it will only last this long".  While planned obsolescence is a real thing, very few manufacturers intentionally sabotage their products to ensure they fail after a certain point.  In most cases the effort and risk would be disproportionate to any gains.

 

When a manufacturer estimates device life spans they do so using artificial test conditions to establish a baseline for what they're comfortable guaranteeing and they all make assumptions about "typical use".  

 

In the case of an automobile their estimates assume regular maintenance - if you don't change your oil when you're supposed to, keep your fluids topped off, use the right kind of gas etc..., your vehicle is likely to break down prior to when the manufacturer estimates.  

 

In the case of an optical disc drive you have the opposite assumption - they're not expecting that anyone is going to perform maintenance on them.  If you do, barring serious design flaws, your optical drives can greatly outlast any manufacturer's estimates.  Drives don't just magically fall apart and stop working after a certain amount of time or a certain number of operations, they stop working because they physically or (very much less likely to happen without help) electrically break down.

Laser Mechanism Common Elements

While there are differences from one device to another they basically all operate on a common set of principles and the mechanisms almost all feature similar elements.

Loading Motor

Drives with a loading tray, such as the XBOX, XBOX 360, PS2 Phat, Sega CD model 1, the 3DO FZ-1, The CDi-220, most PC drives and Laser Disc players all require a loading motor which is responsible for two things.  The first function is to open and close the disc tray.  The second function is to raise the spindle assembly (and/or the laser transport) into place after the tray closes and lower it out of the way before the tray opens again.  The loading motor is pretty much always attached to the loading mechanism with a "square" rubber belt.

Clamp

The clamp is the mechanism that holds the disc in place on the spindle motor.  Most commonly these clamps are magnetic, but they may also come in the form of spring-loaded bearings (such as the Dreamcast, PS1, PS2 Slim, PS3 Super-Slim). The magnetic clamps are either positioned above the spindle assembly in a tray-loading drive and locked into place when the loading motor raises the assembly up, or they're installed in the lid (such as on the Sega CD model 2 and the Turbo Duo) and pull into place when the lid is closed.

Spindle

This refers to the motor and apparatus which spins the disc.  Spindle motors are usually directly attached to the shaft that spins the disc (as opposed to being attached through gearing or belts).

Laser Transport

This is the mechanism that moves the laser pickup tangentially back and forth next to the surface of the disc.  It holds the laser pickup and consists of two "rails", a motor, an arrangement of gears to allow for precise positioning, and one or more "limit" switches.  The rails may either be cylindrical metal shafts (such as on the Saturn or PS2) or they may simply be grooves for the anchor points of the laser pickup to slide along (PS1).  The gear set almost always consists of a "worm" gear (long thing shaft that looks more like the grooves of a screw) and a straight gear-tooth piece of plastic either attached to the mechanism or the shaft to propel the gear back and forth.  With most 12cm (CD/DVD/BD) drives the laser transport and the spindle assembly are a single unit, but with LD players the laser transport usually moves independently of the spindle assembly.

Laser Pickup

The Laser Pickup is usually made from die-cast metal and contains both the laser diode and the photo sensor(s) which "read" the reflection of the laser.  The lens assembly "floats" above the laser diode and sensor(s), suspended between electromagnets which can raise, lower and tilt the lens.

Limit Switch(es) / Door Switches

Optical drives typically incorporate one or more "limit" switches. The transport limit switch(es) tells the drive when it has reached the end of travel so it can stop the transport motor from trying to move the transport any further.  Since CDs are normally read center-out, the limit switch will be positioned at the center limit of travel. When initializing the laser often doesn't even turn on until the transport has moved to the inward position.  

 

The limit switch(es) may be a leaf switch mounted below the transport on the drive PCB, or it may be a push-in style momentary switch on the laser pickup itself.  Although it's rare, there are sometimes limit switches on the opposite end of travel (towards the outer edge of the disc) as well. 

Tray-loading drives have a second limit switch which tells the drive whether the tray is fully open or closed, but these vary quite a bit in type and position. Sometimes they're positioned behind the tray, sometimes they're positioned next to the loading motor and activated by a peg from the loading mechanism etc...

Door-loading drives have a door switch which performs the same function of notifying the mechanism whether the door is open or closed.  These are normally located close to the door hinge, and may either be typical momentary switches, or leaf switches.

Suspension

Because optical disc drives deal with such precise movements they're very susceptible to external vibration.  Almost every optical drive has some sort of suspension whether it's metal springs (like the Sega CD Model 1) or rubber shock absorbers (Playstation, Sega CD Model 2) which are designed to "disconnect" it from surface vibrations.

Common Optical Drive Function

To understand some of the failure states you might find, it helps to have a basic understanding of how an optical drive laser mechanism normally operates.  

 

Tray Loading

When you eject a tray-loading mechanism, the spindle motor first pulls the spindle (and and usually the laser transport) downward out of the way of the tray, then it ejects the tray.  When you load, it performs these steps in reverse.  When the tray is fully inserted the spindle motor is raised so that the spindle shaft slots into the hole in the center of the disc and raises it into the magnetic clamp.  The action of closing the tray also triggers a limit switch which informs the drive the disc is ready to be read.

Door Loading

Door loading drives either clamp the disc with spring-loaded bearings on the spindle itself or a magnetic clamp in the lid of the drive which pulls into place when the door is closed.  When fully closed a door switch is triggered to inform the mechanism that the disc is ready to be read.

 

Initializing

When the drive is closed the spindle will engage and spin the disc, while the laser transport will move the laser pickup toward the center of the disc and attempt to read the "lead in" area of the disc.  It finds this by moving the transport mechanism towards the center until it strikes the limit switch.

Reading

In order to properly read information from the disc the beam must strike the surface of the disc at almost exactly 90 degrees and be at the proper distance to precisely focus the beam onto the surface and back to the photo sensor.  Since it's nearly impossible to manufacture optical discs at scale which are perfectly flat and have perfectly round tracks, the laser pickup is designed to be raised and lowered and tilted inward and outward by tiny electromagnets in order to keep the beam perpendicular to the tracks on the reflective surface despite the disc's imperfections.

 

Seeking

As the laser mechanism processes instructions for seeking to different areas of the disc, the transport mechanism moves the pickup tangentially along the surface of the disc and the pickup takes periodic readings looking for position markers, or addresses.  When it finds the address it needs it begins reading the rings of the disc. The transport mechanism by itself is not precise enough to move the laser exactly where it's supposed to go, or at the exact rate it needs in order to continue smoothly reading data, so it works in tandem with the tilt mechanism of the pickup assembly, using the transport for larger movements, and the tilt for smaller ones.

 

Common Optical Drive Failures and Solutions

This section will cover failure states which occur during normal use. Drives can also fail because of abuse like "tweaking the pots" to the point the laser diode burns out, or physical damage from shipping or accidental drops.  Electrical failure due to improper adjustment is generally unrecoverable.  While I've had good success restoring physically damaged drives, the process varies so widely it would be difficult to reduce an article describing the possibilities to a digestible size.

Lubrication Failure

Symptoms:

• Audio or FMV skipping

• Persistent rapid seeking noises (re-reads)

• Long load times

• Unable to load

• Have to turn the machine on its side or upside-down in order to load normally.

• Not recognizing a disk is inserted

This is the VERY FIRST thing you address when experiencing general optical drive problems and there is no other very obvious cause.

The moving parts in a laser mechanism are generally lubricated with white lithium grease or a similar lubricant which is safe for both plastic and metal parts, but these lubricants all break down over time. Lithium grease tends to separate over time (decades) and no longer help with friction, other greases tend to harden and some even add friction by becoming sticky.   Additionally pet dander, dust, hair, food particles and even residue from tobacco smoke which find their way inside the mechanism will stick to the grease and reduce its effectiveness.

Spindle motors are usually lubricated with oil which is unlikely to break down, but it can gradually succumb to friction and gravity, and more than once I've found long hairs wrapped around the shafts.

Properly re-lubricating a laser mechanism requires that you first thoroughly clean out the old lubricant. Simply applying new lubricant on top of the old will likely just introduce a new source of friction rather than fix anything.

To properly clean a laser mechanism, it has to be carefully disassembled.  This varies enough from one to another that I can't reasonably provide step-by-step instructions, but I can offer a couple of tips:

• Never touch the lens

• Consider wearing gloves to reduce the impact if you accidentally touch the lens.

• Use tweezers to pick out fuzz hair or other large debris from anywhere in the mechanism.

• Go slow and be gentle. These mechanisms are meant to come apart but sometimes it's not obvious how.

• Consider taking pictures as you disassemble.  It should be very obvious how everything goes back together, but taking pictures is cheap peace of mind.

• The transport mechanism should be disassembled completely, but at a minimum the laser pickup needs to be completely separated from the rails.

• You don't necessarily need to take all of the gearing mechanisms apart, but you definitely need to separate the laser pickup from the rails and remove enough of the gearing that you can get at all every surface with a toothbrush.

• It should be possible to advance the gear mechanism by turning the worm gear on the motor with your finger - you'll want to do this to make sure you can move the gear teeth around enough to get all of the old grease off. 

Once you have the laser mechanism disassembled you'll want to use a combination of a toothbrush, cotton swabs and a plastic-safe solvent to remove all of the old grease from the rails, the contact points on the laser pickup, and all the gear teeth.  I recommend VM&P Naptha (which is basically lighter fluid).  In a pinch 90% isopropyl alcohol works too but it can technically make plastics more brittle (though I think that requires much more exposure than a quick scrub with a toothbrush is going to cause).

For re-greasing all of the moving parts, I like to use a cotton swab snipped in half at a sharp angle so I can use the stick part as a little precision applicator.  

Use white lithium grease for all of the metal and plastic parts (except the spindle motor).  Rather than applying grease directly to the rails themselves, I recommend putting a small dab of grease on the points where the laser pickup contacts the rails, and let the pickup transfer the grease to the rails. I find that if I start by placing the trasnport at one end of travel and slide it to the other, the grease will wear off about half-way through so I re-grease the contact points and start at the other end and repeat until there's a thin layer of grease all along the range of travel and the pickup slides smoothly and evenly.  

To lubricate the gears you want to make sure the entire length of the worm gear has a thin coat of lithium grease, and just a light amount on the other gear teeth.

The spindle motor and shaft require a somewhat different approach.  First you want to turn the spindle motor by hand. It should turn very easily and smoothly. If it doesn't turn easily or it feels like something is grinding, don't keep turning it - find out what's jamming it up before continuing. Check for debris or hairs near the shaft and either clear it out with a long-bristled brush, compressed air or tweezers. I DO NOT recommend removing or trying to remove the spindle cap from the motor shaft.  Once the shaft is clear and clean, use a precision needle oil pen to apply a drop of sewing machine oil right where the shaft goes into the motor housing. (I actually use a product called "Prolong" for this but sewing machine oil should work fine too.)

Once it's all back together, use a cotton swab dipped in isopropyl alcohol to lightly touch the laser lens enough to wet it, then use the dry side of the swab to gently clean the lens.  It's normal for the pickup mechanism to wiggle a little as you're doing this but be extremely gently as applying too much force can stretch the delicate springs that suspend it.

Laser Transport Limit Switches

Symptoms:

• Drive makes brief grinding noises but seems to work anyway

• Drive makes constant grinding noises and won't load

• Drive makes constant motor noises but can't load

• Pickup assembly rapidly "bounces" toward the center of the spindle 

There are two main styles of limit switch - the first is usually a momentary switch mounted on the laser transport (ex PS1, LD Players).  These rarely go bad or require attention, but you can easily check their function with a multimeter continuity test.  Press the "button" and make sure it completes the circuit properly. If it doesn't have good contact this can usually be addressed by spraying some Deoxit into the switch mechanism and pressing it in a few times.

 

The second style of limit switches are leaf switches and they're normally mounted on a PCB underneath the transport mechanism - easily identifiable because they're usually a clear plastic box with long thin strips of copper inside.  These are far more prone to have problems. They usually fail because they're either bent, or on rarer occasions, oxidation has increased the resistance at the contact points.  They sometimes become bent away from the laser transport under normal use and this is when you get the grinding - because the laser transport doesn't "know" that it's gone as far as it can and it keeps turning the motor causing the gear teeth to skip.  These can be extremely fiddly to fix because it's hard to gauge where they're actually supposed to be.  You can tell whether they're too far away from the mechanism (grinding) or too far away from the mechanism (bouncing), but getting them bent back into the right position involves a lot of trial and error.  Since the switch is essentially a flat spring you have to press it quite a far in the right direction to actually begin to put a permanent bend into it. If you don't push far enough, when you let go the switch will just return back to its original position. If you push too far, then you may make the situation worse.  You just have to go slow, make the smallest permanent bends you can then check and repeat until the grinding or the bouncing stops.

Loading Tray / Door Limit Switches

Symptoms:

• Open/closed status reported incorrectly (says "open" when closed or vice-versa)

• Disc doesn't spin when tray/door is closed

• Disc tray randomly opens or closes

• Have to close the tray multiple times before it will stay closed (this may also be a symptom of a worn belt).

The push-in style limit switches and door switches very rarely have problems, but they're subject to oxidation, contaminants and material breakdown just like anything else.  On a tray-loading drive, to find the limit switch, look for wires going to anything that isn't the loading motor and isn't the laser transport.  Sometimes the loading motor will be driven by a small PCB, and you'll occasionally find the tray limit switch there.  Use a multimeter continuity setting to check if the switch easily completes a circuit when pressed.  I've only ever found one that was having trouble, and a shot of Deoxit and pressing the button a couple dozen times cleared it right up.

Leaf style door switches often have the same problems that all leaf switches are prone to - they tend to lose their original shape over time and need to be gently bent back into place.  Some of them are in a position prone to get bent by accident - such as the Sega CD Model 2 where it's very easy to damage the door switch if you aren't paying close attention to it when you try to re-assemble the drive.  Fortunately it's much easier to get these bent back to shape when they're on a door switch because they require less precise positioning.

Worn Belts 

Symptoms:

• Failure to spin-up (no sound of the disc spinning) when the tray closes because the spindle assembly isn't being raised into place.

• Reporting no disc in the tray (this is rare but it does happen depending on the drive controller logic)

• Endlessly opening and closing the disc tray (Sega CD Model1)

• Disc tray will not eject (XBOX consoles with a Thompson DVD drive) because they cannot overcome the clamping magnet well enough to pull the transport down and out of the way.

Over time the heat, oxidaton, temperature and other environmental conditions will cause the belts on the loading mechanisms to fail.  They can fail in a variety of ways.  Most commonly the belts simply lose tension over time and start slipping when thee tension is no longer enough to overcome the friction of the loading mechanism. Sometimes belts slip because they've hardened from lack of use causing the belt to become rigid and its surface to become smooth and lose its grip on the pulleys.

Obviously the best solution is to simply replace the belt.  The good thing is that square drive belts are super common and you can find literally hundreds of sizes.  The tricky thing is that there is often little to no documentation about what the correct belt size is for a given drive, either because there's no documentation, or the documentation refers to a defunct part number.  Measuring drive belts is kind of tricky to get right, and if the original belt has loosened you can't rely on its current size as the correct size.  If you install a belt which is too large it may still slip and fail to load right away or it may work for a short while before failing again. If you install one which is too small it will put more physical resistance on the motor and pulleys which may cause premature failure of the motor and/or the capacitors which drive it.  Thankfully places like Console5.com maintain a good supply of purpose-specific belts.

 

Split Gears

Symptoms:

• Clicking sounds

• Failure to load

• Disc loads but then freezes

Over time environmental conditions and design flaws can cause the gears in some transport mechanisms to split. This can cause the laser transport to fail when it hits the gear tooth where the split is because rather than advancing the gear, the force simply separates the gear at the split point.  This is common in 3DO FZ-1 consoles, but does happen in others.  In all the time I've been doing this I've never seen anyone successfully repair a split gear.  When this happens they simply have to be replaced.  It's often difficult or impossible to source the exact gear needed.  Occasionally you can find a "donor" drive which shares the same transport mechanism, but any time you employ used parts it's hard to know how long it might last before failing again.  Thankfully the prevalence of this problem and the advent of 3D printing has led to the availability of replacement gears for some of the more popular mechanisms.  Again Console5.com is a great place to start looking if you find this particular problem.

Collapsed Suspension 

Symptoms:

• Scraping or scuffing sounds

• Ring patterns scratched into the underside of discs

• Skipping audio or FMV

While the primary purpose of the suspension mechanism in an optical drive is to dampen external vibrations, these components also commonly add height to the laser transport and spindle.  As they collapse, they sink, eventually bringing the surface of the disc into contact with the tray or the laser transport.

There are two basic styles of suspension: metal springs (Sega CD Model 1) and hollow rubber grommets (Sega CD Model 2, Playstation 1).  

Metal springs can be restored by gently heating the metal (such as by boiling the in water) to allow the springs to relax back into their original shape.  It may be necessary to physically stretch the springs back out, but do this with extreme caution because it's very easy to accidentally go too far, and it creates greater fatigue.

The rubber grommet style shock dampeners generally can't be repaired as they usually crack and split and generally disintegrate as they collapse.  Replacements can be very difficult to source for some of them.  In the past for the ones I've not been able to source I've resorted to using weird substitutes like foam ear plugs, earphone plugs, and shock damper "balls" designed for custom built drones. You shouldn't worry too much about the shock dampening abilities of the material so much as raising the laser pickup and spindle back to the correct height.

Electrolytic Capacitors (Failed OR Replaced)

Symptoms:

• Disc spins but can't load

• The system indicates "no disc"

• FMV or audio skipping

• Issues with other parts of the device (i.e. reluctant to power up, video artifacts, poor quality sound, low volume etc...)

• Drive seemed to work better before capacitor replacement.

As electrolytic capacitors fail they tend to unbalance circuits and this can cause seemingly random unpredictable behavior. This is especially true in digital circuits where the difference between a one and a zero is determined by voltage levels.  While this tends to affect other functions such as video and audio before it affects optical drives, it definitely can prevent the optical drive from performing properly.

Whenever you start having trouble with an older piece of hardware and there is no other obvious cause, it's a good idea to check and/or replace the electrolytic capacitors as this can address a huge variety of problems, including optical drive issues.

On rare occasions, after you have replaced the capacitors in a piece of hardware in order to address other issues, the optical drive may actually perform worse afterwards.  This can happen because of differences in component tolerance.  The new capacitors may have significantly changed the voltage levels being delivered to the laser pickup.  If the electrolytic capacitors have been replaced AND the drive has also been cleaned and re-lubed AND you're still having problems reading discs, this is the one scenario where it's a good idea to bust out a service manual and an oscilloscope and adjust the laser.

Proper Laser Adjustment

As you're probably aware all optical drives work on the principle that a laser reflected off of the surface of the disc will land in one of two positions on a photo sensor.  This is achieved by creating "pits" and "ridges" on the reflective surface. For digital for formats these values are evenly spaced and represent binary values.  For Laser Disc these "on" and "off" positions vary in "width" and represent an analog waveform.  

 

In either case the position is read by the reflected laser striking the sensor and causing an increase in voltage when a "1" and decrease when a "0".  In a perfect world, the sensor would always be completely dark for "off", and completely lit up for a "on", however even laser light scatters somewhat, so at any given point both the "on" and "off" positions will detect some light, thus the voltage will actually rise in both.  In order to be able to distinguish between the two "on" and "off" are represented by a voltage threshold.  The logic isn't simply "voltage" is "on" and "no voltage" is "off", rather "voltage above such-and-such" is "on" and "below" is "off".

When you change the amount of power being supplied to the laser, you are increasing the intensity of the beam and consequently the voltage by which it raises the sensor.

 

Why You Need a Scope

What you're actually trying to measure and adjust when you look at the signal coming from an operating laser pickup is the difference between the highest and lowest voltage as the signal alternates between "off" and "on".  Since the lowest voltage isn't zero, and even the slowest CD drive is reading at least 150,000 bytes per second, you can't really capture this with simple tools like a multi-meter.  This difference between high and low voltage is called "Vpp" or "voltage, peak-to-peak".  Getting this measurement requires an oscilloscope because Vpp really requires the ability to visualize the waveform.

The only reliable way to know what Vpp should be for a given laser pickup is to find it in a service manual. Service manuals also help you to locate the correct test points to attach the oscilloscope.  

 

When you attempt to adjust laser power without a scope, you may find a spot where the drive happens to work well, but if you haven't actually dialed in the correct Vpp, the drive may still have problems.  Turn this up too high and the laser may seem to work better but it won't be able to cool itself properly and may thermally break down. Don't turn it up high enough and it may only work at the center of the disc and not at the outer edge.  A scope is really the only way to know whether you've really succeeded.

 

Adjustment recommendations vary a bit between drives which is another reason it's important to consult a service manual if at all possible.  Official repair centers were sometimes provided with special test discs to assist with adjustments by providing easy to recognize test patterns and deliberately moving the transport to the outer edge.  Because these discs are not widely available, even with an oscilloscope it sometimes takes a bit of work to dial the drive in correctly.

 

Lost Causes

In the approximate decade I've been doing this I've run into exactly two optical drives I was unable to restore to function.  

 

The first one was a Pioneer Laser Disc player which suffered from an electrical failure I was unable to successfully diagnose because I have never been able to obtain a service manual.  The drive mechanism itself works perfectly (I temporarily transplanted it into another identical player during troubleshooting).  If I ever figure out what's wrong with the player's motherboard I expect a full recovery.

The second was from a SCPH-1001 Playstation. The optical drive in the first generation Playstation 1 was so cheaply made that both the contact points on the laser transport and the transport rails were made from plastic. The plastic-on-plastic contact combined with close proximity to the heat of the power supply meant that the plastic was both pliant and the lubrication failed prematurely. As the rails and the transport broke down the surface became pitted and the transport motor can no longer overcome the friction to move the transport into position properly.  I was able to get the drive functional again by polishing the contact points, but the plastic didn't polish well and the drive still struggled and was generally unreliable.  I have kept two other SCPH-1001 units functioning normally with their original drives by performing a little preventative maintenance.

 

Sony fixed this design flaw and later PS1 revision lasers with metal contacts on the laser transport, and in the console itself by positioning the laser assembly further away from the heat of the power supply. 

 

Incidentally my success rate fixing post SCPH-1001 lasers is so far 100%.  I have a small stack of brand new replacement PS1 laser assemblies that I bought expecting I would need them, but so far I've only ever needed the one.  All of the other consoles are running with their original drives.