One day in May 2020 we found a bargain on a non-working Philips VLP-700 on Ebay and couldn't resist getting it. This is the earliest laserdisc player released in Europe, which is based on the Magnavision VH8000 made for the American market. Magnavox was already a subsidiary of Philips at the time and the two models are more or less identical. We thought it would be fun to own one of these early machine to see if we could get it working.
We understood even before receiving the player that it would probably not be an easy to fix to get it running, but all the more fun. Opening the package up the player looked as if it has been in a shed for forty years, which it probably had given the smell of mold and overall dustiness, inside and outside. The drive belt had deteriorated and the laser itself was loose. Also, one of the vinyl gears for the slide drive was broken. We played with it for an afternoon but quickly gave up and realized we would need another player for parts.
We found two other players, both VLP-600, on Ebay quickly thereafter, and decided to buy one of them. We accidentally bought both. The VLP-600 and VLP-700 are the same players, the only difference being that the latter has a remote control. They were both in much better shape than the VLP-700, but unsurprisingly the drive belts for the slide drive had deteriorated in both. We tried using rubber bands but that just didn't work, so we bought a mix pack of drive belts on Amazon and replaced the belts in both VLP-600 units. Of course this wasn't the only problem. One of the players made a high-pitched noise that seemed to originate form the lens, so probably related to focusing. The other player actually focused and we got a picture: black and white and constantly fast-forwarding uncontrollably. We got both players to the same state by switching out the focus module replacing it with the one from the VLP-700. We had numerous other minor problems along the way, such as intermittent short circuits, bad capacitors, and bad connections.
After this we didn't have much progress at all: we did the usual troubleshooting: checking supply voltages and other common problems, but found nothing more to fix. We started to suspect that the optical components needed adjustments, but had no idea how to proceed.
We had a hard time finding the service manual, but early on bought Sams photofact for the Magnavox VH8000. Sams technical publishing produces third party service manuals. It turns out, that even if the players are very much alike, there are also a number of important differences. For example, the power supply board has been completely redesigned in the VLP players. Also, the numbering of the modules changed from the Magnavox to the Philips players, even if most of the modules themselves are identical. Most important, Sams photofact for the VH8000 doesn't have any instructions for adjusting the optical components.
To find the actual service manual for the players, it helps to know that the players were also sold as the 22VP600 and 22VP700, respectively. As soon as we knew we found service manuals easily, and even managed to obtain an original manual from Ebay.
We found that the Dragon's Lair Project has a lot of information about the repair of a few laserdisc players, one of them being the Philips 22VP931/22VP932, including service manuals. The optical path of these players is very similar to that of the VLP-600, even if the electronics are more modern. This is where we started to understand what the different components do, and how to adjust them. A critical step in fixing the players was to realize that the servo mirrors were all in need of service, and there is an excellent guide at the Dragon's Lair Project site for fixing them.
In order to check if the mirrors work, what we did was to apply the signal from a signal generator to the coils with the laser turned on, checking if the light spot moves. Looking at the schematics we deemed it safe to apply about 5 V, which is more than enough to move a working mirror about.
To check for movement, we followed the setup procedure for optical path alignment form the service manual. This involves taking out the tangential and radial modules, disconnecting the turntable drive, disconnecting connector A32 that connects to the mirrors, and connector A33 that connects to the slide drive and focus. Then, powering up the player turns on the laser beam so it is possible to check what happens in the optical pathway. To see the laser beam exiting the pickup, however, the lid needs to be open, and the player needs to be tricked into thinking the lid is closed. We never managed to understand the explanation in the manual for how to do this, but found two simple solutions: either force the lid switch closed by duct tape, or disconnect C07 from the power supply board and put two jumpers in its place.
Applying the 5V signal to the proper pins on A32 should move the light spot coming from from the pickup. Putting a paper in front of the pickup makes this easy to see. Since the alignment procedure requires taking off the objective lens anyway, we did this and the light spot is even easier to see since it is projected at a greater distance. The signal applied in the videos is a sine wave at about 2 Hz. Notice that in the first video, the spot almost doesn't move at all when applying power to the radial mirror, and in the second video, applying power to the tangential mirror, movement is jerky.
Each mirror has two cuboid-shaped permanent magnets attached at the back of a glass plate. It turns out the glue Philips used turns to goo after a long time, and thus the magnets drift from their intended positions. The magnets were slightly out of place, and the fix, all according to the Dragon's Lair guide, is to re-glue them. The guide uses epoxy glue, but as described there is a problem keeping the magnets in place while the glue dries. We used regular super glue instead and so far it works.
Commenting on the otherwise excellent guide, it says that if you forget the orientation of the magnets, it is basically the end. However, we did exactly that, and realized that this is not the case (so we didn't need the Doug Jeffery prescribed mallet). You need to realize that all the magnets are oriented with their poles in the same directions, and knowing that, it is quite easy to check how to place the magnets as long as you have a mirror with the magnets correctly oriented. See this video that shows a handheld magnet attracting the magnet of a mirror when close.
After fixing both mirrors, reapplying 5V to them shows that they were indeed fixed: see videos of one mirror working, and the radial and tangential mirrors in action once in place. For reference, a 5V peak-to-peak signal applied to a good mirror makes it tilt about 1/20 radians, peak-to-peak.
Now the optical pathway had be be realigned. The service manual, which by the way is excellent, explains how to do this, but the procedure requires some special equipment which we deemed unobtainable. Some of the items are a magical box, which Philips calls a "control box", which we think is a preamplifier with special outputs, and a "pupil filling meter". Since we had to do without these items we had to figure out what they actually do.
The first step is to use the "mirror alignment tool" to adjust the tilt of the mirrors. From what we guess, the point here is to make the beam hit the disc perpendicular to the disc surface when no control signal is applied to the mirrors. What we can do without the special tool is to make sure the beam exits as straight as possible. We did this by making sure the player was perfectly level; we used Hook Norton beer coasters when doing this but we're confident any brand will work. A laser level can then be used to find a spot in the ceiling exactly above the objective. If the beam is straight it should hit this point. Re-adjusting took some time since we had to open up the player and re-do the leveling between successive adjustments.
The next step is to adjust the spot lens. The service manual describes how to use the pupil filling meter for this purpose. Since we can only guess what such a device actually does, we started turning the adjustment screws to see what would happen. It turns out the adjustment itself was obvious once we started messing with it: the aim is to adjust the spot lens so that the beam hits the center of the objective, which makes the image of the beam a nice round full moon shape. When the adjustment is off, it looks like it is eclipsed. Of course, the pupil filling meter can probably help doing this more exactly, but just looking at the image projected on the white door trying to get a nice full moon worked just fine.
After this it is time to adjust the position of the photodiodes. For us, this was by far the most time consuming task—it seemed almost impossible to get the adjustments right. To understand the procedure we needed to understand what the adjustment does, and what the diodes actually look like: see the microscope picture taken from the side where the beam hits the diodes. The photosensitive areas are black.
The main beam hits the middle four diodes, and the auxiliary tracking beams are supposed to hit the two larger diodes. The player uses the sum of the four middle diodes for the HF signal. The service manual contains a nice description of how focusing and tracking works, and if you cannot find the manual, the process is exactly the same in the Philips 22VP931/22VP932, which we referred to earlier.
The player uses the signal (A+B)-(C+D) for focusing, so this signal is available to measure at the output of the preamplifier. The tracking signal, R1-R2, is also available for the same reason.
This is where the magical box is important: the instructions say to connect the diode output connectors to the box, which then outputs four signals: (A+C)-(D+B), A-C, D-B, and R1-R2. Since we do not have the magical box, we see two options: build a box, perhaps using the preamplifier from a spare player, or just try to make the adjustments using the signals we have available. We opted for the latter option but might try to build a box in the future since the adjustment is tricky.
To make the adjustment, we can measure what happens when the diode goes in and out of focus. This is the same general approach that is used with the box in the manual. In fact, it turns out we are going to look for more or less the same signals as referred to in that procedure, but of course we do not know what voltages to aim for when done.
We now need to set up the player so that the focus lens oscillates at around 20 Hz, while the beam is reflected from a non-recorded disc surface. We used side 4 of the PAL version of Prizzi's Honor, which accidentally happens to be the only PAL disc we own with analog sound. Actually we didn't have this at the beginning, so we used the front side of a CD, which works just fine using some masking tape. Notice the radial and tangential tracking modules need to be removed for this, as well as the turntable motor connector.
Basically, we want the focus signal to be zero when the diodes are in focus, with a nice curve indicating the direction of out-of-focus. Also, since we use a blank disc surface the radial signal R1-R2 should ideally be zero independent of focusing. This is achieved by moving the diodes using two adjustment screws.
Since the adjustment was quite non-intuitive to us, we wrote a simple simulation tool to understand the waveforms when out of alignment. Our very sketchy understanding of optics makes the tool quite inexact, but it did help us get on the right path to understand in what direction to move the diodes.
See pictures , , for some examples of oscilloscope waveforms when the diodes are misaligned, and also what they look like after calibration.
The final steps are adjusting the quarter-wave plate and the grating. The quarter-wave plate is what we understand the least. In theory, it turns the polarized beam from the laser into a circularly polarized beam, and when it passes through the waveplate again, after being reflected by the disc, the beam's polarization angle should be offset by 90 degrees. If the waveplate is out of adjustment, the beam will instead be elliptically polarized, and the resulting beam after passing through twice will not have the desired polarization properties. So, the beam intensity hitting the diodes should be at a maximum when the adjustment is right, since this is when the Wollaston prism deflects as much as possible of the beam towards the diodes. However, trying to adjust this seems to bring the diode adjustment out of alignment again, so we did not fiddle with it too much; for some reason things worked out anyway. Adjusting it just a little bit also makes the focusing noise from the machine vary. This is what the manual says will happen but we cannot really understand why. If someone knows what other effects this adjustment has, and how it affects focusing, then please let us know.
The grating adjustment determines how far, radially, from the center beam the two auxiliary tracking beams land on the disc surface. Again, the procedure in the manual is sound: first adjust all the way to the right, so that the auxillary tracking beam hit the same track as the main beam, the on-track position. Then, adjust so that the tracking signal is maximized. Actually, it worked fine to do this without measurements—just adjusting until the picture is stable, since the player skips a lot when the grating is off.
Finally, the player was working! However, the picture was black and white, but that was the monitor needing repair. Of course this is now fixed, but the VLP-600 had priority for a while: see this video with working color. Notice the lack of sound due to the disc being played is the French PAL version of Titanic, unfortunately with digital sound. So actually, the sound is muted since the player happily plays back the digital track as an analog audio signal, with obvious and unpleasant results.
With the player in working order we paint locked all the adjustment screws with nail polish to keep them in place!
We now have a fully working VLP-600. After re-assembly it was tested on the big screen. Since modern TVs are quite bad at playing back laserdisc content we used an external de-interlacing upscaler. As we show in the video, all functions of the player work correctly, including sound!. We use Prizzi's honor, this time side 3, which is CAV, to demonstrate all the trick play features of the player. There are some visible dropouts, but in general we are impressed with the playback quality!