Philips LaserVision

Have you seen this thread? These players are after my time in the trade so know nothing about them.

https://www.radios-tv.co.uk/community/vintage-vtr/1982-philips-laservision-vlp-600/

Thanks, I've seen the thread. Actually I posted this as a followup to that thread, and that's the reason for the first sentence, but apparently the moderator thought a new thread was better.

I finally got a good belt for the slide drive (bought a mix pack of 50 rubber belts from Amazon and tried different sizes). It seems the motor is good after all in two of the machines -- the third one is dead. So, the best working unit now starts by spinning the disc and moves the optical assembly to the start. Maybe the starting position needs adjustment: if started at that position, the player never seems to read anything and it just starts and stops the turntable motor without doing anything else. If started in the middle of the disc, however, it seems that it starts to read something on the way back (the optical assembly starts making a sound), and it then starts playing the disc when returned to start.

Playback is very poor, however: the optical assembly moves too quickly over the disc, as on partial fast forward. At the beginning, the disc seems to spin at approximately the right speed since the picture at least is synched vertically (but again, mixing several frames in one due to forward skipping). Further into the disc, it seems the turntable doesn't have the correct speed since the picture starts rolling and it looks as if the picture is compressed vertically. 

Also, of course there is still no color and sound is noise only. Strangely, chapter information is correct.

I've found +12 V and -12 V power, and both seem fine.

I also had a quick look at the RF signal from the pre amplifier and it looks very noisy -- not much resemblance to the pictures in the service manual.

While I don't have any hopes it will magically fix everything, I'll probably wait until I get the PAL CAV disc I ordered from ebay before continuing.

Staffan

Long time without any news but I've been working on and off on these players and picked up some information. I still do not have one working, but now two of them are at least in the same state, i.e., skipping b/w picture with noise for sound:)  Still waiting for the CAV laserdisc -- the postal system isn't what it used to be. I also now have a copy of the service manual -- it helps to know the VLP-600 is the same player as 22VP600. Long post ahead -- maybe it can give some ideas to someone else working on the same player.

I determined that the servo mirrors were all bad. Applying power using a signal generator make them shake a little bit but that's it -- one of them moves one direction only. So I tried following the instructions at http://www.dragons-lair-project.com/tech/docs/firefox/fix.asp  about fixing another Philips LD player that is very similar in the light path construction, the 22VP931 (electronics is a few years newer, however), and successfully fixed the two mirrors in one of the players (I still haven't touched the one that worked the best to begin with but I will need too -- one of its mirrors is also stuck).

After doing my best at aligning the light path this player gets to the same state where the best working player was to begin with. I'm quite confident there is more to do in the way of adjustment, however.

So, I do not have the special tools or the test disc referred to in the manual, but I did this (numbers correspond to the adjustment procedure in the manual):

pre 1. Adjusted the disc to be parallel to the upper metal plate of the player -- there is an adjustment screw next to the motor to tilt the disc. I'm not sure but I think I had more problems in the following when that was not the case. I used the depth rod of a caliper to measure the distance from the upper side of the disc down to the plate.

1. Radial and tangential mirrors.  I believe what is done here is simply to make sure that, when there is no power to the mirrors, the beam points straight up. I leveled the player (its top plate), removed the objective lens and powered the player on (without thes servo modules, and with the motor and focus drive disconnected), so there is a red spot in the ceiling. About 2 meters up the spot is about 10 cm diameter.  I then used a cross laser to make sure that the spot was exactly above the exit pupil. (One needs to check from two directions, and when it is off, adjusting is a bit awkward since I can't really adjust when the player is standing flat on the table, so this took some time with a few power on-check-power off-open up and adjust-cycles.) I was finally happy with the result.

2. Spot lens.  I had a hard time trying to understand what the purpose of the procedure is. However, again, with the objective off, looking at the light spot (this can also be done with the objective in place) and turning the adjustment screws for the spot lens, the purpose is clear, and I believe adjusting this by eye should probably work. (Basically, when off, the intensity is skwed in the visible spot, so it looks like a half moon; when correct, it looks like a full moon.)

Looking at the projected image in the previous steps also shows if there is debris in the light path. I had some large dark bits in the image that disappeared after blowing CO2 at some optical paths (well -- that's what I had at hand that I thought would be clean and inert).

3.Diode. This is the tricky part. The first part that's tricky is understanding what the different screws do. The manual says to adjust two of them, while the other two supposedly just holds the photo diode array assembly in place. It is clear that the rightmost screw does just that. However, I found that the second screw from the left can be fastened so that the two other adjustment screws have different adjustment envelopes. I could be wrong here, however. 

This is the approximate diode layout -- the letters are actually different in different parts of the manual which is confusing, but this is the layout.

E

A B

D C

   F

According to the manual, use a special service box to get the following signals from the photo array: (A+C)-(B+D), B-D, A-C, and E-F.

The first of these signals, (A+C)-(B+D), is the focus signal, and E-F is the radial offset signal. Since these are outputs from the pre-amplifier we can measure them also without the magical box. I have no idea about their relative amplitudes, however -- the amplifier in the box might do something different than the pre-amp in the acutal player. B-D and A-C can be used to position the sensor too, and while I'm sure it would be nice I hope they are not necessary. 

The problem is that the signals before the pre-amp are very weak: I get nothing but noise if I try to measure them directly. I've been contemplating building a small switch box to put in front of the pre-amp to get to these signals too but haven't got around to do that yet.

Anyway, using the procedure as described in the manual (laser on, servos disconnected, motor disconnected, slide drive disconnected, focus coil connected to a signal generator, using the outer rim of an 8" test disc instead of the unrecorded side of the Philips test disc -- a mirror can probably also be used but it has to be fixed in the right position somehow; using an 8" disc makes it possible to place the laser close to the other edge), I've spent quite some time trying to make the focus and radial signals look like the pictures in the manual. I discovered that opening up the third screw that holds the diode to the metal assembly (not part of the official adjustments), helps to place the diode horizontally. The best I got to has about a 1 V p-p focus signal and the radial signal at a few hundred mV close to the focus area. I'm not sure if this is good enough. Will post pictures of the scope later but I don't have them here.

The manual says the radial signal should be very small compared to the focus signal, but then again I'm not sure the amplifications are comparable.

After making these adjustments the player does focus when turned on. However, it still doesn't quite work: it moves the slide drive to the start of the disc and stays there. I think this might be a small adjustment problem: moving the slide manually a few mm does start to play the disc (probably the stop has to be adjusted so that the lead-in track is just under the end of the range). However, picture is b/w, and the player fast-forwards constantly. For some reason it turns off completely after reaching about half of the disc, but I'm thinking that could be any unrelated problem.  

So, the next steps:

4. Quarter-wave plate 

and

5. Grating

cannot really be performed since they require a stable picture. Again, hopefully a CAV disc could show less problems -- need to start finding another disc than the one I ordered.

For the grating, the procedure described at https://www.domesday86.com/?page_id=2896#Grating_temporary_adjustment  can be done with this player too. The only problem is that the player spins the disc up, gives up, and spins it down again over and over when it is not happy about things. I removed the turntable motor connector, but connected the tacho wires from the motor to the power board using jumper wires. This allowed me to power the dc motor externally. Doing this (I started low but think about 5V was sufficient), the player detects that the disc is spinning and turns on focusing (triggered by the rotational speed of the disc). So, with focus, but mirror servos still disconnected, measuring the radial signal looks very much like the signal for the Pioneer LD-4300D (see link). So, turning the adjustment clockwise, it is easy to find the "on track" signal (where the tangential error is small despite tangential tracking being off), and then to adjust to make the signal amplitude maximal. This is more or less what the service manual does, only that it requires the player to actually play a disc.

So, any ideas when it comes to coarse adjustment of the quarter-wavelength plate?

I assume the procedure in the service manual is correct, but it would be good to find a way to make a coarse adjustment. It turns out that bigger adjustments affect the diode adjustment, so I'm assuming the adjustment in the manual is really fine adjustment only, or it would have to be before the diode adjustment, or at least mention that it needs repeating. The adjustment is rotational, which is logical since we want the beam to hit the wave-plate so that the angle between its fast axis and the light polarization axis is 45 degrees (to make the light circularly polarized, as opposed to elliptically polarized). I do not understand if the polarization state is really important when the light hits the disc, or if the only important thing is that the beam will be linearly polarized again, when it passes though another time. Anyway, if the angle is not 45 degrees, the beam will not have perpendicular polarization after passing it a second time, so the Wollaston prism will not divert all the beam back. I can understand this is important, but how can it have the effect described in the manual?: "Incorrect adjustment of the quarter wavelength plate makes the objective rather noisy". Just using the same procedure as in the coarse grating adjustment does alter the noise of the focusing, but not in a way that can determine a globlal minimum... (the range to try is limited since after a while the laser loses focus, due to the diode getting out of alignment)

Any ideas or insights welcome! 🙂

Staffan

So, adjusting the quarter-wave plate was problematic (the player loses focus if adjusting too much, since it seems the light path is changed a bit and the diode array needs re-adjustment). As I said, the player was constantly skipping forward with the best adjustment I had. What I did was to remove power to the slide drive. The player then just plays a few frames over and over. This was enough to check the amplitude of the video signal from the pre-amp, and at least checking what direction of the quarter-wave plate adjustment made it higher. So I did this, re-adjusting the diodes as soon as the player lost focus. After a few cycles things are much better.

I still have problems starting playback: I have to fast-forward a bit for the player to start playing. But after that I get what I would describe as better than expected color video on my monitor:)  The player plays fine for over 10 minutes with no skipping whatsoever! There is video noise, but not much at all. After getting halfway through the disk something bad happens and the player starts losing vertical sync. I will go through all the adjustments again just to make sure everything is as good as I can make it, but there could be something else going on. This is a CLV disc (the only PAL disc I have), and there are some contacts that tell the player the approximate location of the pickup, which is used in the motor drive to help set the turntable speed.

Not that it actually affected troubleshooting much, but the b/w picture was not related to the player at all: it was a bad trim cap in my monitor that made it not display color at all for PAL signals. (NTSC was working fine, since it uses separate oscillators depending on the input signal.) I thought I fixed this very problem before but apparently not...  I might start another thread for help with that.

As for the audio being only noise: I didn't know this, but PAL laserdiscs had either an analog audio track or a digital audio track, and they use the same spectrum in the RF signal. So, this really old player just doesn't know about the digital track and just plays it as analog audio. So, there is hope that audio is actually working!  Time to shop for Laserdiscs -- this time with analog audio.

Staffan

@staffanu

"PAL laserdiscs had either an analog audio track or a digital audio track,"

This was the reason that NTSC discs were more popular in the UK since there was room for both analog and digital tracks, the extra tracks were used for directors commentary or dts encoded 5.1 surround sound, PAL laserdiscs were a bit of a scarcity in the mid/late 1990s which was the peak of this format, although sales were never very high. I remember Tower records in London had a large laserdisc selection, but I bought most of the ones I own by mail-order from a French company or in the US.

@mfd70

Right -- I only have have NTSC discs too (I'm in Sweden so also PAL country), except for the one I got to try out the VLP600 player. Mostly because that is what's available. I didn't know about the audio difference at all.

I'm not imagining getting myself a PAL laserdisc collection, but the nice thing with these compared to newer LD players (except of course being in generally worse condition and being PAL only 🙂 ) is that the physical size of the optical path is large, so it is actually possible to tinker with its components. I've learnt a lot about optics in the past few months... When its fully working I have no idea what to do with the player(s)...

Staffan

Staffanu,

Do you have any updates on the repair of the Philips VLP600 Laservision player?

Being a long-time collector of Laserdisc and Laservision myself, I own the historic VLP600 and VLP830, VLP835
players too.

I would like to repair these players, but I find things very complex. And haven't yet started any repair attempts.

Crusty seems to have a lot of knowledge, giving the extensive details about repair attempts in the old tread:> https://www.radios-tv.co.uk/community/vintage-vtr/1982-philips-laservision-vlp-600/

But this tread is closed. So I cannot reply, and ask Crusty to connect.

Any chance we could contact Crusty?

Maybe I can add some information that could help. A dutch friend of mine has digitized old Philips Professional Laservision Service discs that show detailed instructions on repairing the VLP830 and VLP835:

I wonder if similar discs have been made for the VLP600?

About Laserdisc repairs... I live in Belgium, and know that some people at the "Philips Historische Producten" Museum in Eindhoven, the Netherlands, attempt to repair the old VLP players. I will try to contact them again, and see if there are any updates...

Next, I also know a guy in Germany who has repaired dozens of modern Pioneer Laserdisc players. I plan to reconnect with him, and ask him about his expertise in Laservision repairs.

We should try to synthesis all this information into one big "Laservision Repair Course".

Crusty, when you are reading this post, could you please connect with me?

Regards,

Christian