DiscoVision PR-7820

[MIPS]

After about two months of work and planning this thing landed on a workbench late last night. I'm gonna take a hit on this but I'm declaring it the first laser videodisc player to reach mass production, beating the VH-8000 almost exclusively by its internal use for quality control.

I'm working on pictures right now but immediately I'm running into three major issues. While it does turn on and suck a spinning disc under the fixed laser:

-The laser interlock is sticking. There is grease or a perished rubber bumper somewhere beneath the laser assembly that prevents the disc from automatically opening the path for the laser
-It's struggling to focus/find a sync signal off the disc. I can hear the focus servo run a few times before the player gives up. I can see some of the optics are fogged but cannot tell if this is front or rear coated mirrors which complicates cleaning them without scratching them
-There is an o-ring on the spindle lock that has perished. When a disc was loaded and clamped it immediately proceeded to glue itself to the disc hub.

[Ed in Tx]

Sounds like a real project. Good luck! If I ever find the training materials I still have (but are buried) you're welcome to 'em.

Meanwhile print out your own training certificate I've attached and wave it over the unit like a magic wand. About how much that certificate is good for!

[MIPS]

Heh, I'm going to have to figure out a way to upscale it to the size of a page but that will look great on the wall!

Anyways I had to get it home to do more work on it, plus photos, so here are some of the cleanest photos you'll probably find on the internet.








This particular unit was manufactured in February 1980, four months before Pioneer would release the VP-1000 and likely not long before PR-7820's stopped selling under the DiscoVision brand and instead under the Pioneer PR7820 Model I/II/III name. I do not unfortunately have the remote.

I cannot really proceed much further until the rubber hub bumper is replaced. A suggested replacement was part of a bicycle inner tube as opposed to an O-ring. I need to dig through the service manual (I found the FULL thing, it's 135mb!) on how to remove the spindle for cleaning but I cannot proceed to the laser issues until then.




Like I mentioned with my initial check the laser is good. The mirrors were oh-so carefully cleaned but with a disc loaded the focus assembly drops down and then snaps back up to try again. It does it as well with a disc not loaded (the machine lacks a disc presence sensor so you can operate the unit without a disc installed) but is a lot gentler with the focus attempt, so it does know SOMETHING is spinning but I can't tell if it's because of a pickup issue or the molten bumper causing the disc to wobble too much to permit tracking.
The laser is also delightfully dangerous.



The only other thing I still need to research is that there is a battery in the unit! It's behind a panel underneath at the lowest point of the machine where a leak is acceptable and it's easy to clip the leads and remove. I have no idea whit it might be for aside from keeping the 1K dump memory alive for short periods of time.

[Ed in Tx]

I tried uploading the big version 200+ KB but the web site scales it down in size to under 122 KB. Maybe I can save it to a PDF later.

After seeing that melted down rubber goo on the spindle, I wonder about the material used for the mirror suspension.


Here ya go... ☺

[MIPS]

Hehehe, pardon me as I run off to the print shop.

So that I can tell so far, I've already screwed up, ironically.
I was able to clean the rubber off by removing the screw on the top of the spindle and disassembling the latch but when it came to the sticking laser stop I had to get underneath the optical deck as up to now I was just pushing it open with my finger when the disc moved into place. The deck is mounted with three posts and three hex nuts. As it turns out if I had read the manual this step requires realignment once the deck has been moved, so sure the stop moves freely now but without the specialty jigs I have no way to realign the deck. Mother$*&@.

Also as it turns out there's a Ni-Cd battery mounted underneath the machine in the lowest possible place. Apparently the 1Kb of dump memory (the player can operate as a standalone device for interactive discs by data being stored in audio format at the the beginning of a disc in the Right channel) has a battery backup for power interruptions. Why it has this exactly I can't figure out as after a power failure you will need to restart the disc again anyways which would automatically reload the dump. Anyways a battery of this age is obviously going to be leaking and it's pretty easy to clip out.



Edited: Oh but this is kinda cool. While this is all the original DiscoVision livery, the internals have been upgraded to the Pioneer PR7820 Series III, which was the late revision just before it was discontinued. The two big things here is faster access times and complete support for all the available interactive DiscoVision titles, plus backwards compatibility with the older host interfaces.




One of the things included with the player was a print copy of the programming reference for the Series 3 revision. I have yet to find it online anywhere so I'm rather desperately trying to find a place to get it turned into a PDF.

[MIPS]

Originally Posted by Ed in Tx

After seeing that melted down rubber goo on the spindle, I wonder about the material used for the mirror suspension.

I spent a few days looking over the optics and reading the manual and that I've been able to tell without having to remove set screws and aligned parts there is no rubber used in the entire laser platform. Tangental tracking and focusing is performed using permanent magnets and coils.




I'm currently experimenting with various sized inner tubes to replace the rubber sleeve. So originally it was a rubber cup that's exactly the diameter of the hub ring on a laserdisc and the spindle. The spindle latch is a tapered assembly that under spring load is extended. When you press down to lock the disc the tapered portion pushes the sleeve of the cup outwards and uniformly holds the disc by the hub. Right now I have a bicycle inner tube that is a close fit but a millimeter or so too wide, so I have to hunt down another one to see if I can get a better fit. If it's too loose it overhangs the spindle and the disc won't fit.

This is the assembly disassembled, plus the manual diagram.




This is the cup itself. MCA and Pioneer list the part number VXX-003 "Rubber Plate Assembly". Pioneer's parts department still lists it as existing and costs $51.20 however as of this post the page indicates it is no longer available. - http://parts.pioneerelectronics.com/...tNum=VXX%2D003




Note the yellow material is the original adhesive that was used to bond the rubber to the disc.

[Ed in Tx]

I was thinking there is some sort of polymer or other material holding the mirror-coil to the magnet, but it's been 40 years since I dissected one.

Did you get it to play yet?

[MIPS]

It's still doing the same thing. I have not attached a scope to it yet or any multimeter as all the major boards are underneath the spinning disc and service jigs are needed to break the wiring out. I want to be sure the disc won't spin off or scuff before I start hanging wires off it.

[MIPS]

I've had no luck so far still trying to figure out a replacement piece of rubber.
Meanwhile I have scanned in the programming reference I received with the player for the Model Three upgrade. There appears to not be another copy available online digitally, just for the Model Two, so this should be helpful to a few people. Please note that while I removed the original staples and the pages were still tight, pages 89 to 101 are missing.

https://www.dropbox.com/s/sjexocs6al...duced.pdf?dl=0

Edited: Actually, if anyone wants to look at ANY of the available service documentation I have on hand, I just uploaded it all to archive.org. It should come up in the texts section of you search "Discovision".

[MadMan]

For the rubber cup, push comes to shove, you might be able to have a machinist turn a piece of rubber down. It'd probably have to be a rubber puck put into a hole in something solid and the entire inside get cut out. It'd have to be frozen, too, but I think it's still possible. Easier than that, you might try making a mold and using silicone. The mold would be very easy to make, you'd only need a cup with the inner diameter of the outer dia. of the part, and another with the outer dia. matching the inner dia.

[MIPS]

BuMPing this because two months ago I was moving things and oh crap, I forgot I still had this! >_>

So testing found the voltage rails were stable, the photodiode was detecting "something" and when I poked at all the capacitors I could reach with a Capacitor Wizard they were mostly reading fair but many of them are bipolars so I don't immediately have replacements readily available.
I made the bike inner tube behave and with no less than two different remote controls I can now say the player is completely functional, except for it still will not lock onto a disc and display anything. There is a test point for indicating a focus error condition and that doesn't seem to be indicating a problem.
At this point I have not seen another 7820 to compare with or buy that was less than $400usd, which is crazy money for untested equipment and these are not the kind of things you want shipped through USPS these days because they are so incredibly heavy. The best I can offer to anyone is all the service documentation is still up on Archive.org and I can break down what my problem is into a video - https://www.youtube.com/watch?v=DHCD0MMAPUM - but otherwise I'm in serious need of help because I'm stumped. I have been told twice now from the arcade people that the power is a must-do for recapping but when asked "how" they won't answer. They didn't even dodge the question. They just dropped the advice and never replied agian. All PSU wiring is stake wrapped and soldered and going back to the beginning the PSU lives beneath the optical deck, so somehow they were pulling that off and reinstalling it and then being able to align it but again.

[ChrisW6ATV]

Originally Posted by MIPS

The deck is mounted with three posts and three hex nuts. As it turns out if I had read the manual this step requires realignment once the deck has been moved, so sure the stop moves freely now but without the specialty jigs I have no way to realign the deck.

In early 1984, I bought a Pioneer VP-1000 for $50 that had a broken gear in the optical "sled" drive assembly. Once I replaced that, the player worked well except that it had a pretty bad crosstalk problem with Extended Play discs. I talked to the Pioneer service department, and they said it likely needed the "spindle height adjustment" done to fix that problem, but the jig to do that task was a $75 item. $75 then was like $500 to me now, so I never did get it fixed.


I do hope you have success in getting this player to work. In my pile of things to do when I retire is a Magnavision VH-8000 player that also does not recognize/read discs, if I remember right. These early machines have a "cool factor" that makes them much more interesting than all of the look-alike front-load black players from 1985 and later.

[MIPS]

I have at least three VP-1000's now as after one appeared people started just sending them towards me. One turned out to be a pre-recall unit (overheating issues) which means it's a really early unit that never saw a service center and they all seemed to work after a heavy cleaning (one in particular had a dirty encoder on the sled so it didn't know where it was until that was cleaned). They use the same Toshiba tube as the 7820 as well so unless the 7820 previously had an insane amount of hours I'm not considering the possibility I'm looking at wavelength drift from age or helium diffusion which will affect the playback.
I've considered getting a magnavision as they seem to show up from time to time but for being the loser in the first generation players it's also the most expensive. It's arguably "the first*", it looks way cooler than the 7820 and it had that Leonard Nimoy celebrity endorsement.

[Hawkwind]

"it looks way cooler than the 7820 and it had that Leonard Nimoy celebrity endorsement."

I believe he also endorsed Betamax too, back then. Are you familiar with the web site Laserdisc Database?

www.LDDb.com

I'm a member there, and they would love to see/read about your PR-7820. If you want another pre-1985 player look for an LD-660 or a PR-8210. Don't waste your time/money on a Magnavox player unless it's for display only...