CED VideoDisc and Player Discussion

[CEDken]

I have an SGT-250 recently acquired. It is clean inside and doesn't appear to have had anyone poking around. When a disc is inserted the stylus arm rapid travels toward the center of the disc and holds there. Pause, power and unload buttons all function. This is the first time I've worked on a "G" player. Any help?

[CEDatum]

The most likely cause for arm travel is a stylus cartridge with a weak fly lead. A weak fly lead cannot apply enough pressure on the stylus diamond tip to pick up a continious signal from the disc surface as it rotates. And the player 'thinks' it is seeing a 'drop out' from a damaged disc. So it nudges the stylus tip to the next groove. This is a quick and continious process and the stylus arm moves to the inside of the player. Sorry for the sermon !

So replace this stylus with a known good one.

Other, but less likely causes are:

Problems with the stylus arm servo or the turntable height on the player is set too low.

Amanda at CEDatum cedatum@ccrtc.com

[CEDken]

Yes, the new stylus cured that problem, thank you. It plays now, sort of. I think that the electronics troubleshooting it needs is beyond my skill level. Time to either shelve it or send it out for repair.

[RT9342]

I recently bought an SGT-250 as well. There's something strange about mine - maybe someone can give me some insight. Those of you who are familiar with the SFT and SGT models know that the tonearm has a copper cover plate soldered on. In my player, it is black from oxidation. Black as charcoal on the outside. Inside (under the stylus cover), it's not blackened, but it looks almost as if it is burned. And the fly lead on the stylus is totally black. But here's the weird part - everything else (non-copper) looks almost as if it's brand new. The solder joints appear to be original, so I don't think it's ever been rebuilt or anything. It does smell like it came from a smoker's house though. Would the cigarette smoke do it? My grandfather used to smoke a lot, and his SFT-100 did have bad looking copper parts, but they were not black, and most of the metal parts and all of the labels showed signs of nicotine stains.
I didn't expect the stylus to work at all, but it plays. However, when it first starts up, it stays at the beginning, like if it's in page-mode or something. Fast-forward fixes that, but every once in a while (after 15 seconds or so, or even a minute), the picture gets snowy for a second, then the player sort of randomly skips around the disc for less than a second and then goes back to where it was. Perhaps due to the oxidized fly lead? I just hope it's not a bad tonearm. I do have a couple of spare tonearms, but I'd rather try a replacement stylus before replacing the whole tonearm.

[RT9342]

Well, I finally got my SGT-250 fixed. I'm curious as to how CEDken's SGT-250 is working, and if it might be having any of the problems I encountered.

I suspected that I had a bad stylus. John from CEDatum agreed, especially when I told him about the blackened flylead. But I discovered something strange with the servo motor while trying to diagnose another problem.

I noticed that it was pretty difficult to remove the caddy after loading a disc...but the caddy would come out easily when removing a disc. If anyone with an SFT-250 has experienced this problem, here's what I found the problem to be: there's a switch in the front left corner of the player that senses whether a caddy is inserted or not (all of the other SFT and SGT type players do not have this switch). If it's even just a little out of alignment, the caddy won't activate the switch, so the player thinks you already removed the caddy and tries to raise the turntable to playback position while the caddy is still in the player. The friction between the turntable and the caddy is what made the caddy so hard to remove.

After fixing that problem, I watched just to make sure all was good and then discovered that upon startup, the servo motor would drive the tonearm to the starting position and would then just shut off completely. But about every 15 seconds, the picture would get snowy, and then the servo motor would ram the tonearm forward, causing the movie to skip. This is how the player continued to play the disc. Also, the servo motor remained at a standstill during visual search forward; only reverse or any of the rapid access functions would operate the servo motor. I tried to adjust the servo balance adjustment in the tonearm, and it made no difference whatsoever. That's when I suspected that there was either a problem in the tonearm or the computer, not the stylus. I replaced the tonearm with the one from my old VP-2000 that I parted out (in case anyone else tries this, you need to use your SGT-250 stylus cover from the old tonearm - the black plastic latch on the older tonearms sits too high to clear the stylus access cover on the SGT-250, but the original latch from the SGT-250 is contoured differently to compensate for this). The replacement tonearm started fast-forwarding immediately upon playback, but after adjusting the servo balance adjustment, it worked flawlessly.

Anyone else ever seen a tonearm go bad? This is the first time I've ever seen it. I just wonder if it's serviceable. There seems to be nothing wrong with the resonator - it's got to be something in the servo circuits or the stylus tip sensors or something.

[CEDken]

Thanks for asking about my SGT-250 player status. It has been tagged with the status and put on the shelf for future disposition. I don't have the depth of knowledge of the electronics of an SGT-250 to be able to diagnose it myself and spending $150 at this time to have it repaired doesn't seem a wise move. On the brighter side, I was encouraged by this incident to open up an SJT-200 that I purchased some time ago. It had the usual problems from the loader belt to some shipping damage from transport without locking tabs. It is working great now.

[RT9342]

Glad to hear you got an SJT-200 and got it to work. That's a good model; I think most people prefer the SJT/SKT models over the SFT/SGT models. They're supposed to be easier to work on. I personally have an easier time fixing the SFT/SGT models, but I think it's only because of familiarity - I've worked on those a whole lot more than the SJT/SKT models.

Before disposing of your SGT-250, I would suggest seeing if anyone might want to buy it. I would actually consider buying it myself, though I probably wouldn't be able to do it before the end of the year, do to all of this holiday stuff, etc. Though my SGT-250 works fine, I wouldn't mind having a spare, or at least spare parts.

So what exactly is still wrong with your SGT-250, anyway? I know you mentioned a tracking-related problem that you were having prior to replacing the stylus, but what about with the new stylus? Is it still having some kind of tracking problems? That unfortunately seems to be a common problem with the SFT/SGT models that I've come across, though it's actually pretty easy to fix. There's an adjustment in the tonearm, accessible through a hole in the metal cover on the right side of the tonearm. It's labeled "SERVO BAL. ADJ.", and the easiest way I know to adjust it (contrary to what the service data suggests) is to simply adjust the control until the tonearm drive gears appear to move the seem speed in visual search forward and reverse. I've occasionally also adjusted the servo control on the microcomputer board, just to improve stability, but most of the time, that wasn't necessary. That's if nothing's actually burned out. In my recently acquired SGT-250, the controls made no difference, so I knew something was wrong, and replacing the tonearm fixed it.

[CEDken]

The picture is dark and there is no sound. I certainly could try that adjustment to see if it makes a difference siince it still doesn't track very well.
I wouldn't discard this machine and I have a few others that also have various problems that are awaiting the time to evaluate and repair. The mechanical repairs are usually pretty enjoyable but when it comes to electronic problems, although I do have some training in electronics, they are a little advanced for me. Sure, I can track it down to a group of components that may be causing the problem and start replacing, but then there is that time issue.

I must agree that I do like working on the SJT models much more than the older ones.

Ken

[RT9342]

Dark picture & no sound? There's a new one for me. I've seen VCR's with dark picture and/or no sound - usually in a VCR, the dark picture was the result of low RF signal, but I don't know if that would have the same effect on a CED. A weak RF signal could indicate a problem with the tonearm, but I'm wondering if the signal board in the player has some serious problems. To be honest, when there's major signal problems in one of these machines, that's when I usually end up parting out the machine and getting a new one. For the most part, I don't mind working on the older chassis (and with your comment & other people's comments, I'm feeling more and more that I'm the only person in the world who doesn't mind working on the older chassis), but I agree that some of it (especially the signal circuitry, which unfortunately is almost the same in all CED player models) is quite complicated.