Hello-

I am working on a 1977 Sony Betamax VCR, model SL-8200. This is the first Beta with two speeds (BI or X1 and BII or X2). I have replaced all of the rubber components and fixed a frozen capstan motor, and now it has only one remaining problem, but it is a good one. The VCR records in both BI and BII speeds fine, and plays in BI fine, but has a problem playing in BII. The capstan motor will repeatedly rev up and down or "hunt" when trying to play any BII recording, whether done on this machine or others. Every once in a while, it will sync up and play a BII recording OK, and if left alone then it would probably play to the end of the tape, but if paused or stopped the problem returns. I found and replaced one tantalum capacitor in the servo circuits, and tested all of the other tantalum and regular electrolytic caps on those two boards but did not find any obvious bad ones. Anyone here have any tips for this problem? Thanks.

Moderators, if a VCR is off-topic (or too new) for this forum, please let me know. Thanks.

Since this was one of the first VCR's and is 35 years old, I see no problem in discussing it here.

I attended the Sony Betamax school for one week at Zenith headquarters in Chicago back in the mid-70's. At the time, Zenith was supporting the Beta format and in fact the Zenith VCR's were rebranded Sony units. Unfortunately I probably no longer have any of the training materials that went into great detail about how each section of the machine functioned.

I don't remember any discussion about failure to come up to speed only on the faster playback, and that wasn't a common problem seen during the few years those machines were in use back in those days.

Do you have a Sony service manual showing the various waveforms in the servo control circuit? That would be a place to start, comparing them between the two speeds to see what is lacking when it tries to play back a tape recorded at the faster speed.

I have that model and the Sony service manual. There are adjustments for that. The adjustment procedure has you set it up in record using a scope. I think that you could also do the adjustments in play back using properly recorded tapes and viewing the picture to know when it has locked up. The procedure is on page 6-18 of the service manual. In a moment I will type in part of that procedure in case that it will be enough to get you going.

You may have a misadjusted or worn CTL head, or a tape path alignment problem. Tape tension is also very important. The tape guides can be worn or binding, or out of proper position. Take up tension or back tension errors can cause big problems.

Lets see it this produces readable results.







Note that step 6 is fine tuning step 4. There are other adjustments in this area. I picked the ones that I think are most likely the ones you need. You might be able to just fiddle with those pots until it locks and then set them in the middle of the range where it locks. Mark their original position first.

I STRONGLY suggest that you do not just fiddle with those controls. You are much more likely to have a mechanical problem with the deck, that is, something is worn or binding or out of adjustment (not electrically).

Many of those decks cannot be adjusted properly without alignment tapes. Do the obvious first, like removing spindles and tape guides and clean them, then lubricate them. Do not just start turning controls to see what happens.

There could be mechanical problems, but I have found that the electrical adjustments drift on these early Sony's. I have to re-do the electrical adjustments every few years. We are looking for a problem that only affects one of the two speeds. The hunting of the speed sounds like a drifted adjustment to me. Note that Sony's procedure says to use an ordinary tape.

Dennis-

Thank you for the suggestions. I do not have the Sony manual but rather the Photofact one. It does have some waveforms that I can check and compare as you suggested. I scoped one point and verified that it reasonably matched (and was varying as the motor ramped but stable when locked).

Johnny-

Thanks for the notes. I have done cleaning of the tape-path components, and since the BI speed has no problems at all (and BII records fine as well), I am going to concentrate on what might be different in the BII mode, at least to start.

Tom-

I am happy to hear that you have one of these, and the Sony manual as well. Your pictures are fine, and I will follow that procedure and see what I get. Luckily, the Sams manual has pictures and uses the same Sony part numbers. I have the Sony service manual for the SL-7200 (first, one-hour-only version of this machine) which has a lot of functional detail and procedures, but this servo area is one of the big differences between the two machines. Thank you for posting the pictures and your comments.

Tom-

I adjusted those two pots and verified the waveforms and voltages as shown. Unfortunately, it did not help the problem. With both pots at 5.5V in record mode, they read similarly in play in either speed. Both fluctuate a bit during play (as I would expect, as the servo circuit does its job), with BII a bit less stable than BI (again, as I would expect since the slower speeds never look as stable on-screen either). My readings of the voltage at TP605 in the BII speed were after I got the machine to play properly (which usually takes several rounds of pausing and un-pausing the tape, hoping it will sync each time); when it is not able to sync, that voltage swings wildly from near zero to over six volts (off the top of the scope screen). One more test I will do is to record a longer section of tape in BII after the adjustments and see if it plays any easier than before.

You stated previously that it will record well in BII. How do you know this?

I started to think that maybe there could be a problem with drag in the capstan system, but as it is the slower speed that is having trouble, excess drag in the capstan and motor seems an unlikely cause.

Another possible cause is a bad loop filter capacitor.

Just in case it will help, here is the first part of the adjustment procedure that I did not post. This was to be done before the part I posted. Doing this part probably means that you should redo the second part. I will post the last parts in another post.

Here are the last parts of the procedure.

Johnny-

I confirmed that by recording in the BII mode for a good period of time, then playing the recording. That recording is no easier, and no harder, to get to play than BII recordings I already had from other VCRs, and once I do get any new BII recordings to play, they are as consistent as other recordings.

Tom-

Thanks for posting the other alignment details. I will do those procedures as well. I will post an update here.

It seems to me that there is a tape path or tension problem, simply because you can make the VCR work by going from pause to play mode; doing this would have no affect on electronic adjustments.

Johnny, the only significance of going in and out of pause mode I saw is that it starts and stops the capstan servo lock process. When I move the pause lever (even partially), the "hunting" action of the capstan motor quits (and the motor goes to a fixed, somewhat higher speed). So, using that is a quicker way of giving the servo circuit(s) more chances to succeed in synchronizing, compared to hitting Stop and Play alternately repeatedly. A couple of days ago, I also had one of the two servo boards hinged open from the chassis (these machines are VERY nicely built for service access!), and that allowed me to move one of the record/play switches back and forth. That seems to have the effect of opening the servo loop as well (removing the control head's signals from the path), and indeed, the tape and the capstan motor went to a steady speed every time that switch was moved out of the Play position. That was the first test that convinced me I must have an electrical/servo problem, since nothing at all changed mechanically between the "steady" and "hunting" conditions. During that test, I looked for anything like the reel brake band or other parts moving/changing position and saw nothing. I appreciate your ideas as well.

I did not yet have a chance to do the remaining adjustments that Tom posted.

I decided to try "tweaking" the oscillator adjustment (VR601) and got a bit different behavior but not a fix, and then I decided to check the caps again (I thought I had already done so). Several of the tantalum capacitors on that board (CS) have relatively high ESR (25-40 ohms if my meter is at all accurate). The caps are all less than 1 uF values, but I have also read that tantalums (should) have much lower ESR than aluminum electrolytics, so I am going to replace them and see what happens.

Chris-
Time warp. I bought one of these used, back in '79, and it had a ton of hours on it from the original owner. It had the outboard mechanical clock/timer, too. Used it for another 10 years, for editing and cloning family films when portable cameras came around, etc. But it made every VHS machine of it's vintage look like an Etch-A-Sketch in comparison. I know, because several of my buddies wanted to show me how better their early '80's VHS machines were at the time compared to my then 5 or 6 year old machine, so a couple of them brought over their machines. Off the air, machine to machine cloning, we went through like 2 cases of beer, and a number of different comparisons. Can't remember, it was like 4 or 5 VHS machines. And none of them did prove them to really be better. Maybe a scope would have proved incrementally better frequency response on the brand new ones, but with the sources available then? Nope, looked as good, was demonstrably better than one of the brand new machines. Finally shut everybody up, no longer heard any noise about that "crazy Beta" stuff. They did grouse about how I couldn't share movies. But no one ever said anything about picture quality and Beta ever again after that face-off. Lost it in a flood while in storage, wasn't worth tearing it down and rebuilding to me at that point. That thing weighed a ton, but was beyond solidly built.

http://www.betamaxcollectors.com/sonybe ... -8200.html

Good luck with it, that really was an awesome machine.
John S.

Update:

I replaced several tantalum capacitors on both servo boards (CS and RS-L), and I did all of the adjustments Tom gave me, and they all worked as they should. But... The problem is EXACTLY as it was before. No better, and no worse. What I also just did, though, is to pick up another of these same machines from Ebay. And, if I put its CS board in the original machine, the problem mostly goes away (but not entirely; BII recordings still cause the capstan to "hunt" once or twice each time, and sometimes more).

So, I will try things like comparing scope displays in each speed as Dennis suggested. I may also try the capstan motor from the "new" machine in the first one. That motor was replaced in the second machine in 1985 according to a note inside the machine. (It also got new video heads in 1983 in another note; nice to see these newer equivalents of service tags.)

Look for dropouts at CT playback test point during these transitions. These machines are both sensitive and susceptible to minor tape path misalignments causing the tape to slew up or down on the audio/CT stack. They discern play speed from CT and a missed pulse will send the capstan servo into a tizzy. Even the factory didn't necessarily get the alignment right.

If anything, simplicity of alignment was what VHS had over Beta. I could always align a VHS in 15 minutes. A Beta could take all afternoon. It's even dependent upon pinchroller condition.

arbilab,
I tried posting that tape path alignment and tension are critical, but my advice was not welcome. I have worked on these decks when they were still new, and yes, you can spend a nice afternoon getting the adjustments right.