Video heads in a Super VHS-C Camcorder - Page 1
Forum section: electronics / repair

author: steve30
author_rank: Frequent Contributor
timestamp: August 29, 2019, 04:00:17 pm
content: I got a couple of mid-1990s Panasonic S-VHS-C camcorders off ebay recently (models NV-S85B and NV-S70). They "work", but the heads don't spin smoothly, and they make a lot of noise.To demonstrate this I made a video on my YouTube channel, showing the camcorders "working", and also did a teardown of one of the heads. I've never dismantled a video head before so this was quite fascinating to see.The problem clearly seems to be friction in the spinning transformer part of the head.Does anyone know if it is possible to repair this problem or not? I'd welcome any suggestions.Thankssteve30YouTube video:

author: Renate
author_rank: Super Contributor
timestamp: August 29, 2019, 08:09:38 pm
content: I've never tried to fix one of those transformers, the tolerances must be tight and it might have eaten the windings.When you put the drum back on, you'll have to set it for eccentricity.You use a gauge and rotate the drum by hand.With screws slightly tightened, tap it with a screwdriver handle lightly until it's there.But you know all this already?And dihedral, too. (But I'm nit-picking.)

author: coromonadalix
author_rank: Super Contributor
timestamp: August 29, 2019, 08:23:32 pm
content: the noise mostly come from the head base bearings, normally you change the complete base assembly, and you have to remove the head, and you have to redo all @renate wrote previously.If you want to do lot of work, you have to find the exact bearings specs, use a puller .... you know the rest.

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 30, 2019, 12:13:26 am
content: +1 on the bearings...To encourage you a little: I once replaced 2 worn (they wear eventually giving poor frequency response) heads on a VHS drum without any specific equipment.That was a whole lot of fun and VHS is more to human scale than your camcorder.If you do disassemble and your drum has an opto or hall angular position sensor (motor side) make sure you can get that realigned with the drum accurately when you do reassemble.

author: Rasz
author_rank: Super Contributor
timestamp: August 30, 2019, 07:18:16 pm
content: unmistakable sound of bad bearing, old worn cpu fans sound the samesquirt some motor oil for a quick *short lived* fix

author: steve30
author_rank: Frequent Contributor
timestamp: August 30, 2019, 11:17:29 pm
content: Thanks for the replies.Is a squirt of lubrication likely to be worth trying? If so, what kind of lubricant should I try?Bearing in mind that these are obviously knackered already and there is nothing to lose by trying anything.

author: Rasz
author_rank: Super Contributor
timestamp: August 30, 2019, 11:42:31 pm
content: I use whatever is inside a 50ml bottle of "special lubricating oil for paper shredders" I got around 2000, one application on bad bearing cpu/gpu fan used to revive them for up to a couple of months

author: amyk
author_rank: Super Contributor
timestamp: August 31, 2019, 12:37:22 am
content: That was extremely painful to watch.The sound is characteristic of a dry sleeve bearing. Did you try spinning it without taking the drum apart first? In your video you show the drum coasting to a stop and it doesn't "stick" in the way that it would if the rotary transformer was rubbing. The fact that it "spins freely" without the rotary part of the transformer attached means nothing, because sleeve bearings can feel perfectly smooth yet start chattering when they reach operating speed without lubrication. The rotary transformer is NOT a bearing and the air gap between the two parts isextremelysmall. Had you not separated the rotating part from the drum, you may have stood a better chance of getting it working again once the bearing was sufficiently lubricated.Quote from: Renate on August 29, 2019, 08:09:38 pmNot in this design --- the bearing is part of the drum itself. But he will need a dial indicator to get the rotating half back on the drum, true enough to not rub.If the bearing has worn enough that the play increases to the point that the rotating transformer begins to rub (again, even a dial indicator would've saved you the trouble here...), it's probably not serviceable. Maybe aslightlythicker oil might help keep it centered, but the prognosis is grim.

author: steve30
author_rank: Frequent Contributor
timestamp: August 31, 2019, 02:08:01 am
content: Interesting phenomenon... I've just been playing with the parts of that dismantled head, and I managed to put it back together, and now it seems to spin nice and freely. I'll see if I can put it back and make it work somehow but I've a feeling I may have damaged it, so I'm not holding my hopes up.I've now decided that the rotary transformerdoesspin freely, contrary to what I showed in the video. I removed the motor, and put the transformer in, and it spun fine. So the friction is somewhere either in the motor, or between the motor and the transformer.amyk: Yes, I spun it without taking it apart. It spun 'kinda' freely. It wasn't smooth all the way round.

author: amyk
author_rank: Super Contributor
timestamp: August 31, 2019, 02:30:09 am
content: The tolerances are tight enough that the slightest bit of oil residue or other contaminant in the bearing/air-gap will cause drag.Quote from: steve30 on August 31, 2019, 02:08:01 amEspecially given what you did with the heads, it'll be a great miracle if they even work at all. Be sure to clean the drum surface with isopropanol (and let it dry) before letting it contact any tape, making sure to remove any dirt from the air-bearing grooves, or you'll destroy the tape too.

author: Qmavam
author_rank: Regular Contributor
timestamp: September 01, 2019, 02:07:19 am
content: I have one experience in the late 80s, taking one of those apart. I repaired an open wire in the rotory transformer.Unfortunately I put something back together with the wrong orientation so while it worked the pictured had somesensor timing distortion. Actually took it with me to a Philips VCR training class and ask the instructor, he new just what to do.Now, you seem to already have found the problem with just trying to spin the transformer winding. It needs to be connected to the head ass'ywhich is connected to the bearing giving it support and centering it. So, ya you can't just spin that plastic piece with the winding without the head ass'y.If that tape had video on it than there is clearly a head problem, could be dirty or broken. But, I'm not a 100% convinced the noise is from the video head bearings.Can you isolate the noise with a tube, straw or stethoscope? Could it be a the capstan motor or one of those automatic head cleaner things that is not moving awaywhen it is supposed to? Or, less likely, something in the reel drive ass'y?Is there any way to get the head motor ass'y to run outside of the unit, to either verify it as the source of the noise or rule it out?Good Luck, Mikek

author: steve30
author_rank: Frequent Contributor
timestamp: September 02, 2019, 04:58:47 am
content: Quote from: Qmavam on September 01, 2019, 02:07:19 amHow did you go about repairing the wire in the transformer?I can confirm that the noise is definitely coming from the head drum. Its not as obvious on the video, but it is obvious in real life.I'm pleased to report some success. I wassometimesgetting a bit of resistance in the head bearing while spinning it manually, so today I put a little dab of oil in the bearing, and that has smoothed it nicely. I reinstalled the head and reassembled the camcorder and I'm pleased to say it more-or-less works and is very quiet.Unfortunately I managed to break off one of the head chips from the drum, and it clearly needs some alignment. I am also getting a periodic, quiet, high pitched sound which I think is coming from the head.Nonetheless, it works a damn sight better than it did when I got it.

author: TurboTom
author_rank: Super Contributor
timestamp: September 02, 2019, 08:18:14 pm
content: I'm quite doubtful that it's the drum or its bearings. Usually, the drum suspension incorporates two preloaded ball bearings of very high precision. They won't produce the noise that's audible in your clip. When worn, they rather sound like an ancient hard drive.The noise appears to originate from dry or worn sleeve bearings (as others have pointed out) where the shaft "dances" around instead of rotating around its center. There may be several places where sleeve bearings are used in a camcorder drive mechanism, one that's rotating considerably fast is the capstan. In a machine of that age, I'ld also expect the rubber capstan roller to be far beyond servicable condition. Then there is the reel drive mechanism that may produce similar noises. This is either driven by its own BLDC motor or via an accessory drive by the capstan motor.These mechanisms, even in their day, were considered hardly repairable, since their alignment is super-critical. I remember having tinkered with many Exabyte Video8 streamers and later on those DAT streamers (since I got them virtually free of charge) during my university time, trying to make a good one out of two or three "corpses", with very limited success. Working on S-VHS-C machines shouldn't be much different except that you may actually "see" the results of your action.Anyway, these mechanisms are some intriguing engineering pieces and for sure are enjoyable for someone with "watchmakers" skills and interests...Cheers, good luck and have fun with your "prey"

author: Qmavam
author_rank: Regular Contributor
timestamp: September 03, 2019, 04:10:35 am
content: Quote from: steve30 on September 02, 2019, 04:58:47 amI don't remember the exact procedure, but I ended up with the unit, sometimes I bought them if the declined repair,sometimes they just never picked them up.But anyway the transformer was open, a visual inspection showed a clear brake of the wire inside in the actual track in the ferrite.I somehow got the wire varnish cleaned off enough to get it soldered, and covered it with a thin coat of epoxy. That solved the problem,and got video back, but I had something assembled wrong so the phase was incorrect and the picture was weird, I can't remember exactly, but thesync signals were in the middle of the picture or some improper thing. Like I said I told the factory rep what I had done and he looked at thepicture and knew exactly what was wrong.QuoteMaybe now that it has some oil, running it a bit will help make it better.If you broke the head, I think you will just need to replace the whole head ass'y.I remember breaking one on a Hitachi, luckily a little paperwork finagling and the factory paid for it under warranty.The statute of limitations has long passed!Mikek

author: steve30
author_rank: Frequent Contributor
timestamp: September 03, 2019, 05:18:37 am
content: Qmavam:Sounds like you did a good job with the rotary transformer repair, even if it didn't work properly. I now have another similar camcorder with the same problem. That one will just get a slight lubricating without having the extreme teardown that this one had.For those interested, here is a close up of the broken head:Here is the kind of image it is now playing and recording. There is a noise bar at the bottom of the screen and the image jumps around a lot. This was the best I could get it after fiddling with the tape path adjustments.For those interested, here is the head with the very top piece removed revealing the shaft which got a little bit of oil.Here's the bit which screws onto the very top of the head. Not sure what you'd call it, but it has a nice pattern on the underside.

author: TurboTom
author_rank: Super Contributor
timestamp: September 03, 2019, 07:29:47 am
content: Very interesting! So I stay corrected - that's the first time I've seen (photos of) a helical scan head with hydrodynamic bearings like they are used in modern hard drives. The spiral grooves of the axial bearing plate will force the lubricant to the center when the drum is spinning in the correct direction, resulting in a very well defined "oil cushion" there. Without the oil, it obviously won't work as intended. Usually, the lubricants for these applications are rather special (viscosity-, adhesion- and surface tension-wise).Cheers,Thomas

author: steve30
author_rank: Frequent Contributor
timestamp: September 03, 2019, 10:10:38 am
content: Thomas: I was kind of expecting a ball bearing when I took it apart. I gather many video heads do use ball bearings. I wonder if they went for the sleeve bearing in this one because its Compact VHS and so needs to be smaller.I've just had the other camcorder apart (the model S70) which exhibits the same symptom. I just put a drop of oil on the top of the bearing and now it works perfectly, so it looks like that was all that was needed.I was a bit concerned about exactly what viscosity of oil would be suitable for such an application. As I don't have much selection of oils here, and as these are pretty much scrap anyway, I used bicycle chain oil.I'm just wondering if I will be able to swap the S75's head into the S80, since the S85 is a better spec camera. The heads (and the rest of the mechanism) look the same so I'm guessing I can. Only one way to find out I suppose.

author: amyk
author_rank: Super Contributor
timestamp: September 03, 2019, 11:43:05 am
content: Very light oil is all that's required, given how fast these spin and how little power they draw.I wouldn't be surprised if the head drum assembly is the same--- here's a (very long) video of a head swap between a camcorder and a non-camcorder:Just remember how fragile the heads are and be careful handling the drum assembly, it should be OK.

author: Qmavam
author_rank: Regular Contributor
timestamp: September 04, 2019, 01:29:18 am
content: Steve30,If that is your playback, I think you can solve at least the playback without a new head. First I would make sure that damaged head is not sticking out or moving out* when it spins and scratching the tape.Next I would check how the tape flows around the complete drum ass'y, there is a guide at the bottom that it just barely slides along, you are either to high or to low on one side or the other. The guides that pull the tape out and around the head are adjustable, I suggest one of them needs adjustment, In fact you can probably use a finger and move the guides up or down while watching the picture and figure out which one you need to adjust. You might need to cut a slot in the middle of the blade of a flat screw drive to make that adjustment.Now, I don't know what the broken head is. Is it hifi audio? Is it a flying erase head. Is it a slow motion head. I don't know, I do know if it was one of the two video playback heads, the picture would look different. Every other line would be snowy, not just the lower 20%.I think that it a tape path adjustment problem.*Or even shifting the tape and causing that 20% that is snowy.

author: Qmavam
author_rank: Regular Contributor
timestamp: September 04, 2019, 01:38:32 am
content: I looked at the youtube and clipped a picture.I show the guide and point out the tape must be just right in the guide.I think you might be able to see at one end or the other it is high or low.Pull up or push down while watching the picture, I think you will see the picture clear up.

author: steve30
author_rank: Frequent Contributor
timestamp: September 04, 2019, 05:46:21 am
content: I'm not sure what that broken head was. I don't think its the flying erase head. It *could* be a video head, since the video is problematic, or it *could* be a HiFi audio head since it wouldn't record/play HiFi. I don't know. Either way, I couldn't adjust the tape path to get any better than what was shown.However, I did transplant the newly repaired head from the S70 into the S85, and it is now working nicely. Not perfect, There's a little bit of noise at the bottom of the picture, or if you adjust it so that is good, the HiFi audio goes noisy. But I'd say its about as good as I can expect from a knackered repaired 22 year old camcorder.Now to make a new battery pack. Fortunately these old machines use a bog standard arrangement of 4 NiCd cells in series with a temperature sensor. I reckon some AA Eneloops and a bit of electrical tape will suffice.

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 04, 2019, 07:48:20 pm
content: Does it have a static head anywhere? (Erase + tracking)That could be misaligned.

author: iRepairElectronics
author_rank: Contributor
timestamp: September 05, 2019, 06:53:28 pm
content: once you break one of those heads, your screwed. there is no replacing one of those.i used to work for the a company in the US that imported replacement video heads. no one makes them anymore.best you can do is get on old one for parts and hope the heads are in good shapethe alignment is done at the factory then the red glue is added aft wards to the set screws.what was pictured is what we used to call a double twin. 2 heads mounted on the same piece, then there is a companion 180 degrees opposite to it.one is likely for SP and other for EP/LP.