Quantcast JVC Super VHS camcorder, bad head? - digitalFAQ Forum
  #1  
01-21-2021, 05:24 PM
snow_sg1 snow_sg1 is offline
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Hi,

My name is Nicolas and I live in the Secam-L country

I've got a bit of an issue on a 2001 JVC S-VHS camcorder I try to fix.

If you ask why I even bother with it, just because I love to learn everything about analog video, it has a good vibes for me. I'm learning everything myself. I've been thinkering with VCR and old electronics since I was 4-5 Yo.

I bought this camcorder broken (really, cheap, 10€). I've never seen it working before. It seem kind of average as far as hours goes, but it's complete in box with manual.

There is what I call "small wear" on the upper drum as far as I can see. Don't look high hours.

Symptom :

The head drum was seized

I took everything apart to lubricate the bearings, I've never touched the head, just the upper drum. Head have been clean with paper and isopropyl alcohol as usual.

I think I've put the head back correctly but maybe not ? I had taken pictures of head placement.

Is there is any kind of mark regarding the drum motor position to heads ?

I've checked all the heads using my multimeter, all shows 0.04/0.05 Ohm. I've looked at the rotary transformer under microscope and nothing seem cut.

I've looked at the heads under the microscope, one of them look a bit strange, the wire is hanging a bit, but maybe it's not that ? Or maybe it is

Video is OK for most part but there is a noise bar at top or bottom of the picture, depending on tape and if you look on LCD or an external monitor. Most time it show video for a second and switch to black screen. I have to Pause or FF/RW manually and play again untill image is stable. I've turned the TBC OFF to see.

Images recorded on the camera exhibit the same issue.

The tape path is correctly aligned, I'm sure, turning the guides (entry) doesn't yield any differance.

Can you help please ?

I've made a short video, it's easier for you to see the issue : (don't worry about the no color part, it's a SECAM-L recorded tape and this is a PAL camcorder)

https://www.youtube.com/watch?v=Qdps...ature=youtu.be

Thanks

Last edited by snow_sg1; 01-21-2021 at 05:44 PM.
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  #2  
01-21-2021, 06:32 PM
hodgey hodgey is offline
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Does the tape guides go all the way back as they should? It looks like part of the signal is not read of the drum or something. Head switching point being off could cause such an issue, though I don't see anything in the camcorder service manuals about adjusting it. I haven't messed with the mechanics on any of the camcorders, though on full-size vcrs the head switch point can get messed up if the drum motor is put back in a different angle in relation to the rest of the drum assembly (there are magnets and sensors that tell the system chip at what point of the rotation the drum is). Maybe something ended up being rotated differently when you put it together.

The TBC in these is from what I've tested capable of inserting a vertical sync signal if one is missing, like the video stabilizer function in the JVC VCRs (but in those it can't be enabled when the TBC is active), which cause noise bar to be in different places depending on if it's on/off and display device.

Another possibility is could be the tape guides being obstructed or not moving fully into position for whatever reason. The camcorders use a smaller drum than full-size VCRs so the tape is wrapped around more of it.
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01-21-2021, 06:57 PM
snow_sg1 snow_sg1 is offline
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Wow, thanks you so much for this quick reply !

Do you have the service manual by any chance ? Maybe I can scope the switching point or the head signal ? (I've got a Rigol oscilloscope)

So, to reply :

1) Yes the tape guides seem to go all the way in, the can't be moved further.

2) This will explain it most likely, I didn't take note of the motor position, there is a blue dot on it, I tried to align it with the red dot on the top of the head, but maybe it's not this.

I'll take it all apart tomorrow and take some pictures of the heads using the microscope. Then I'll move the position of the motor, if you're right I'll see change in the picture. If nothing change, I guess, one of the head took a long vacation ? Or it doesn't seem head related at all ?

Again, thanks so much !
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  #4  
01-25-2021, 03:59 PM
snow_sg1 snow_sg1 is offline
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Thank you very much, it's working again !

The issue was just that timing between control pulse from drum motor and the head assembly. Now all frame is complete and picture is back 100%. Heads were not at fault here.

Again, thanks so much

If this can help someone else another day.
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