Distorted bottom of the image on VHS (not head switchingnoise)

[SF01]

Greetings.

I have noticed that on my most recent recordings I get distortion on the bottom of the image, separate from head switching noise, which is also way off than normal. It looks like the bottom of the image was stretched instead of properly recorded.
Previous recordings don't have it and other prerecorded tapes work fine. Though it may be worth to note that several tapes are rolling from bottom to top hen TBC is turned on, whiel the same tapes when played with TBC off and machine power cycled mostly work fine, only few have problems, like jumping image.

Is it problems with tracking, TBC, or something else?

Attached are screenshots of what's happening.

[dellsam34]

It looks like your head switch point is off, What model VCR is this? But please do check the tape if it has a physical damage on the edge, In this case probably the top edge but do check both.

Switch point can be adjusted if it has been tempered with before, I made a video on how to adjust it on a JVC machine, Video99.co.uk also made a recent video on how to adjust it on a Samsung machine. Pretty much any VCR with a head drum motor on top is adjusted the same way.

[SF01]

Thank you for the information.
My model is JVC - HM-DR10000EU
This happens in different tapes, I've recorded test patterns on several different cassettes, all have distortion at the bottom.
I've seen Colin's video, he always has great stuff.
I'll see if that changes anything, though the playback of retail and previously recorded tapes is good.

[dellsam34]

Pre-recorded tapes are made in professional machines with high tolerance of precision and regularly calibrated, then duplicated with a contact method to make identical copies, So the switching gap between head A and head B in them is very narrow and less likely to be pickup by a miss aligned VCR, Home recorded tapes with consumer VCRs is another story.

[SF01]

Yeah, the thermomagnetic duplication system, I wouldn't mind having one.
OK, now the head isn't moving at all and the VCR turns off after inserting the tape and failing to initialise the drum spinning.

[dellsam34]

What did you do?

[SF01]

Same as on the video, loosened the screws and started slowly rotating the motor. No disconnecting ribbons, not taking anything apart.
I'll call a local service I found. Though at this point I wouldn't mind sending the machine somewhere where proper calibration can be done.

[dellsam34]

Did you hold the head while spinning and lock it up, That will certainly pop the circuit protection fuse for the motor. Rule of thumb, never mess with something you're not sure if you can do. At this point you don't have a choice but to send it to someone who is qualified to perform such repairs, It is not going to be cheap but better than buying another unit that may or may not work.

[dellsam34]

If you have the skills to troubleshoot circuit boards with a voltmeter you can do some basic checks, Looking at the switched power PCB schematic, there are 4 circuit protection components:

CP5301 ?V P# ICP-N15
CP5302 5V P# ICP-N38
CP5303 5.8V P# ICP-N38
CP5304 6V P# ICP-N20

CP5302 looks like the one feeding one of the pins (5V) of the drum motor, Probe both legs of the CP, If one leg has voltage but the other doesn't, that means it's blown and needs to be replaced. You can do the same thing with each one of them.

[SF01]

Did you hold the head while spinning and lock it up, That will certainly pop the circuit protection fuse for the motor. Rule of thumb, never mess with something you're not sure if you can do. At this point you don't have a choice but to send it to someone who is qualified to perform such repairs, It is not going to be cheap but better than buying another unit that may or may not work.

I don't recall touching the drum, but that's too late now. I'll check with a local servicing offer. If not I got a contact to someone in another country allegedly skilled in calibration of broadacast equipment.

[oln]

Switch point can be adjusted if it has been tempered with before, I made a video on how to adjust it on a JVC machine, Video99.co.uk also made a recent video on how to adjust it on a Samsung machine. Pretty much any VCR with a head drum motor on top is adjusted the same way.

Just to note, on most vcrs you want to use the electronic adjustment functionality - trim pot on older vcrs and menu/button on newer ones. Only adjust head nut if that's not possible either due to lack of JVC service remote, or if you are dealing with a newer vcr with auto adjust function where the head switch is too far off for the auto adjust to be able to do it's job. The auto adjust on some models like panasonics very narrow range they can adjust from before they give up and complain, while the Samsungs are able to auto-adjust the head switch from like the middle of the picture to correct position with no issue.

If it's fine on pre-recorded tapes, and only off on new self-recordings, it's likely not the head switch point that's off but something else with the servo lock during recording that's wrong and adjusting head switching point will likely not help.

[dellsam34]

Correct, However if the switch point is way off mechanically you can only do so much with the trimpot, Kind of like tracking center point, If it is slightly off, the electronic automatic tracking can still work, albeit will not be in the center anymore, but if mechanically goes way off due to loose P guides or something mechanical, there is nothing can be done electronically.

As I explained in my video description this process is not meant to replace the manufacturer's calibration in the service manual, It can however be used mainly for oddball tapes or if the head is being taken a part or replaced and one doesn't want to alter the factory trimpot position.

[SF01]

I left it at the service point, the ealiest the guy can take a look at it is January, so in the meantime I'm on a hunt for a replacement unit, as I'm behind schedule with duplication and I probably should redo the tapes that I recentely did, at least none have been sent to buyers and creators.