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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 15th Apr 2021, 9:00 pm   #1
hillsrob
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Default VHS Tape Path Alignment

Hi everyone. I'm new to this group but getting back into working on video cassette recorders which I last dabbled in back in the 1970s and 80s. I've pulled an old JVC HR3300EK out of the loft and after giving it a good clean and replacing all of the belts I was surprised to find it worked almost perfectly. The only problem appeared to be a slight tape path alignment issue with a noise bar at the bottom of the screen and the one or two near the top. I did what we so often do these days and found a very useful YouTube guide to adjusting the main head entry and exit guide poles. With just a couple of minor tweaks it plays most tapes offered perfectly and tracks pretty closely to the standard.

I have the full service manual for this machine and I was surprised to find that the only reference to adjusting these guide poles is the advice NOT TO!

I'm just curious if this rule prevailed throughout the VHS service lifetime or if it became common practice to give these guide poles a final tweak? Obviously the job is best tackled with the aid of a scope but my Tektronix 545B went to the tip many years ago.
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Old 15th Apr 2021, 9:23 pm   #2
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Default Re: VHS Tape Path Alignment

The problem is, very often you need to look at the whole tape path, as one adjustment is often dependent on others being correct. Entry and exit guides, and their travel/endstops. A/C head, then there are things like clutch and pinch roller which can also affect the 'tracking'. Then if someone's been twiddling there are things like FM level and head switch point.

In your case, you had noise both at top and bottom of the picture, that suggests someone may have been 'at it'! It's not very usual for both guides to go out of alignment together.

Incidentally, if a machine has been diddled with, you can often get an initial 'ballpark' adjustment by using a pre-recorded tape from a well known production company (not kids' cartoons as these apparently often used B grade tape), watching if the tape wrinkles on the lower drum and adjusting the guide back from there. That should at least get rid of the multiple fixed noise lines. Then its a case of greater precision adjustments (/test tapes /scope) and finally centring the tracking control with the A/C head.
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Last edited by ben; 15th Apr 2021 at 9:28 pm.
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Old 15th Apr 2021, 9:45 pm   #3
hillsrob
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Default Re: VHS Tape Path Alignment

Thanks for your quick response Ben. I take your point about viewing the tape path as a whole. I do have a few good quality pre-recorded tapes and these play well with the tracking control at the 'click' position. I don't intend to do anything major to it as I'm more than happy that it's working again.
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Old 16th Apr 2021, 5:34 am   #4
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Default Re: VHS Tape Path Alignment

Hi

Check the pinch roller before adjust the tape path
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Old 16th Apr 2021, 6:37 pm   #5
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Default Re: VHS Tape Path Alignment

dont forget to secure the tape guides ,once you have reset them .1.7mm hex key if i remember .same with most vhs makes except mitsubishi which dont have a lock. we used to use screwlock with them.
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Old 16th Apr 2021, 6:58 pm   #6
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Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by vhs doctor View Post
Hi

Check the pinch roller before adjust the tape path
Good advice thanks. The pinch roller appears to be in good shape but it may have hardened in 45 years! In the old days I would have replaced it routinely but spares are in very short supply now.

I guess the answer to my question is only ever adjust the guide rollers if all the other alignment checks have been made and adjusted correctly if required. This obviously includes checking the condition of the pinch roller.
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Old 16th Apr 2021, 7:58 pm   #7
vhs doctor
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Default Re: VHS Tape Path Alignment

Check this

https://www.donberg.ie/catalogue/vid...ers/13050.html

In my opinion if your VCR had the factory adjustments, do not adjust anything. It requires special tools such as alighment tapes, generators etc.
Your VCR was one from the first VCR mechanisms. These mechanims are not high speed and they dont have full loading tape during REW and FF (the tape unloaded from the drum). It is difficult misalignment of tape guides

Last edited by vhs doctor; 16th Apr 2021 at 8:15 pm.
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Old 17th Apr 2021, 5:01 pm   #8
hillsrob
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Default Re: VHS Tape Path Alignment

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Originally Posted by gallowfields View Post
dont forget to secure the tape guides ,once you have reset them .1.7mm hex key if i remember .same with most vhs makes except mitsubishi which dont have a lock. we used to use screwlock with them.
Hi gallowfields, I think I used the wrong terminology in my original post. I meant the supply and take up guide rollers (either side of the head drum). I haven't needed to move the supply or take-up guide poles which are locked as you describe.
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Old 17th Apr 2021, 5:06 pm   #9
hillsrob
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Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by vhs doctor View Post
Check this

https://www.donberg.ie/catalogue/vid...ers/13050.html

In my opinion if your VCR had the factory adjustments, do not adjust anything. It requires special tools such as alighment tapes, generators etc.
Your VCR was one from the first VCR mechanisms. These mechanims are not high speed and they dont have full loading tape during REW and FF (the tape unloaded from the drum). It is difficult misalignment of tape guides
Thanks again for you good advice. I am starting to collect together the required equipment and alignment jigs. See attached. My next purchase will be a suitable scope.
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Old 17th Apr 2021, 6:51 pm   #10
dj_fivos_sak
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Default Re: VHS Tape Path Alignment

You can usually find out if the P2 (entrance side) or P3 (exit side) guide posts are out of alignment by simply pressing on them with your finger while the tape is playing. A common problem with early JVC machines is the metal base where the pinch roller is mounted can flex and bend. This can easily happen if someone pushes too hard with a screwdriver to remove the screw that's holding the pinch roller in place. This will cause the tape to ride upwards on the capstan shaft, then the control head will miss the control track and the top edge of the tape will get screwed up. So you need to pay extra attention when trying to replace the pinch roller on one of these machines.

Fivos
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Old 17th Apr 2021, 10:28 pm   #11
hillsrob
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Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by dj_fivos_sak View Post
You can usually find out if the P2 (entrance side) or P3 (exit side) guide posts are out of alignment by simply pressing on them with your finger while the tape is playing. A common problem with early JVC machines is the metal base where the pinch roller is mounted can flex and bend. This can easily happen if someone pushes too hard with a screwdriver to remove the screw that's holding the pinch roller in place. This will cause the tape to ride upwards on the capstan shaft, then the control head will miss the control track and the top edge of the tape will get screwed up. So you need to pay extra attention when trying to replace the pinch roller on one of these machines.

Fivos
Thanks Fivos for some more useful tips for my notes. I assume P2 and P3 are the supply and take-up guide 'rollers' either side of the head drum with P1 and P4 being the supply and take-up guide 'poles' using JVC's terminology?

I didn't start well by getting this wrong in my original post. I'll try to edit it.
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Old 17th Apr 2021, 11:24 pm   #12
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Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by hillsrob View Post
Quote:
Originally Posted by dj_fivos_sak View Post
You can usually find out if the P2 (entrance side) or P3 (exit side) guide posts are out of alignment by simply pressing on them with your finger while the tape is playing. A common problem with early JVC machines is the metal base where the pinch roller is mounted can flex and bend. This can easily happen if someone pushes too hard with a screwdriver to remove the screw that's holding the pinch roller in place. This will cause the tape to ride upwards on the capstan shaft, then the control head will miss the control track and the top edge of the tape will get screwed up. So you need to pay extra attention when trying to replace the pinch roller on one of these machines.

Fivos
Thanks Fivos for some more useful tips for my notes. I assume P2 and P3 are the supply and take-up guide 'rollers' either side of the head drum with P1 and P4 being the supply and take-up guide 'poles' using JVC's terminology?

I didn't start well by getting this wrong in my original post. I'll try to edit it.
The P1 guide is the stationary guide right before the full erase head (called supply guide pole in JVC's service manuals). The P2 guide is called supply guide roller in the manual, the P3 guide is called take-up guide roller, and the P4 guide, the one right after the audio/control head, is called take-up guide pole. Like the P1 guide, the P4 guide is also stationary.
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Old 18th Apr 2021, 8:38 am   #13
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Default Re: VHS Tape Path Alignment

Of course doing Sony machines we only saw Beta's, the 8080's. But I was taking repairs in as jobs on the side. We used to call them "Scotchers", Never knew why they were given that name. Of course with Beta's you needed an eccentricity gauge, my eyesight was very good and I confess on occasions, to do it without. All this look for maximum FM from the heads seemed a waste of time, the tv screen told it all. When LP came out things were a little more tricky but we found with a good pre-recorded tape perfectly good results could be had by viewing the screen. Years on I think back at the practises we used to get up to, but I still got a good living out of the game, I loved the "phantom twiddlers", happy days.
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Old 18th Apr 2021, 12:40 pm   #14
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Default Re: VHS Tape Path Alignment

Post #6 here outlines the basic procedure I used to use for alignment of a deck.

https://www.vintage-radio.net/forum/...70&postcount=6
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Old 18th Apr 2021, 9:10 pm   #15
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Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by toshiba tony View Post
Of course doing Sony machines we only saw Beta's, the 8080's. But I was taking repairs in as jobs on the side. We used to call them "Scotchers", Never knew why they were given that name. Of course with Beta's you needed an eccentricity gauge, my eyesight was very good and I confess on occasions, to do it without. All this look for maximum FM from the heads seemed a waste of time, the tv screen told it all. When LP came out things were a little more tricky but we found with a good pre-recorded tape perfectly good results could be had by viewing the screen. Years on I think back at the practises we used to get up to, but I still got a good living out of the game, I loved the "phantom twiddlers", happy days.
I have to say that I got into playing with VCRs in the 1970s quite by accident. I had a full time job as a senior test engineer with Decca Radar. I used to repair microphones and other equipment on the side for a company now known as Techlink. On one occasion the boss presented me with an Akai VS-9300G/EK which he claimed had never recorded well even though it played back tapes made on other machines and pre-recorded ones. I had the machine for several months before I finally discovered that a capacitor used only in the record path was missing! It had never been fitted.

I was a Beta fan and drooled over the C7. It wasn't until 1982 that I eventually bought my own C6. I still have it in the loft and will take a look at it soon. I also owned a Philips NICAM VHS machine which was total rubbish and one of my last VHS machines was a S-VHS ITT Nokia with a flying erase head, also now queued up for my attention in retirement.

I have a stack of 5 Akai machines from the early noughties that I bought to churn out copies of a dancing show that I had been commissioned to shoot on my Sony VX9000 and Canon XL1 DV/mini DV camcorders. The digital master was stored on a full size DV tape but the Sony camera was far too precious to be used to churn out one copy at a time.
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Old 18th Apr 2021, 9:13 pm   #16
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Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by Mooly View Post
Post #6 here outlines the basic procedure I used to use for alignment of a deck.

https://www.vintage-radio.net/forum/...70&postcount=6
Thanks for the link Mooly.
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Old 4th May 2021, 12:54 am   #17
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Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by hillsrob View Post
Quote:
Originally Posted by vhs doctor View Post
Hi

Check the pinch roller before adjust the tape path
The pinch roller appears to be in good shape but it may have hardened in 45 years! In the old days I would have replaced it routinely but spares are in very short supply now.
I'd second pinch roller as a start as well. I did a couple of VCR ones a few years ago by sticking a few varying grades of fine emery to a flat piece of wood then mounting the pinch roller in a cordless drill using a long thin bolt. If you are careful you can gently roughen the surface. Then, give it a few coats of Rubber Renue.

Does everybody else miss what used to be Seme (Small Elephant, Medium Elephant) too?

My other thought was dried/solidified grease in the V stops. Given the age of the machine, if there is a hard buildup of grease in them, the roller guides might not be making it fully home which could mean the heads are just missing the start and end of the scan on the tape.
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Old 4th May 2021, 1:29 pm   #18
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Does everybody else miss what used to be Seme (Small Elephant, Medium Elephant) too?
Had many happy dealing with Bob Tanoch (SEME rep) and Bill Edwards (from CHS)

Bet you haven't got one of these, a SEME tie:

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Old 6th May 2021, 7:34 pm   #19
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Had many happy dealing with Bob Tanoch (SEME rep) and Bill Edwards (from CHS)

Bet you haven't got one of these, a SEME tie.
Oh wow! A friend of mine (S/H HiFi dealer/repairer) had one... I think I might have the first CD-ROM catalogue they released somewhere!

CHS - Used to get quite a lot of Denon DJ spares off them back in the day. Didn't they close a couple of years ago?
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Old 11th May 2021, 12:07 pm   #20
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Default Re: VHS Tape Path Alignment

If you have noise at both the top and bottom of the picture it suggests that the head to tape contact is poor at the beginning and end of the wrap, this was often caused by low tape back-tension. The back tension is provided by a brake band around the base of the supply spool and the tension is controlled by a guide lever /post that is on the left of the mechanism normally between the first fixed guide as the tape comes out of the cassette and the erase head. Two possibilities, one is that the pivot for that guide lever is gummed up so the guide is not free to move, the other is that the felt lining has fallen off the brake band, both possibilities are equally likely.

I would say twiddling with the entry and exit guides on the drum is a bad idea as the don't tend to go out of adjustment without some human help and re-aligning them requires an oscilloscope and ideally a proper alignment tape to get the envelope flat. As someone has already said, the adjustments affect each other and you cannot really gauge what is happening from a picture alone.
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