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Old 10-06-2018, 08:17 AM
stragulus stragulus is offline
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RCA VDT-350 How to adjust tracking?

So, in a previous post I fixed mechanical issues with the broken loading gear. Now that tape loads and unloads correctly, it's time to address other issues. Everything seems to work fine, but the picture doesn't seem to track well. Depending on the tape, parts of it are white noise. I *think* the heads are ok though, as the picture that is not white noise looks very good and accurate. Better than the VCR I had back in the day.

I'm not sure if it's a tracking issue or something else. I cleaned the tape pathway with isopropyl alcohol, put some rubber renew on the idler wheels / pinch roller, fwd/rwd works, tape moves steadily during playback. The drum, I just cleaned the drum very carefully with the heads always far far away from the q-tip. I had to loosen the drum to fix the loading gear issue but it is screwed in rock solid and doesn't seem to have any play.

Does this thing have a tracking setting somewhere? Service manuals are also welcome...is it worth getting the Sam's photofacts for this one, or a similar model with the same chassis? I have never had one of those so I don't know if it's a comprehensive service manual or just a tutorial with poorly photocopied pictures.

Video of the best tape I could find (most are worse) below. Note that the 'green' screen is due to the recording, all but the top white noise part actually looks great in real life.

https://youtu.be/og7nsUoeQHM

EDIT: Found the tracking button, forgot the front flips open, duh.. anyway, doesn't have any effect on the white noise, it's centered which seems to be the right position for it. Also, the picture rolls vertically easily, though this *may* be due to my monitor, have to swap that one out to confirm.

Last edited by stragulus; 10-06-2018 at 08:25 AM.
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Old 10-07-2018, 04:29 PM
Ed in Tx's Avatar
Ed in Tx Ed in Tx is offline
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Most of the noise is at the top of the pic so that's the entry side of the tape to the head drum. Could be alignment, but if the entry and exit guide rollers are secure probably not. Or could be the back-tension band has worn out, the felt liner fell off the tension band or somesuch, seen that happen many times. Or maybe the tension spring that hooks onto the back-tension arm came off. Should be 20-30 grams of back-tension on the tape in play mode, measured with a Tentelometer. Without proper back-tension the tape will not be in good contact with the heads.
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Old 10-07-2018, 06:30 PM
stragulus stragulus is offline
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Quote:
Originally Posted by Ed in Tx View Post
Most of the noise is at the top of the pic so that's the entry side of the tape to the head drum. Could be alignment, but if the entry and exit guide rollers are secure probably not. Or could be the back-tension band has worn out, the felt liner fell off the tension band or somesuch, seen that happen many times. Or maybe the tension spring that hooks onto the back-tension arm came off. Should be 20-30 grams of back-tension on the tape in play mode, measured with a Tentelometer. Without proper back-tension the tape will not be in good contact with the heads.
This is the golden answer. I have read up on this topic now, and as you say, the back tension is the cause. The band has simply snapped. Is this made of common materials so I can attempt to recreate one? I don't have a tentelometer, but I read about a trick with v-hold to align image on top and below the blanking section which would probably be good enough for this sparingly used deck.
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Old 10-07-2018, 07:00 PM
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Ed in Tx Ed in Tx is offline
Zenith Walton My 1st TV
 
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You need to find a proper replacement tension band. Too critical for correct performance. As far as looking at the switching point down just above the vertical sync and adjusting it that way, that would depend on how accurate the dihedral alignment of the video heads was on both the machine the tape was recorded on and the machine playing back. That is how close to a perfect 180░ opposite they are on the drum to each other. A certain amount of tolerance was always "normal" and a little bit of difference where the switching point occurs was typical, but sometimes that alignment could be "off" enough to cause video "flagging" on a different machine playing back. Same tape would play fine on the machine it was recorded on. So do you by chance have a tape that was originally recorded on that VCR?
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Old 10-07-2018, 07:30 PM
Ed in Tx's Avatar
Ed in Tx Ed in Tx is offline
Zenith Walton My 1st TV
 
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I just looked at what VCR we're talking about, one of the RCA top-loaders made by Matsushita. Very common parts in a lot of those old machines whether Panasonic, RCA, Magnavox maybe a few more names I don't remember. The tension band would be the same. Find a junker somewhere with a good tension band in it. Or maybe someone here has one of those old machines in their collection..?
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Old 10-08-2018, 07:43 PM
stragulus stragulus is offline
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Ah, I was afraid of that answer I also don't have any tapes recorded for this device, just some prerecorded and blank tapes. That's a real shame, I love these giant old beasts. Guess I'll have to hunt for junkers, or use this one for parts..thanks.
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