I have a VHS-C camcorder that has a lot of trouble keeping constant speed for the main tape motor (even with the battery fully charged). Most of the time it's way too fast (similar to fast forwarding), but at the beginning of the tape it's often too slow (I'm guessing the new-ish tape is too heavy for the 1993 thing? Though it's the standard 30min one). It works correctly once in a blue moon. It doesn't seem like it's an LP/SP issue, considering it sometimes works and, most importantly, it looks way too fast even for SP (also, it's sped up even during recording). I opened half of the camcorder to see if there are any obvious mechanical issues to no luck.
So here comes the question: how is the speed for play/fast forwarding regulated? Are there different pins/voltages for the motor itself, or does this weird rubbery roller press and slow down the tape? Or should there be gears with different diameter that the mechanism switches between, to get the appropriate reel speed? I'll probably risk opening the whole thing up to try and fix it, but at least I'd like to know what to look for. Last time I opened up a VCR was around 2004 :(
EDIT: it's probably not a tracking issue either as it's supposed to adjust the tape of the head and not the reels (correct me if I'm wrong). I tried cleaning everything
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\$\begingroup\$ I changed my old VHS tape thing for a new digital PVR a long time ago and now I have a second PVR. Why don't you do the same? \$\endgroup\$– AudioguruCommented Apr 10, 2019 at 15:04
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1\$\begingroup\$ @Audioguru: "camcorder" means "camera + recorder". In other words, it isn't just a recorder. \$\endgroup\$– Dave TweedCommented Apr 10, 2019 at 15:06
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\$\begingroup\$ @audioguru: I use a DSLR as my main camera and camcorder, I just have this old analog one for artistic lo-fi purposes! \$\endgroup\$– MariaCommented Apr 10, 2019 at 15:08
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1\$\begingroup\$ They use a PLL method of servo speed control, perhaps many critical adjustments . Pls look for a service manual \$\endgroup\$– D.A.S.Commented Apr 10, 2019 at 15:16
1 Answer
Just like with audio tape recording, there is a capstan and pinch roller that controls the tape speed during recording and playback.
If the playback is faster than it should be, it means that either the tape is speeding up during playback, or it's slowing down during recording. The latter seems more likely, given your description.
This means that the tape is not being firmly gripped by the the capstan, and the usual causes of this are hardened rubber or a weak spring on the pinch roller.
To answer your side question, the different speeds are controlled electronically, by varying the speed of the capstan itself. During recording, the speed is locked to the frame rate of the incoming video signal (which, in a camcorder, is controlled by a crystal). The capstan motor and the head motor must be properly synchronized (to each other and to the incoming video signal) in order to lay down helical tracks on the tape correctly. During playback, the speed is controlled through a servomechanism that uses the sync track as a reference.
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\$\begingroup\$ Thanks a lot, this pretty much answers my question! \$\endgroup\$– MariaCommented Apr 10, 2019 at 15:11