JVC Camcorder (1994) – part 3

 

After removing the lens assembly and rather a lot of plastic pieces we are left with the core tape mechanical mechanism attached to the main electronics PCB.

 

 

Tape Mechanism

Lets start with the mechanical assembly, I find the mechanical design of these to be staggeringly complicated. I guess they evolved from reel to reel tape systems, but how they designed these systems with hundreds of moving parts is fascinating. This is the full assembly prior to my teardown.  When the cassette is inserted the cover is opened, there are two guide pins that move to wrap around the read/write head.  In standard VHS it wraps around 180° for VHS-C it wraps around 270° giving it higher density and allowing extended recording/playback time.


 

 

I removed the tape holder/eject assembly.

 

 

 

 

And then four screws (Of nearly 60 in total) that hold the audio read head to the chassis.

 

On the rear of the chassis you have the tape motor connected by a rubber belt to the drive cogs, and a pair of complex flex cables.

 

The left (complex) flex cable contains a microswitch that monitors the read/write protection notch on the cassette (VHS cassettes had a slidable tab on their rear that enabled you to set write protection).

 

 

 

The one on the right has a connector with 5  multi-pin connections to the read/write head motor.

 

After removing countless screws and plastic cogs, I extracted the read/write head and motor.

 

This is the motor assembled with a collar secured with an allan bolt holding it together.  These are mounted at an angle and the tape takes a helical path around them maximizing the information that can be written across the width of the tape. Known as an Helical Scan

 

 

 

Top of the read/write head.

 

With the collar undone the two halves slide apart. There is a great bearing in these, if you spin one half it will spin for a long time with very little friction.

 

The base contains 12 windings for the induction motor which apparently spins at 1800rpm.

 

 

 

 

And this is the top half showing the 4 read/write heads that appear identical, other than they are marked green or red (suggesting they may be balanced).  What I don’t understand is what the extra 5th head is for?  It appears similar to the other four, but using non-coated wire (The other 4 heads have red coated wire) with a few extra turns. After researching this a bit I believe it is a Flying Erase Head

The heads are positioned very precisely such that they extend past the edge of the drum only a few microns.  They are essentially a piece of ferrite with a metal coil winding around two sections.  Here is a microscope image  (This is a composite image stitched and focus stacked (4 images each a stack of 10 images)

There are two other motors on the assembly.  The tape drive motor is a self contained unit

And in one corner is another small motor that I think drives the tape alignment pins via a complex array of cogs.

I gave up tearing it down to the chassis plate at this pint with ~10 metal and plastic cogs still attached.  Laying out all the parts, there are over 60+ individual parts and 50+ screws in this assembly

One more part still to come, I will look at the main PC board and some of the identifiable chips next.

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