Reassembling a DVCPRO Cassette
If you ever have cause to tear apart one of these digital video cassettes, you probably want to get it back together again in good working condition. Just in case you’ve spilled the guts of one of these cassettes all over your workbench and you can’t seem to figure out where all those little pieces go, this page can help!
You may click on the encircled portions of the image for a closer view of the component in question, or choose one of these links for further information:
- Record tab — The sliding tab at the rear of cassette housing used to prevent accidental erasure of information stored on the tape
- Door lock — A small tab with catches that prevent the cassette door from opening unnecessarily
- Back door guide — A small track molded into the cassette shell which guides the rear door away from the tape when the front door is opened
- Centre post cover — A transparent dust cover which keeps the inside tape compartment free of contaminants while allowing the tape end sensor LEDs to function through it
- Door lock spring — The folded metal piece that keeps the door lock firmly in place on one side of the cassette
- Reel brake spring — A metal coil spring which puts pressure on the reel brake mechanism to keep the reels from rotating unnecessarily
- Top cassette shell details
Record/Protect Tab
The record tab is shown here against the backdrop of it natural resting place inside the DVCPRO cassette. Just beside where the record tab fits into the shell is a plastic insert which covers the four slotted openings molded into the lower cassette shell. This insert fits into the lower shell so that the narrow end blocks the four slots which are below the record tab opening of the top shell.
The record tab itself fits into the lower shell such that the ramp-shaped portion — the portion having a U-shaped hole in it — is facing down into the bottom of the shell, and the ramp-shaped area fits into a similarly shaped receiving area molded into the shell.
Door Lock Mechanism
One of the plastic door lock mechanisms is shown here at the right side of the cassette. The locking tab has two small nibs protruding from its top. These nibs nestle in to dome-shaped depressions molded into the bottom shell. The back side of the door lock is the flattest portion of the tab, and this is the part that rests against the cassette shell, while the angular protrusions on the opposite end interface with the door when assembled.
On this side of the cassette, the door lock spring is fitted into the top cassette shell, providing resistance to keep the lock in place and also to return the door to a closed position upon tape ejection from a machine.
Rear Door Guide
Pointed to by the red arrow in the image, the rear door guide tracks are molded into the cassette shell on both sides. The two molded pieces are almost directly inline with the centre of the tape reels when they are seated inside the shell. When all the small pieces are in place within the cassette shell, the top half of the shell is gently fitted into place. There are two small protrusions on the rear door which must be fitted into both sides of the rear door guide before the cassette can be fully reassembled with screws.
The two molded pieces which form the rear door guide also are the only two tape guides within the cassette. When the reels are properly seated in the shell, the tape must span from one guide to the other. This image depcits the path the tape must take to ensure proper operation. The slack can be taken up by turning one of the reels in the appropriate direction, and proper tension will be maintained by the reel brake, if it is properly installed.
Centre Post Hole Cover
Front and centre inside the DVCPRO cassette is the centre post cover. When the tape is inside a DVCPRO machine, LEDs on a post inside the machine peek into the cassette via the hole that is molded into the bottom shell, centred between the reels. The LEDs combine with sensors placed just outside the cassette on both sides to form an end of tape sensor system which stops the reel motors from pulling the tape too tightly at the end of a fast forward or reverse operation.
The end of tape sensor mechanism is the reason the centre post hole cover is made of transparent plastic. The cover piece is mostly circular at the top, with two short and straight “legs” that protrude downward. These legs more or less seal the cassette from dust and contamination and maintain a line-of-sight for the end of tape sensors. The cover has one flat edge which lines up with two small and flat moldings in the bottom cassette cover, making it easy to line the cover up and seat it in flush with the top of the post hole molding.
Door Locking Spring
The left side door lock mechanism of the cassette — as viewed from the top, rear — has its own spring made of folded metal. The purpose to this piece of metal is to provide resistance for the door locking tab which ensures that the door will not open through normal handling of the cassette.
The metal spring itself is folded in four places — two for the spring’s lever, and two for its “legs”. The top is the trapezoidal-shaped surface, which would place the legs pointing downward, and the spring lever protruding outward. The lever should point toward the front of the cassette shell, with the legs resting on the bottom. It is placed in the bottom cassette shell so that it straddles a molded cross-member right up front near the door lock tab. The lever projects forward to rest on top of the door lock tab.
Reel Braking Assembly
The reel brake assembly consists of two components: the brake and the spring. The spring is a metal coil spring which rests against the back end of the cassette shells at its one end, and centers over a guide pin molded into the brake at the other. The spring applies constant forward pressure on the brake mechanism, which in turn prevents the reels from spinning freely inside the cassette while it is not in use.
The brake is a plastic piece with two very thin arms which interlock with teeth molded into each of the two reels to provide the braking action. When inside a machine, the brake is forced toward the back of the cassette by the machine. A post in the machine interfaces with a ramp that is molded into the bottom side of the brake which causes the brake to be released as the cassette is lowered into position on the tape transport. The brake piece is oriented inside the cassette such that this ramp part is facing the rectangular hole in the lower cassette shell and the braking arms extend toward the front of the cassette and rest against the reels. The toothed portion of the reels therefore must face downward, toward the bottom of the cassette so as lock with the brake.
Top Cassette Shell
The top half of the cassette is the part that holds the doors in place, houses the tape viewing window and also the door closing spring and reel stabilizer springs.
The reel stabilizer springs are two arms of a single piece of metal attached directly to the top shell. The centres of the tape reels contact the centres of these two arms when the cassette is loaded in a machine, and the plastic to metal contact makes for a bearing type surface that needs no lubrication.
The door spring is just barely visible at the left edge of the shell as seen in this image. Its primary function is to close the front door upon tape ejection from a machine and keep it closed while the cassette is not in use. Secondarily, it keeps one of the door locks engaged properly to ensure the doors cannot be easily opened during transport.
All of the pieces in the top shell are more or less permanently attached to one another, though the doors can be removed with the careful application of force at its hinges. If the spring should come loose, it is simple to manoeuvre it underneath the catch in the front door, and also under the catch in the shell molding which is ever so slightly to the side of the door piece. The spring’s rear-facing arm is approximately one quarter of an inch (or 6 millimetres) long beyond the catch molded into the shell. This is simply because it also acts as a retention mechanism for the door lock for that side.
