Before you can repair a VCR, you need to understand the territory. This section deals with how a VCR's mechanical deck is laid out, the individual parts and what they do. Developing an understanding of how it all works together, goes a long way towards acquiring successful troubleshooting techniques.
The above two drawings show a VHS mechanical deck. Figure 1 - shows a vertical elevation while Figure 3 - shows a horizontal layout of the same deck. Both drawings use the same table Figure 2 - for parts identification. Because this is a general layout, your VCR may have more or fewer parts on the deck. The following discussion will describe the function of the above parts in detail. The order goes in the direction of the tape flow starting with the supply reel table.
Supply Reel Table (P) - This is the complex wheel structure that supports the supply reel inside the cassette. The center part goes up into splines inside the reel for a positive mechanical connection for transferring power and keeping the reel accurately centered. The reel table revolves around an axle called a spindle. On the spindle underneath the reel table, are spacers that always maintain the reel table's height accuracy. Problems - height gets misaligned by technicians who loose the spacers underneath it when they have it apart. In rare cases, it will make noises due to a lack of oil.
Supply Reel Brake (Q) - the supply reel brake is automatically applied at the end of all transport functions ( PLAY, REWIND, RECORD etc). It remains on while in STOP mode.
P1 Post (B) - the first thing the tape makes contact with after it leaves the cassette. It's the first part of a triad of components for tape tension regulation.
Tape Tension Arm (C) - this part works with two other stationary posts, P1 and P2, and a felt band that wraps around the supply reel table. By adjusting spring tension on the arm, the tension on the tape can be accurately adjusted. The tape tension is not real critical; VHS specifications call for 30 to 45 gram/centimeters on a Back Tension measuring cassette. Problems - the biggest problem is felt delaminating from the band.
br> P2 Post - the final part of the tape tension triad.
Full Erase Head (D) - this is an electro-magnet that erases everthing on the tape as it passes by. It is only used during the RECORD mode. Problems - extremely rare.
Impedance Roller (I) - helps smooth tape flow by putting a load on it. Most newer low end machines don't have this part.
Roller Guide (supply) (E) - This assembly travels on a lubricated slide track for wrapping tape around the video drum. It also has adjustments to position the tape height.
V-stop (supply) (Z) - this part is located at the end of the track that the Roller Guide travels on. It is carefully designed so that when the Roller Guide makes contact with it, the Roller Guide is held exactly vertical at a precise height. When fully loaded, the Roller Guides should be tight.
Video Drum (F) - this is the part that reads and writes video on the tape. The lower stationary part contains a servo motor that spins the upper drum with the video heads. Extreme care should be taken when working near video heads.
V-stop (takeup) (Z) - same as V-stop (supply) above.
Roller Guide (takeup) (G) - same as Roller Guide (supply) above.
ACE Head (H) - it stands for Audio-Control-Erase. This is a combined tape head assembly for recording and playing back audio and control pulses. It works exactly like the stationary head in an ordinary audio recorder. On the top edge of the tape, it records and plays back audio. On the bottom edge it does something a little different: it records and plays back control pulses. Control pulses are used to regulate the capstan speed. On newer VCRs they are also used for the real time counter. The erase part erases a narrow horizontal track on the tape to record the new audio information on without affecting the video.
P3 Post (J) - guides the tape to the capstan.
Capstan Shaft (K) - this is the rotating shaft that actually moves the tape through the VCR. It is powered by a servo motor (servo means very accurate speed control) so the video tracks on the tape can be synchronized with the spinning video drum for a stable picture.
Pinch Roller (L) - this is a rubber cylinder that presses the tape against the capstan shaft for traction.
Takeup Reel Brake (Q) - same as Supply Reel Brake above.
Takeup Reel Table (Y) - same as Supply Reel Table above.
Now that you understand the individual parts and what they do, lets look at how they work together. The Moving Mechanism consists of components that move when VCR is changing transport modes. Things like roller guides, pinch roller, brakes and the tape tension arm. Examples of mode changes might be going from PLAY to REWIND or from STOP to FAST FORWARD etc. The Tape Transport consists of components that move the tape.
Figure 1.
A - Supply Reel J - P3 Post S - Capstan Drive Belt B - P1 Post K - Capstan shaft T - Capstan Flywheel C - Tape Tension Arm L - Pinch Roller U - Clutch By Pass D - Full Erase Head M - Review Post V - Reel Belt E - Supply Roller Guide N - Capstan Motor W - Clutch F - Video Drum O - Takeup Reel X - Idler G - Takeup Roller Guide P - Supply Reel Table Y - Takeup Reel Table H - Audio-Control Head Q - Reel Brake Z - V-stop I - Impedance Roller R - Tape Tension Adjust
Figure 2. - Parts identification table.
Figure 3.
The above two drawings show a VHS mechanical deck. Figure 1 - shows a vertical elevation while Figure 3 - shows a horizontal layout of the same deck. Both drawings use the same table Figure 2 - for parts identification. Because this is a general layout, your VCR may have more or fewer parts on the deck. The following discussion will describe the function of the above parts in detail. The order goes in the direction of the tape flow starting with the supply reel table.
Supply Reel Table (P) - This is the complex wheel structure that supports the supply reel inside the cassette. The center part goes up into splines inside the reel for a positive mechanical connection for transferring power and keeping the reel accurately centered. The reel table revolves around an axle called a spindle. On the spindle underneath the reel table, are spacers that always maintain the reel table's height accuracy. Problems - height gets misaligned by technicians who loose the spacers underneath it when they have it apart. In rare cases, it will make noises due to a lack of oil.
Supply Reel Brake (Q) - the supply reel brake is automatically applied at the end of all transport functions ( PLAY, REWIND, RECORD etc). It remains on while in STOP mode.
P1 Post (B) - the first thing the tape makes contact with after it leaves the cassette. It's the first part of a triad of components for tape tension regulation.
Tape Tension Arm (C) - this part works with two other stationary posts, P1 and P2, and a felt band that wraps around the supply reel table. By adjusting spring tension on the arm, the tension on the tape can be accurately adjusted. The tape tension is not real critical; VHS specifications call for 30 to 45 gram/centimeters on a Back Tension measuring cassette. Problems - the biggest problem is felt delaminating from the band.
br> P2 Post - the final part of the tape tension triad.
Full Erase Head (D) - this is an electro-magnet that erases everthing on the tape as it passes by. It is only used during the RECORD mode. Problems - extremely rare.
Impedance Roller (I) - helps smooth tape flow by putting a load on it. Most newer low end machines don't have this part.
Roller Guide (supply) (E) - This assembly travels on a lubricated slide track for wrapping tape around the video drum. It also has adjustments to position the tape height.
V-stop (supply) (Z) - this part is located at the end of the track that the Roller Guide travels on. It is carefully designed so that when the Roller Guide makes contact with it, the Roller Guide is held exactly vertical at a precise height. When fully loaded, the Roller Guides should be tight.
Video Drum (F) - this is the part that reads and writes video on the tape. The lower stationary part contains a servo motor that spins the upper drum with the video heads. Extreme care should be taken when working near video heads.
V-stop (takeup) (Z) - same as V-stop (supply) above.
Roller Guide (takeup) (G) - same as Roller Guide (supply) above.
ACE Head (H) - it stands for Audio-Control-Erase. This is a combined tape head assembly for recording and playing back audio and control pulses. It works exactly like the stationary head in an ordinary audio recorder. On the top edge of the tape, it records and plays back audio. On the bottom edge it does something a little different: it records and plays back control pulses. Control pulses are used to regulate the capstan speed. On newer VCRs they are also used for the real time counter. The erase part erases a narrow horizontal track on the tape to record the new audio information on without affecting the video.
P3 Post (J) - guides the tape to the capstan.
Capstan Shaft (K) - this is the rotating shaft that actually moves the tape through the VCR. It is powered by a servo motor (servo means very accurate speed control) so the video tracks on the tape can be synchronized with the spinning video drum for a stable picture.
Pinch Roller (L) - this is a rubber cylinder that presses the tape against the capstan shaft for traction.
Takeup Reel Brake (Q) - same as Supply Reel Brake above.
Takeup Reel Table (Y) - same as Supply Reel Table above.
Now that you understand the individual parts and what they do, lets look at how they work together. The Moving Mechanism consists of components that move when VCR is changing transport modes. Things like roller guides, pinch roller, brakes and the tape tension arm. Examples of mode changes might be going from PLAY to REWIND or from STOP to FAST FORWARD etc. The Tape Transport consists of components that move the tape.
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