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Troubleshooting VCR tape-loading problems ,' By PETER M. HANSEN One of the most common VCR problems is the inability to properly load a tape. Here's /how to troubleshoot ·VCR tape loading problems. Servicing a VCR that won't correctly load a tape is usually a simple exercise, provided you know what to look for. However, it is important that you clearly understand the difference between cassette loading problems and tape loading problems. Reprinted with perm1ss1on from Radio-Electronics magazine, September 1989 issue. (C) Copyright Gernsback Publications, Inc., 1989. 4 SILICON CHIP A cassette loading problem is where the cassette carriage assembly dcies not properly accept the cassette (the shell) into the VCR. A tape loading problem is when the tape is not properly extracted from the cassette once the cassette is fully seated inside the VCR. Fig.l shows the basic VCR components. You should become familiar with them before attempting any servicing but right now our main concern is the tape loading process. To be able to see the inter- nal components, you first have to remove the VCR's top cover and head shield. You may also have to remove the cassette carriage in order to fully access the components involved in the tape-loading process. Fig.2 shows the cassette carriage being removed from a VCR - there are usually four Phillips-head screws on the top of the assembly that secure it to the VCR chassis. Fig.3 shows the cassette carriage assembly by itself. The gear block and motor assembly on the right side of the carriage is the drive system. This is used in front-loading VCRs to load the cassette into the VCR when it is first inserted. The VCR's guide rollers and slant poles are what actually extract the tape from the cassette and guide it IMPEDANCE ROLLER VIDEO HEAD DRUM ASSEMBLY A.C.E. HEAD CAPSTAN SHAFT PINCH ROLLER of the mechanism, with the video drum behind it. Tape-loading components GUIDE ROLLERS/ SLANT POLES IDLER SUPPLY REELS BRAKES BELT FIG.1: THIS PICTURE SHOWS the major components on a VCR chassis. These basic mechanisms will be found in all VCRs. across the video-drum assembly. The motor is located either above or below the mechanism and is usually driven by an integrated circuit that receives the motor load and unload signals from the VCR's main microprocessor. Fig.4 shows a typical tape-load motor located on the bottom of the VCR's chassis. In Fig.5, we see a load motor that is located on the top The load gear train is almost invariably located on the bottom side of the VCR chassis. The load gear train is connected to the load motor via a belt (or worm gear) and associated linkage rods and connectors. The load-gear assemblies are made out of hard plastic and have one and sometimes two cam gears with grooves that contain a lubricant. Fig.6 shows a typical loading gear train on the bottom side of the chassis. To get at components on the underside of the chassis, first make sure that the power is off and the unit unplugged, then remove the VCR's bottom cover. There are usually several Phillips screws securing the bottom cover to the chassis. Next, you have to identify the screws that secure the PC board to the chassis. Often, there will be identifying arrows printed on the PC board to indicate which screws must be removed. If you remove the wrong ones you may be dismantling the wrong thing. In some VCRs you must remove the front panel in order to release the PC board. Usually, the frontpanel assembly (which contains the switches, display etc.) is secured to the chassis by small (fragile) plastic retaining tabs. Give the unit a close visual inspection before attempting to remove the board so that you FIG.2: THE CASSETTE CARRIAGE assembly is usually secured to the VCR chassis by four Phillips-head screws. across the video head/drum assembly. After you select play or record you will see the two guide posts start the tape-extraction process; the video drum starts to spin anticlockwise (it reaches 30 RPM in about 3 seconds) and the pinch roller starts its short movement towards the capstan shaft. It is the action of the pinch roller "pinching" the rotating capstan shaft that actually pulls the tape through the machine during play or record. Most recent VHS VCR's use a dedicated DC motor to load the tape FIG.3: THE GEAR BLOCK AND MOTOR ASSEMBLY on the righthand side of the carriage is the drive system that loads the cassette into the VCR. JANUARY 1990 . 5 FIG.4: THE LOAD MOTOR is typically located on the bottom side of the VCR's chassis. FIG.5: THIS LOAD MOTOR is located on top of the mechanism, near the video drum assembly. Worn rubber belts are a common cause of VCR problems . don't crack anything. Remember that any mistake can lead to a gr eat deal of added expense. With the VCR placed in its service position [see Fig. 7) you can closely observe the loading components during a tape load. To do that, plug in the unit, insert an inexpensive test tape and hit the play button. As soon a s you hit play, you should see movement of the loading gear train as well a s the guide posts. 6 SILICON CHIP On many units you'll also see the cam gear as it shifts position from "stop" to "fully loaded" . Sometimes a mirror placed on your workbench sur fa ce can help you see both sides of the VCR's loading mechanism simultaneously. Diagnosing malfunctions A very common malfunction in VCRs is cracked, dirty or worn [slippery) loading belts. A ma jor symptom of this problem is that when the operator selects play or record, the guide posts will start their path toward the "V" stoppers (the metal brackets situated at the end of the loading grooves) but they will not reach the end of their path. Often, they will appear to have completed the loading process but closer inspection reveals that they only complete about 90% or 95% of their travel. The loading posts will then start retracting back toward the stop position and the video drum will stop spinning. This type of fault is usually due to a bad loading belt. Because the slipping belt prevented the guide posts from travelling their full distance, the microprocessor did not receive what's called the "load complete", the "after load" or, more simply, the " AL" signal. Some of the older units have a small microswitch embedded in the load gear train that is activated when the load posts are fully extended. However, most newer VCRs have infrared sensors built into the cam-gear assembly that transmit the various mechanical load stages during the tape-load mode to the microprocessor. In an aborted tape-load attempt, you will also be able to see that the pinch roller does not come in contact with the capstan shaft. The pinch roller will come in contact with the capstan shaft only when the system microprocessor receives a load-complete signal. A simple test for a malfunctioning load belt is to "assist" the load process with your finger [see Fig.8). With the VCR in its service position and a tape inside the machine, select the play mode; you should have your index finger or thumb placed gently on the load-motor shaft. You will feel the rotation of the load motor shaft against your finger . Wait for the load process to be completed (when the load posts appear to have reached the end of their travel) and then "assist" the load process by manually turning the load motor shaft in the same direction as it was turning by itself. If the belt is bad, the action of your finger will most likely complete the load. The load-complete signal will now be received by the microprocessor which will issue the signal to FIG.6: THE LOADING GEAR train is often covered by a protective plastic guard that must be removed to give access for servicing. This gear train is on the bottom of the VCR's chassis. FIG.8: A MALFUNCTIONING LOAD BELT can be checked out by "assisting" the loading process with your finger. FIG.7: A VCR IN ITS SERVICE position. A mirror on your workbench surface will allow you to see both sides of the VCR simultaneously. activate the pinch roller. A bad belt should be replaced but sometimes you can extend its life a bit by cleaning the belt and applying some rubber revitaliser. Sometimes the lubricant that is applied to sliding tracks and to various components dries up and hardens. This can cause much added friction for the load components and may cause the load to be aborted. If that's the case, you have to dismantle the assembly, clean off the dried-up lubricant, and apply a fresh coat. It's best to use a solvent like acetone for removing the old lubricant. It is also a good idea to first take a photo or make a quick sketch of an assembly before dismantling it for cleaning, so that everything goes back correctly. Often, there will be small alignment arrows imprinted on the gears - pay careful attention to any arrows, as they must be exactly aligned during assembly. If the load belt appears to be good and there is no dried-up lubri- cant, then you have to inspect the load gears for any signs of cracking - especially hairline cracks. Any gears that show signs of cracking must be replaced. Note that load motors do not usually go bad but if there is excess freedom of shaft movement, or any signs of excessive friction in the motor, it may have to be replaced. Another quick test of the loading system is to perform a tape load by hand, with the unit unplugged and no tape inserted. That will provide an unobstructed view of the loading mechanisms as they operate. Also, the loading process will be greatly slowed down, so you'll be able to see - and perhaps even feel- exactly when a problem occurs. You can then determine which part might be causing it to happen. To perform the test, turn the load-motor shaft by hand and observe the unit's operation. Watch for freedom of movement of all of the mechanical components involved in the loading process, and check for any obstructions that may impede proper loading. ~ VHS Cleaning Kit Tape heads and guides should be kept clean and the best way to do that is to use a tape cleaner on a regular basis. This VHS tape cleaner from Trackmate is different from most in that, as well as the fabric cleaning tape, it has auxiliary brushes to clean the pinch roller and the grooves in the tape head drum . The latter are liable to clog up and thereby prevent proper tape contact with the drum and heads. A convenient marker pen applies the cleaning solution, to eliminate any spills. The Trackmate VHS cleaner is available from most department stores at $39.95 . JANUARY 1990 7