There are basically two types of cassette loading systems; front load and top load. In the late 70's and early 80's all VCRs manufactured were top loaders. Little by little they all gave way to front loaders; and since the mid 80's, the front loader has been dominant. For that reason, this discussion will focus on the front load type.
The good thing about working with cassette carriages is that the whole thing can be replaced easily and inexpensively (usually). The cassette carriage is an independent unit that can be removed. By removing a few screws (usually 4) and one electrical connector, the whole thing comes out. Some carriages use 2 screws and 2 hooks instead. If this is the case, after you remove the screws, you will have to pull the carriage forward or back depending on which way the hooks are facing in order to free it.
Normal Carriage Operation
Cassette Carriage Problems
Cassette Carriage Symptoms
Normal Carriage Operation
The first thing that happens after a cassette is inserted, the "cassette lid lock" is released by a plunger located on the carriage by the right side of the cassette; this allows the cassette lid to open. In event you run into a binding situation, check to see if the lid is opening. If not, there could be a problem with this plunger or the blade that actually pries the lid open.
Also the cassette tray release pins are retracted allowing the mechanism to travel forward until a switch is tripped to tell the CPU to turn on the load motor. Under power, the cassette travels forward and then down until the stop switch is tripped telling the CPU to shut off the power. Also on the way down, the cassette lid opens and the cassette lands on the gaging pins with Roller Guides and tape tension arm behind the magnetic tape. There are four gaging pins; the two front pins have flat tops to support the cassette while the rear pins are also pointed which serve to accurately align the cassette's position on center. All four pins accurately hold the cassette level at a specified height.
An infra red lamp goes up into the center hole in the bottom of the cassette; this works with the tape end sensors. In the rear, center of the cassette, another pin goes up to release the cassette's internal brakes.
A significant amount of spring tension remains on the cassette as long as it is loaded to firmly hold it down on the gaging pins. You should be able to press down on the cassette with your hand and feel no movement.
Cassette Carriage Problems
Cassette carriage problems can be divided into four areas:
- Mechanical defects - something physically broken on the carriage. Gears are the biggest offenders; they can even be unnoticeably worn, jump a tooth and cause a timing problem.
- Power supply defects - If the VCRs power supply is defective, the carriage can't get the electricity it needs to operate.
- Sensor defects (most VCRs use switches to sense position) - if a sensor is not being tripped, the CPU does not know it and therefore can't respond.
- Foreign objects caught in the works - small kids are famous for putting things in VCRs. Even if you don't have kids, be aware of the fact that even a label coming off a cassette is more than enough to stop a carriage dead in it's tracks.
The following requires some knowledge of electronics.
Most VCR carriages have two switches (or sensors) on them to sense cassette tray position; cassette up and cassette down. One wire leaves each switch to go to the CPU.
- With no cassette loaded, both switches send 0 volts to the CPU.
- When pushing a cassette in trips the cassette up switch, that wire now has 5 volts.
- When the cassette travels further, both wires again are 0 volts.
- When cassette tray hits the cassette down switch, that wire now has 5 volts.
The CPU can tell by these two wires what the loading status is for the cassette carriage. With a voltmeter, you can check these voltages for proper switch operation. If the cassette tray won't move on it's own, you can hand cycle it.
If you gently push a cassette in to trip the cassette up switch and nothing happens, do the voltage checks above. If that is okay, next you can measure the voltage on the motor. Place both voltmeter probes on the two motor wires. Insert the cassette and measure the voltage. It's important to make this measurement immediately because the CPU may shut the power off if something isn't right. If you have 6 to 12 volts, the motor is probably defective. If you have no voltage, the motor driver chip or power supply circuits may be defective.
Another test for the motor is to connect a 9 volt battery to it; unhook the existing wires first. As a precaution, hand cycle the carriage to the middle position because you don't know which way it will go when the battery is connected. Also be aware of the fact the motor will not automatically stop as the cassette tray gets to the end of it's travel when connected to a battery. Be sure and disconnect your temporary power before the cassette gets there or you may have a crash. Of course if nothing happens when the battery is connected, the motor is defective.
Cassette Carriage Symptoms
- VCR immediately ejects cassette you just inserted.
- You hear a clicking noise when power is applied or inserting a cassette.
- Cassette tray on carriage is crooked. If you are lucky, maybe a carriage gear just jumped a tooth.
- Cassette does not go all the way down.
- Cassette does not seat firmly on gaging pins after loading. Carriage may have insufficient travel or spring tension to hold it down. This will eat tapes.
- You see broken pieces in carriage assembly.
- Cassette binds, or does not go in when trying to insert. Something may have squashed carriage slot from the top.
- Cassette binds or gets stuck while loading under power.
- Cassette does not eject all the way.
- Cassette lid does not open. Cassette opener spring may have sprung.
- Cassette motor is defective.
- Someone forcibly removed a cassette that would not eject.
Any of the above is strong evidence the cassette carriage is defective. In cases where the carriage is powered by the moving mechanism motor, there is also some possibility that the chassis gear that drives the carriage may also be defective.
For beginners, it's an easy job to replace the entire carriage assembly. The task is easy on most VCRs. For those who are more experienced or on a tight budget, you might want to see if you can repair it. This is not always possible, even for experts. Some manufacturers don't even supply individual parts, just complete assemblies.
In binding situations, the carriage may have been bent by some heavy object on top of the VCR. Often, it can be bent back easily. Apply pressure to open the slot up until both top and bottom slot plates are parallel. Check to see that a cassette now slides in and out freely.
In cases of broken parts, see if they can be repaired or bonded if replacements are not available. That may save you the cost of a new carriage.
In cases of crooked cassette trays, you might be able to fix it by realigning the gears on both ends so they are equal.
|
All Rights Reserved |