TAPE PATH ALIGNMENT AND ELECTRICAL ADJUSTMENT
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Inside the circle above is the area where the tape path alignment takes place. Below it service progress tree found in the service manuals. It shows the order in sequence that different tests, checks and corrections should be performed. Tape path alignment is third down the list because first we must first verify the correct operation of several important areas. The whole process starts with verifying that the power supply and clock rate, shown flashing here to draw attention. Click on the picture. The first test is shown in the upper left (number 5). This is a very basic short test. A problem here requires a fix before any further testing can be done. The allowable loss to case ground is very small, only 0.75 volts. Next is the power supply check (number 5-1). If the power section can't supply the goods then nothing will work right. Too high a voltage and parts start to die. Too low and some things will refuse to operate. Each model is different and the illustration here it typical. If these two check out okay then the next test is for the clock rate. Not the one that tells the time but this one that tells everything when to do something. It is a reference used by the various integrated circuits to operate functions at the right time and on time. This one is the main clock and any variations of this rate are timed by this one. In the Betamax the clock is an electronic oscillator made of quartz. When electricity is applied to the crystal it vibrates the voltage at a very precise rate. This makes it an ideal timer form send messages and telling components when to do certain things. Testing its frequency rate is shown as a screen representation lower right using an oscilloscope (number 5-2). If it has a problem it must be corrected before the next step, the system control and servo check. Click on the picture. Now that the VCR has the power and knows how to use it the system control and servo check is next. This step verifies that the motors circuits are operating up to snuff. Click on the picture. Up first is checking the motor DC voltages. These are voltages used by the motors to move everything along. The testing method is shown upper left (number 5-3 items 1 and 2). You will notice that there is separate clock rate established for the motors to reference. The drum motor is a servo and it must spin at a regulated rate to make the picture correctly every time. There is an adjustment to meet a standard (number 5-3 item 3). Check and adjusting is illustrated lower left and top right. The same speed regiment is required of the capstan. The method is shown lower right (number 5-3 item 4). This adjustment insures that tracking will be centered and that the speed will be uniform from one Betamax to another. Once it is established that the tape can be moved and recorded the next item is the reel table motor. It does not need to as precise as the first two and it only requires that it operate. Its rate of rotation and operation will be determined by the function being requested. Operation of the Betamax in preparation of a tape path alignment goes like this. The loader is tricked into starting the loading cycle without a cassette. A motor pulls the receiver into the machine and stops at a pre-determined point. A switch is actuated and another motor threads the tape components into the path. Only this time there was no tape. Click the picture once again. Here is a close up of the components involved in sending the tape around the video drum. This is the tape entrance and the place the tape path alignment starts. The important items are indicated by the arrows. There are three guides here that control the tape. Starting with the number four guide it receives the tape from the number three guide that sets the bottom height for the tape as it travels on to the number five roller and collar. There is a tilt adjustment here to rock the number five so it is perpendicular. (The number two and three guides are not shown here because and they angle points and are not critical to entrance side of the tape.) The tape travels on and by the full erase head. The last adjustment is the number six guide and its height regulates the location of the tape as it engages the rail of the video drum. That rail is a ramp that the bottom of the tape rides in as it slides around the surface of the drum. There are three adjustments made with screws and the number five collar (the locking screw is used to secure the setting). These parts are threaded so they can be adjusted to produce the proper angle and position of the tape as it enters path around the video drum. One of the video heads can be seen sticking out of the slot just to the right of the number four guide. This opening, slightly larger than the rest of the drum slot, is where the heads first encounter the tape. This opening increases tape surface contact and helps with picture stability. Click on the picture again. Here are the exit side parts. Illustrated are the parts involved in adjusting the exit side of the tape envelope. The number seven guide sets the height of the tape coming from the drum rail and going to the ACE assembly. The number eight steadies the top of the tape as it travels on to the capstan. The number nine roller guide locates the tape on its way to the take up reel and when it travels in reverse play and scan. The screw in the center of the number nine guide is another set screw. The number ten guide is a pin and is not adjusted. The other adjusting screws and position adjustment are used to fine tune tape travel and location. The pinch roller has been removed in this close up to allow all the other parts to be seen. It would normally be pressed against the capstan. It is the capstan that pulls the tape through the machine. It plays an important part. It is designed to mount perpendicular to the number eight and nine guides. But with some high end model Betas the perpendicularity can be fine tuned. This is to make it run just as good in reverse as it does forward. Click here to see how this type capstan is adjusted. (You will be able to return.) Next, I want to call your attention to the list of categories below. Click on the picture and examine the sequence tree. The list of four items are links to the remaining steps in this alignment process. You can use these links to go directly to them, rather than do them in order. While the previous checks and adjustments needed to be done in order, these do not. For example a problem encountered in the picture processing of the video will normally have no affect on the normal audio. The exception would be the Betahi-fi audio, which is recorded inside the video signal. This method is covered in both of the audio sections. Below these links is a second list. It is for going directly to the items shown in the current browser window without having to close this panel. These two lists will be available throughout this refurbishing and repair discussion. They are intended as a navigational tool by helping to make information available as easily as possible. Video and audio are the next subjects up on the tree but first comes the tape path alignment. Now that all the parts and adjustments have been identified it is time to load a tape and see how the VCR behaves. To go to the next step, the PRELIMINARY CHECKS click here.
Remaining categories in the sequence tree: To go to the other subjects covered in this section: ©Misterßetamax go to homepage |
