Central Proccesing Unit

CPU - THE CENTRAL PROCESSING UNIT

THE BRAIN - If you think your computer is a marvel, take a look at what goes on inside your VCR. The CPU (central processing unit) is the heart of the VCR's command center. It controls everything that goes on inside. Not only does it accept signals from operating controls like the front panel buttons and remote control, but also monitors various sensors. If the output from any sensor changes, the CPU responds accordingly. For example, when a VCR gets to the end of the tape, the tape end sensor automatically tells the CPU to send the REWIND signal. The VCR starts rewinding without any help from you.

A VCR is actually a computer all by it self. Although very short of the computing power of a Pentium II, in fact it has no where near the capacity of an old IBM 8088, but it still has all the basics. It has:

a keyboard - the remote control and front panel buttons are the VCR's keyboard. The only difference between the keyboard on your computer and the keyboard on your VCR, is the number of buttons. Electronically, their functions are quite similar.
a monitor - the front panel display is the VCR's monitor, some also use OSD (on screen display)
a micro-processor
ROM (read only memory)
RAM (random acces memory) - mostly for channel and timer information storage
software - you never think of your VCR as having software, but the truth is, it wouldn't work without it. All of the software is a permanent part of the ROM. Although it may not be as complex as DOS or Windows, the software in your VCR is still far more complicated than you could ever imagine.

These components in your VCR function like a computer. It uses enable, control and data buses to move information around just like a computer does. But when it's malfunctioning, it can be a real chore to fix.

Trouble Shooting the CPU

As you might guess, the CPU is a little difficult for your average VCR owner to trouble shoot. It's also difficult for your average repair shop as well, so don't feel bad.

When it comes to CPU circuitry, a VCR can be much more difficult to trouble shoot than a computer. On a computer, you can swap out boards until the problem is located. But on a VCR, you don't have that luxury. The defective part must be isolated by using a systematic trouble shooting approach (which is beyond the scope of this website). Fortunately, these defects are rare. Thus, we will limit this section to a few basic checks.

First of all, check to make sure the CPU is not locked up. Remove the A.C. power plug for about a half a minute and then plug it back in. This sends a reset pulse to the CPU. If it was locked up, this procedure will fix it.

If unsuccessful, another thing you can try involves inputing data from the remote control or the front panel. Try the power button, changing channels, setting the clock or executing a function (PLAY, REWIND, etc). Also try loading or unloading a cassette. If anything happens, like the channel numbers increment or the clock changes, your CPU circuits are probably OK. Usually CPU circuits don't fail partially. They either work properly or they don't work at all. But the thing you have to look out for is that some VCRs have 2 or 3 CPUs in charge of different tasks. This can be sometimes confusing.

If nothing happens, the CPU is a possible suspect. But don't forget there are other things that are more likely to be causing the symptom - mainly power supply circuits.