Troubleshooting The Ra-4 Chassis; Overview - Sony KDP-57XBR2 Training Manual

1. Features
Chapter 7 - Troubleshooting the RA-4 Chassis

Overview

The RA-4 chassis represented a great leap forward for Sony in the rear projection television market. One of its
most outstanding introductory features was the ability to perform line doubling of the standard 480i NTSC scan
rate. By doubling the scan horizontal scan rate to 960i, the annoying scan lines that were prevalent on these
large-screen sets were virtually eliminated. Not only is this chassis able to double the scan lines, but it also
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doubled the horizontal resolution by utilizing a new circuit known as the "Digital Reality Creator" or DRC . This
new circuit eliminated the "aliasing" that occurs when normal scan lines are simply doubled by making use of
pattern recognition technology to smooth out the jagged edges that would normally occur. This set was capable
of producing "near high definition" quality from NTSC video sources. Unfortunately, this chassis was only available
in two models (KP53/61XBR200) and these were relatively high-priced units, but it would set the precedent for
future designs.
The RA-4 was also the first chassis to introduce a fully digitally controlled convergence circuit, which allowed for
conventional adjustment methods via the remote control to allow the technician to perform "fine" touchup
adjustments at specific areas of the screen to provide excellent geometry and convergence control throughout
the entire screen area. These adjustments could then be written to memory and, by using special sensors
located behind the front bezel, allowed the customer to press a button and bring the convergence back to proper
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alignment. This feature is known as Flash Focus .
The picture-and-picture circuitry also received an upgrade, allowing the customer to scale the size of the main
and sub picture with the remote control. Channel previewing was another feature that would allow the customer
to view active channels around the perimeter of the main picture. This would be handled by a new circuit known
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as the "multi-Image driver" circuit or MID . With these new features added, the video processing became more
complex and practical methods are necessary to help isolate a failure.
This chassis also introduced an entirely new power supply design that deviated from the previous style. The dual
switching transistor design requiring the need for feedback was replaced with a new type that would function
more like a PWM supply, although frequency shifting would still be the core of the regulation concept. This
requires different troubleshooting approaches but the procedure is considerably easier.
The RA-4A would soon follow and, although it carried over the many of the new concepts of the RA-4 chassis, it
introduced a "high definition ready" version of the chassis that will be covered in another section.
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