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5. RA-3/3A Deflection Circuits
to the horizontal deflection yoke return. One more waveform is required, however. Vertical rate parabolic
correction cannot be injected directly into the horizontal circuit, which is tuned for 15.75KHZ. The parabolic
correction must be gated to provide horizontal-rate pulses that can be accepted by the horizontal deflection
circuit. These correction pulses will vary in amplitude based on where they occur during the vertical parabolic
level. Two different pincushion symptoms can occur and must be observed. Is the picture stretched with pin
distortion or is it pulled in with insufficient width (black hourglass shaped sides)? Paying attention to which
symptom is present provides excellent information on where to look.
Pincushion Distortion With Excessive Width: Several scenarios can cause this with the most obvious being a
shorted pincushion amp. As most technicians check this first, other possibilities will be discussed. As mentioned
earlier, it is very important that the parabolic correction waveform be gated at horizontal rate. Check for proper
H pulse level at IC502/pin11. It should continue onto pin 8. The final check is to see if the waveform at pin 14 is
somewhat parabolic in shape (it will not be a clean one), and that it also contains horizontal component. It is also
possible that IC502 has failed and is saturating Q503. This is the most common failure in this circuit design next
to a shorted pin amp.
Pincushion with Insufficient Width: Loss of vertical parabolic correction will cause this. Check for presence at
IC502/pin 9. Check for 10VDC at IC502/pin 14. If not present, change IC502. If present, suspect open Q503,
open pincushion modulation transformer, T502 or poor solder connections.
IMPORTANT NOTE: If you have checked and/or replaced everything in the pincushion circuit and you still have
the problem, there is one more component that can cause this: The EEPROM IC004 located on the A board.
This has been found to be the source of the problem in several cases where a technician has replaced most or
all of the components in the pincushion correction circuit.
Vertical Deflection
Not much has changed in the vertical deflection design over the last few years. Looking at Figure 5-2, the RA-
3 still utilizes the traditional vertical output IC utilizing negative feedback from the deflection yoke return to
maintain linear amplification of the drive signal. It is simple and works quite well. You rarely see vertical linearity
problems with this design. As with the pincushion circuit, the vertical circuit seems to cause problems in the field
and a significant number of calls come in on the tech support line about this.
The one major change in the design on this chassis is the addition of IC1501. It provides shading correction for
the light level changes due to the angle of the outer CRTs and, functions as a “zooming” control for the vertical.
This part of the IC monitors flyback current from the ABL circuit at IC1501/pins 7 and 14 and helps to minimize
vertical size fluctuations during rapid light to dark transitions of the programming. The addition of this circuit
does not change the troubleshooting approach much, other than to add an additional path for the vertical signal.
The Y/C Jungle IC206 will output vertical drive regardless of whether output and feedback are operating properly.
This makes troubleshooting much easier than it was on circuit designs from many years ago in which the entire
vertical circuit was dependent on feedback to even oscillate.
