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5. RA-3/3A Deflection Circuits
Check for V drive out of pins 34 and 35 of the Y/C Jungle IC206. Since this unit shuts down during a vertical
failure, you will have to override by shorting the main relay.
Unplug all three CRT sockets when doing this.
It
is obvious why this unit shuts down during a vertical failure. If IC206 does not output vertical sawtooth signals
from the + and – drives at pins 34 and 35, it is likely at fault. If they are present, continue down the line and make
sure they are getting through the zoom IC1501 and into pins 1 and 7 of vertical output IC1509. Check the +15V
and –15V supply rails. If present, you are left with a bad driver IC, open yoke or open connection to the yoke.
Repeat Vertical Output IC Failure
:
If IC1509 fails immediately upon replacement or soon thereafter; it is usually
the fault of C1557. This is the boost capacitor. It charges to almost 30VDC during the lower half of the vertical
sweep to provide additional voltage to allow the beam to retrace to the top rapidly. When this filter dries out or
opens, the output IC will attempt to accomplish the retrace but the negative feedback line will resist the sudden
voltage kickback from the yoke and the –15V drive will cause the IC to draw excessive current. In smaller
televisions, a boost capacitor failure causes slight loss of vertical at the top with some fold-over.
Insufficient Vertical Height
:
The vertical output IC is receiving improper drive levels or it is unable amplify properly.
Due to the nature of the operational amp within IC1509, it is rare for this IC to be the cause. Operational
amplifiers have massive amounts of gain, which is why they need negative feedback to keep them under control.
Gain problems are most likely to be caused by improper supply voltage (very rare) or problems in the feedback
line. The feedback line should always be checked with an oscilloscope when height or linearity problems arise.
In this chassis, the best point is the top end of the ground return resistors (R1549 and 1552). What should
normally be here is approximately 1VPP of vertical rate sawtooth. If there is a problem here, you will observe one
of two things: A significantly larger sawtooth level or horizontal frequency contamination in the sawtooth. A large
sawtooth indicates one or more of the ground return resistors, or the thermal compensator TH1501, has opened.
The negative feedback of the op amp will respond by reducing gain. If there is a large amount of horizontal
component in the feedback, the amp will also reduce gain since the average DC level will be higher at this
frequency. The vertical deflection yoke windings are right next to the horizontal windings so it is very easy to
induce this into the vertical return. Suspect an open C1552 at this point.
Should the feedback line check OK, you now have a possible input problem. The YC/Jungle can cause this and
it is difficult to verify without replacing it. Before changing this expensive, multiple-pin IC, try one more thing. The
main NVM IC can cause this problem even though it is capable of changing the height in the service mode. Try
changing the NVM first. It is less expensive and only has eight legs.
