Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0

Page 9 of 53

Deflection Amplifier

The deflection amplifier converts the pick off voltages from the size pot (R109) into a current that

drives the deflection yoke winding. The input is a differential stage consisting of transistors Q101,

Q103 and Q102. Q101 is an emitter coupled with Q103 to provide a degenerative feedback loop

from the yoke. Q102 is a reference current source to both emitters and a fixed amount of current

always flows through it. If this current varies, the picture will be offset from center. Too much

offset will cause the circuit breakers to blow.

This reference current is determined by the voltage drop across R113. Diodes D105 and D106

determine this drop. The voltage across one of the diodes is cancelled by the base-emitted voltage

of Q102. R113 should constantly read 0.6 volts DC. This means a constant flow of about 3mA

through Q102.

This 3mA bias must come from the emitters of Q102 and Q103. Excess current is picked off at the

collector of Q101 and feeds pre-driver Q104. The reference current source for pre-driver Q104 is

Q105, D107, D108 and R116. Bias current through R116 is about 0.22mA.

At this point, the deflection circuit can again be divided into two identical circuits. One circuit,

which controls the lower half of the screen, is comprised of Q104, Q106, Q108 and Q110. The

other circuit, which controls the upper half of the screen, is comprised of Q105, Q107, Q109 and

Q111.

Q104, Q108 and Q110 are three stages of amplification, while Q106 is used as current limiting

protection for Q108 and Q110. The same holds true for the other configuration of Q105, Q107,

Q109 and Q111.

Current is delivered to the yoke in a push-pull manner by transistor pairs Q108 and Q110 for

positive current translations. Q110 and Q111 are power driver transistors mounted on the

humongous heatsinks on the left side of the monitor frame.

Diodes D109, D110 and D111 set up a crossover voltage threshold to prevent both halves of the

push-pull output from turning on at the same time. Should one of the diodes open, only half of a

display will be generated. Should the diodes become resistive, both power transistors will turn on

simultaneously and generate excessive heat.

If more than 3 amps are drawn through sense resistors R120 and R121, transistors Q106 and Q107

turn on and shut off the power driver by sinking the base current to drivers Q108 and Q109. This

protects the hardware against further damage.

R124 through R129 are used as a current divider network for the yoke. R122, R123, and C102 form

a R/C network, which compensates for any counter EMF that may develop by the expanding and

collapsing of the deflection coil's electromagnetic field. Revision B and later monitors do not

In the horizontal section of the deflection amplifier, Q205, Q207, Q209 and Q210 control the left hand side of the

screen, and Q204, Q206, Q208 and Q211 control the right hand side of the screen. By dividing the screen in this

manner, four quadrants of deflection area have been developed.