Commodore 1901 Service Manual page 7

1} Screen Cut-Off
1) measure DC voltage at collector of TV50, TV60 and TV70
2) select the stage with the highest voltage
3) adjust screen voltage (VG2} to 170 V ± 2V
J) White Colour Adjustment
1) Set up a 40% white raster on the centre of the screen.
2) For RGBI signal level must be 4.4V to 5V at 390 termination.
3) Set PV01 (green) and PV02 (blue) to minimum position
4) Monitor wavefrom at collector at TV50 (red)
5) At intensity minimum, adjust contrast and brightness for maximum amplitude before clamping
6) Adjust PV03 (red) to have 62V ± 2V pp
7) Monitor white color temperature with detector probe head attached to the screen surface over the white
pattern
8) Adjust PV01 (green) and PV02 (blue) for white color temperature of 7500k.
K) PAL/RGBI Decode Alignment
At PAL position
1) Receive the PAL standard colour bar signal
2) Connect a jumper clip between TP and TP
3) Set the oscilloscope
to
X-Y range and connect its X probe to terminal 2 (B-Y) and its Y probe to terminal
3(R-Y)
4) Connect a jumper clip between TP2 and TP3, apply bias -^4.5 to TPI
5) Adjust CC14 slightly so that the colour becomes unlocked and the loops of the displayed Lissajoas figure
appear on the scope
6) Adjust PC01 for the absence of the loops and adjust LC05 so that each pair of lines merge together.
7) Adjust CC14 to just regain floating colour synchronization i.e. oscillator frequency = 4.433619 Mhz ± 30 Hz.
8) Trim PC01 and LCDS slightly such that all the points merge together and the absence of Venetian blinds on
the screen pattern is necessary.
adjust^
At RGBI Position
No alignment is necessary
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