Technical Service Bulletin SN3-006
Chroma Analog & Autotune
April 4, 1983
Calculations indicate that the Auto-Tune functions operate closer to center range when the +5 volt analog supply is adjusted slightly on the high side. The analog +5V is the reference voltage for the D/A converters.
Set the +5 volt analog supply between +5.04 and +5.06 VDC with a digital voltmeter. This can be measured from JI pin 4, the yellow wire at the supply to chassis ground, a green ground strap. Potentiometer R22 on the supply controls the analog +5 volts. After setting the analog +5V check the offset null between TPO and TPI on the I/O Board and adjust potentiometer RI for 0.000 volts. Also check the 50% duty cycle of the oscillators and adjust the trim pots and necessary.
Rhodes Chroma National Service Manager