Video signal adjustments
The VIC-20 can be attached directly to a composite colour monitor or a television that has audio/video inputs by using a DIN to multiple RCA-connector cable. This results in a much clearer picture than when the RF modulator is used. However, when first connected this way the video can appear "off". White may show as grey, shadows may appear around characters and black may look wrong.
This can of course be compensated for by adjusting the controls on the monitor, but such a solution forces the monitor to be adjusted far off its default settings. A better solution is to make adjustments to the VIC-20's video output by tweaking the potentiometers inside the VIC's video section (on the motherboard).
On the original VIC-1001 and extremely early VIC-20s (ones with PET style keyboards and motherboards with no metal RF shield around the video section) there is only one potentiometer to adjust (as shown below). Note: this has not been tested so try at your own discretion.
Later VIC-20s have a metal, box-like RF shield around the video section. The lid of this can be popped off to expose the VIC chip and potentiometers (in fact, it's a good idea to leave this lid off permanently to keep the VIC chip cool).
Most VIC-20s with two-prong power supply connectors on the right side will also have a pair of potentiometers located right above the VIC chip (MOS 6560) on the motherboard.
On these VIC-20s the potentiometer at location R7 controls the strength of the video signal. The potentiometer at location R32 adjusts the black level (sets the forward bias on common emitter buffer/amplifier Q7). On a VIC-20 with a DIN type power connector (cost reduced motherboard), the potentiometer controlling the video level is located at R10. The extra pot is not present on cost reduced model and was likely replaced with fixed value resistor.
The device labelled as C55 (or C48 for cost reduced board) is a fine tuning adjustment for the TTL clock driving the 6560 chip and should not be altered.
Before adjusting any potentiometers inside the VIC-20 make sure to mark the original positions so that you can return them to their default states if need be.
VIC-20s adjusted this way may not look right when connected to a video display through the RF-modulator.
The VIC-20 video output is composite, doubled on two pins with a different resistance (at least on some models). Internally, the VIC chip seems to have output for luma and chroma, but it gets mixed before the output. This means that two pins of the VIC-20's DIN type video connector carry almost redundant signals (only one need be used).