Power Circuit (Intellivision)
The Intellivision gets its power through the mains plug.
After that the two black 110/230V AC wires go to the transformers primary coil on the bottom.
The secondary coils out of the transformer then pass through the power switch.
The transformer inputs are on the right (blue/green/green) and the switched outputs on the left (white/blue/black).
In short, the mains power comes into the transformer directly on the primary side, the secondary coils (two of them, one is double-tapped) go through the power switch including the reference ground and come into the connector with two sets of 10V AC rails, which is smoothed by the super large capacitors to almost 8V DC, which feeds the 5V and 12V regulated inputs.
The Black/Blue rail feeds the input to the 5V regulator. The White/Yellow rail feeds the input to the 12V regulator, as well as taps off for the unregulated 16V.
There is a flying red wire that comes off the power board and directly powers the AY-3-8900 GI 8143 (STIC Standard Television Interface Chip). This red wire is the DC smoothed 5.7V off the 10VAC transformer (the same input that feeds into the 5V regulator).
This powers solely the STIC (U4) and nothing else.
The 5V regulated rail is generated by the Hitachi HA17805P LDO regulator. The input is the 10V DC smoothed signal from the 10VAC transformer input.
This is used by pretty much every single logic chip on the board.
The 12V regulated rail is generated by a MC7812CTG (or similar) LDO regulator. The input is the 20V smoothed DC from the -10VAV/+10VAC transformer inputs after bridge rectifier and DC smoothing.
This is used by the CPU (U1), System RAM (U2), and the RF Modulator.
The 16V unregulated rail is tapped off the transformers full bridge rectifier. So is essentially unregulated.
This is used by the CPU (U1) and the System RAM (U2) for the phase clock signals.
Measuring with multimeters when not loaded down this is typically showing anything up to 24V.
The -3V rail is usually between -2.2V to -3.3V. It is the negative VSS rail.
This is used by the CPU (U1), System RAM (U2) and STIC (U4) as VSS sitting just below GND pin voltage.
It is generated from the diode drops over the secondary coil and smoothed with a few capacitors.
īģŋ
