G08 Vector Monitor Guide
Page 7 of 41
Issue 5 deflection boards have places for resistors R636, R637, R736, R737 screened on top of the
board. Issue 5 deflection boards may be found with or without diodes D601, D602, D701, and
D702 populated. If your deflection board has these diodes, just leave them installed. They do not
appear to make a functional difference.
There are even different issue numbers for the foil patterns screened on the bottom of the deflection
boards. These issue numbers on the bottom of the deflection boards do not necessarily match the
issue number on the top of the board. For example, you might find an issue 2 screen on a issue 3
deflection board, or issue 4 screen on an issue 5 deflection board.
All these different variations make it very difficult to write a document for a very specific
deflection board. While one deflection PCB may look much different than another physically, most
of the time one will find the components mounted or soldered somewhere else which makes the
two boards functionally equivalent.
The schematics found in the Tac/Scan and Star Trek manuals matches the schematics found in the
“Preliminary service data for the G08-003/004 X-Y color monitor (up to date as of Feb 1982)”.
Neither the schematics nor the parts list show diodes D601, D602, D701, or D702. For the most
part, it appears that all issues of the G08-003 deflection board are attempts to hack (and probably
should be hacked) to support the G08-003/004 schematics in general.
I would not recommend modifying any G08 deflection board from issue to issue, but to simply
verify that the current hacks on the board match the schematics in the Tac/Scan or Star Trek
manuals. If they do not, modify the deflection board accordingly.
The input amplifier, IC600, and surrounding circuitry on the deflection board serve two purposes:
First, it compensates for a type of distortion known as the pincushion effect. This occurs because
the electron-beam must travel a greater distance when striking the edges of the CRT than when it
hits the center. If we cause the beam to trace along the edges of the CRT, the beam would draw a
box with its left and right sides bowed inward. To compensate for the effect, this circuit offsets the
point where the beam would normally strike the CRT surface.
Secondly, this circuit contains two error amplifiers, one for the horizontal and one for the vertical
inputs. Each error amp has two inputs; one is set to zero volts, the other accepts the analog signal
from the G-80 system, sensing current movement in the deflection coil. The analog signal is
allowed to pass through the error amps and drive the deflection (power) amps. The outputs of the
“X” and “Y” power amps pass current through their respective deflection coils. The output leads of
the two coils are connected back to the analog inputs of the respective error amps, as mentioned
above. This acts as an error, or feedback, signal and ensures that the current through the deflection
coil remains proportional to the voltage on the error amp inputs. If this signal were not provided,
there would be a slight deflection error when an analog input signal was present.
IC600 is a custom chip, Electrohome part number 14-002156-01 (and Sega part number 315-0117).
This IC can be destroyed in certain failure modes, and since it is custom, the only way to repair a
deflection board that has a bad or missing chip is to find another deflection board.