From page 2 of "1802/1804 Full BASIC Math/ROM board - Assembly Instructions"

mods to the Giant Board for Full BASIC board operations. Commentary by Herb
Johnson in []'s, last updated May 25 2025.

Make the following connections from the 86 pin socket reserved for the Giant
Board and the 86 socket to be reserved for the math/ROM board.

( ) 1. Connect-8V DC to pin 15 on math/ROM 86 pin socket.
[-8V needed for operation of 57109 chip]

( ) 2. Connect pin 51 of Giant Board socket to pin 51 of math/ROM socket.
[I/O instruction 65H OUT 5 operates data in 1852 latch to 57109 chip]

( ) 3. Connect pin 79 of Giant Board socket to pin 79 of math/ROM socket.
[I/O instruction 6AH IN 2 operates data out 1852 latch from 57109 chip]

Make the following revisions to your Giant Board.

NOTE: The two diodes and the capacitor are installed on the circuit [traces] side of the
board. 

( ) 1. On circuit side of the Giant Board cut the foil between pin 70 of the
86 pin edge connector and the junction of Rl9 (1 meg) and pin 4 of Al2
(LM 3900) (cut the foil near the junction Rl9 and pin 4 Al2)
[This breaks the cassette input circuit op-amp output to pin 70 for /EF2.]

( ) 2. Solder a diode (IN4148) between pins 16 and 1 of A6 (4049) with the
black band toward pin 1. [Pin 1 is +5, pin 16 has no connection. So it's
a convenient junction.]

( ) 3. Solder a diode (IN4148) between pin 16 of A6 and the plated through
hole located between pins 4 and 5 of A6 (4049) with the black band
toward pin 16 of A6. [Pin 16 is that junction. The hole connects to buss
pin 70, /EF2.]

( ) 4. Solder a .luf capacitor between pin 16 of A6 and the junction of Rl9 (1 meg)
and pin 4 of Al2. [A12 is the op amp for cassette input, pin 4 is the op amp output.]

[The net effect of these mods, are to install diodes on the A19 op amp that reads 
cassette input for LOAD. They are on the output side of the op-amp to /EF3. They
add a coupling capacitor that blocks DC from the op amp output. The pair of diodes
adjusts and limits the voltage of the signal going to /EF2 on the 1802 processor. - Herb]