Trying to fix a Yamaha CS-15

[Gronda Andrea]

 Hello, I'm a beginner,but I would like to learn something. I'm
courrently studying the schematics of the CPB board on the Yamaha CS-15
trying to figure out how the EG1 works.... actually my target it's  to
detect why it doesn't work.
In the schematic of EG1 circuitry there are TP19,TP20,TP21,TP22; are
these  test points to check with a multimeter?
Are they to check in numerical order (es°: if every think it's ok at TP
21 the wrong component is between TP21eTP22)?
I was told that the Yamaha custom JNM4558DN is replaceble with a
Fairchild 741C
but in my ignorance I guess they have different pinouts.
Any help will be appreciated
Thanks.
Andrea
agronda-a at starnova.it

Yamaha JNM4558DN:
             ______
OUT A -|1    8|- +Vs
   -IN A -|2    7|- OUT B
  +IN A -|3    6|- -IN B
    -Vs   -|4    5|- +IN B
                ------

FAIRCHILD 741C:

                  ______
-offset nul -|1    8|- NC
         -IN A -|2    7|- +Vs
        +IN A -|3    6|- OUT
          -Vs   -|4    5|- + offset null*
                      ------

Are these schemes right?


*what does offset+/- null do?