Super manual it contains all the things you need to service your Marantz 2100.
Text excerpt from page 8 (click to view)
AV-21P8
s CENTER ADJUSTMENT (Page 25)
[SUB MENU 6. CENTER] Setting item TREBLE BASS (Do not adjust.) (Do not adjust.) : Do not adjust. Initial setting value (fixed) +2 +3
VICTOR COMPANY OF JAPAN, LIMITED TELEVISION RECEIVER DIVISION 1106 Heta, Iwai-city, Ibaraki-prefecture, 306-0698, Japan AV21P8BK-BK #3 CTH 0009 CRT