McIntosh MC 22O5, Service Information

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1. U n l e s s o t h e r w i s e spec i f i e d : Resistance v a l u e s are in ohms, 1/4 w a t t , and 10% to 1 e r a n c e ;
capacitance v a l u e s sma llr than 1 a re in m i c r o f a r a d s (µF) : capacitance v a l u e s greater
than 1 are in picofarads (pF); inductors are in m i c r o h e n r i e s (µH).
2 . P r i n t e d c i r c u i t board components a re ou t1i ned on the schema t i c s by dotted l i n e s . The
c i rcled numbers on the dotted l i n e s correspond to the numbers on the PC board l a y o u t s .
3. The heavy li nes on the schema t i c s denote the pr ima ry s i g n a l p a t h .
4. The t e r m i n a l number i n g of r o t a r y s w i t c h e s is for reference o n l y .
5. A l l voltages i nd i cated on the schemat i cs a re measu red under the f o 1 1 o w i ng cond i t i ons;
a. Use of an 11 megohm impedance V T V M .
b . A l l v o l t a g e s ± 1 0 % w i t h respect t o c h a s s i s ground.
c. No s i g n a l at i n p u t t e r m i n a l s .
d. AC i n p u t at 120 v o l t s AC, 50/60Hz.
e. Front pane l con t r o l s at: R e a r p a n e l swi tches a t:
Left Gain FULLY CCW Input Level 0.75V
Meter Range WATTS Mode S tereo
R i g h t / M o n o G a i n F U L L Y CCW Power Guard N o r m a l
Speakers ON
Power ON
6. R e l a y K301 shown in e n e r g i z e d pos i t i on.
7. M e t e r a d j u s t m e n t s :
A m p l i f i e r must b e w o r k i n g p r o p e r l y t o adjust meters. O p e rate a m p l i f i e r a t f u l l power (40V rms)
i n t o 8 ohm loads w i t h 1 KHz i n p u t s i g n a l .
a. Set M E T E R R A N G E s w i t c h to WATTS.
b. Adj us t pot en t i ometer R 1 2 5 on meter board for a r e a d i n g of 200 w a t t s on the l e f t m e t e r .
c. A d j u s t R 1 2 6 for a r e a d i n g of 200 w a t t s on the r i g h t meter.
d. Set METER R A N G E s w i t c h to 0 dB
e. A d j u s t p o t e n t i ometer R 1 0 5 on meter board for a r e a d i n g of 0 on the D E C I B E L scale of the
l e f t meter.
f. A d j u s t RI06 for a r e a d i n g of 0 on the r i g h t meter.
8. Power a m p l i f i e r b i a s adjustment:
Operate M C 2205 a t 1 2 0 v o l t s l i n e i n p u t w i t h n o i n p u t s i g n a l . Measure t h e i n p u t power
( a p p r o x i m a t e l y 50 watts) or current ( a p p r o x i m a t e l y O.4 amps). The b i a s p o t e n t i o m e t e r s R241 &
R242 are located on the power o u t p u t PC boards.
a. Turn both b i a s potentiometers f u l l ccw
b. Rotate b i a s ad jus tment cw to the p o i n t where the l i n e i n p u t power or current b e g i n s to
i ncrease then back off s l i g h t l y to the p o i n t where the l i n e in put reaches its l owest
va l ue .
c . Repeat step b for each channel i n d e p e n d e n t l y .
S C H E M A T I C N O T E S
M C 2 2 0 5