Mackie FAST RECOVERY M-1200, Service Manual

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M•1200/M•1400 SERVIC E MANUAL
C IRC UIT THEO RY
10
THERMAL MANAG EMENT
Re fe r to sc he m a tic o n p a g e 29.
The M•1200/ M•1400 T-De sig n He a tsink/ Fa n c o o ls o utp ut d e vic e s e ve nly a nd d o e s no t
c o lle c t d ust o n the c irc uitry. The fa n o p e ra te s a t tw o sp e e d s, c o ntro lle d b y the
a m p lifie r. An LM35DZ m o unte d in the c e nte r o f the he a tsink p ro vid e s te m p e ra ture
info rm a tio n to the fa n c o ntro l a nd o ve rte m p c irc uits. The re is a lso a the rm a l b re a ke r in
the p o w e r tra nsfo rm e r.
FAN C O NTRO L C IRC UIT
The fa n vo lta g e c o m e s fro m a fe e d b a c k re g ula to r c irc uit fo rm e d b y Q 91 a nd Q 92. The
o utp ut vo lta g e is p ro g ra m m e d b y the ra tio o f R209 to R211/ / R207 (/ / =p a ra lle l). Whe n
the unit is p o w e re d up C 83 c ha rg e s thro ug h R241 p ro vid ing a 40 se c o nd d e la y b e fo re
the fa n sta rts. As C 83 c ha rg e s, U6D’ s o utp ut switc he s to -16V, sta rting the fa n. The n
U6A’ s o utp ut sw itc he s to o p e n, a llo w ing U6B to inc re a se the fa n sp e e d , if trig g e re d . R240
a nd C 82 g ive the fa n e xtra vo lta g e w he n sta rting .
The fa n sp e e d is inc re a se d b y U6B a d d ing R211 in p a ra lle l w ith R207. (Q 91 w a nts it’ s
b a se a d io d e d ro p a b o ve g ro und , so Q 92 d o ub le s its Em itte r vo lta g e ). U6B is trig g e re d
b y U4D to inc re a se fa n sp e e d if;
•
C ha nne l 1 SO A p ro te c tio n is a c tiva te d (U5C ), O R
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C ha nne l 2 SO A p ro te c tio n is a c tiva te d (U5D), O R
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The he a tsink is a b o ve 60 d e g C (U5B) AND p ro g ra m is d e te c te d (U4C ), O R
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The he a tsink te m p e ra ture is a b o ve 80 d e g C (U5A).
U6C a nd Q 89 a re use d to re se t the c irc uit o n p o w e r d o w n. Und e r no rm a l o p e ra tio n
C 50 is c ha rg e d via D57, Ho ld ing Q 89 o ff. Whe n p o w e r is re m o ve d C 50 d isc ha rg e s a nd
Q 89 switc he s o n a s the ra ils c o lla p se . Whe n the vo lta g e o n Q 89’ s c o lle c to r fa lls b e lo w
g ro und U6 sw itc he s to the ne g a tive ra il d isc ha rg ing C 82 a nd C 83.
THERMAL SHUTDO WN
Extre m e he a tsink o r tra nsfo rm e r c o re te m p e ra ture w ill a c tiva te O VERTEMP. U5A
a c tiva te s o ve rte m p if the LM35DZ d e te c ts he a tsink te m p e ra ture a b o ve 80 d e g C .
Fe e d b a c k re sisto r R137 re sc a le s U5A’ s vo lta g e re fe re nc e so tha t the he a tsink m ust c o o l
to b e lo w 50 d e g C b e fo re o ve rte m p is d e a c tiva te d . O ve rte m p c a n a lso b e a c tiva te d
b y the p o w e r tra nsfo rm e r the rm a l b re a ke r (via Q 89). In e ithe r c a se , b o th c ha nne l a re
m ute d via D69 a nd D66.