Mackie FAST RECOVERY M-1200, Service Manual

Page: 15 / 62

VERSIO N 1.1
SERVIC E PRO C EDURES
13
BIAS AND TEST PRO C EDURE
Afte r the unit ha s b e e n re p a ire d , the fo llo w ing sho uld b e d o ne to a ssure lo ng te rm
re lia b le o p e ra tio n. If a d isto rtio n a na lyze r is p re se nt, d isto rtio n sp e c ific a tio ns sho uld b e
ve rifie d .
1. Ad justs b ia s in b o th c ha nne ls (R1 & R51) fo r 8m V +/ - 0.3m V a t b ia s te st p o ints (J53 &
J54) a fte r unit ha s id le d fo r a fe w m inute s. With Full AC line vo lta g e a p p lie d to unit,
it w ill p ull a ro und 65W fro m the line (900m A a t 120V). Me a sure fo r DC o ffse t o n b o th
o utp ut c o nne c to rs. DC o ffse t sho uld b e le ss tha n +/ - 50m V.
2. Ap p ly a 1KHz sine w a ve to the inp uts a nd ve rify tha t the unlo a d e d o utp uts ha ve a
w a ve fo rm tha t is sym m e tric a l a nd und isto rte d . Drive the o utp uts into c lip p ing a nd
ve rify sym m e tric a l “ fla t-to p p ing ” o n the w a ve fo rm .
3. Re d uc e o utp ut le ve ls, insta ll the 0.1uF c a p a c ito r jum p e r fro m the o utp ut to g ro und
c o nne c tio ns, a nd ve rify tha t c lip p ing b e ha vio r is p ro p e r. Ve rify tha t no hig h
fre q ue nc y o sc illa tio n o c c urs ne a r a nd a t c lip p ing (p a ra sitic o sc illa tio n).
4. Re m o ve c a p a c itive lo a d ing a nd m inim ize sine o utp ut. Ve rify a nd re -a d just b ia s if
re q uire d . No te tha t the b ia s w ill no t d rift a p p re c ia b ly in a unit tha t is func tio ning
p ro p e rly.
5. C o nne c t the a m p lifie r d ire c tly to the AC line a nd c o nne c t a n 8
Ω
d um m y lo a d to
b o th c ha nne ls. Bring sine w a ve le ve l up o n b o th c ha nne ls a nd ve rify sym m e tric a l
c lip p ing . The o utp ut w ill c lip so m e w he re b e tw e e n 120V - 140V p k/ p k d e p e nd ing o n
ho w stiff the line is. C lip p ing sho uld b e a s d e sc rib e d a b o ve . Ad d the 0.1uF
c a p a c itive lo a d ing a nd ve rify c lip p ing is still w e ll b e ha ve d .
6. Ind ivid ua lly lo a d C ha nne l 1 a nd C ha nne l 2 w ith 2
Ω
. C lip p ing sho uld b e
sym m e tric a l, w e ll b e ha ve d , a nd o c c ur so m e w he re a ro und 80V - 100V p k/ p k. Ve rify
tha t c lip p ing is w e ll b e ha ve d a fte r a d d ing the 0.1uF c a p a c itive lo a d ing .
7. Re d uc e o utp ut le ve l to 20V p k/ p k a nd sho rt first c ha nne l o ne a nd the n c ha nne l
tw o . The fro nt p a ne l “ sho rt” a nd “ p ro te c t” LEDs sho uld fla sh o n the re sp e c tive
c ha nne ls.
8. Pla c e a m p lifie r in b rid g e m o d e a nd c o nne c t 4
Ω
lo a d ing to b rid g e o utp uts (a c ro ss
b o th “ +” o utp ut b ind ing p o sts). Slip so m e c a rd sto c k b e tw e e n the he a tsink-o utle ts
a nd c ha ssis sid e s. Mo nito r o ne o f the o utp uts a nd a d just fo r a 20V p k/ p k sig na l.
Sho rt a c ro ss b o th o utp uts a nd ve rify tha t a ll fo ur ‘ Sho rt” a nd “ Pro te c t” LEDs lig ht a nd
the a m p lifie r m ute s.
9. Re m o ve sho rt, m o nito r o ne o f the o utp uts, a nd a d just fo r a 60V p k/ p k sine o utp ut
(450W o f o utp ut p o w e r b rid g e d ). Afte r a fe w m inute s the fa n w ill b e g in running fa st
(he a tsink a t 60
°
C ) a nd a sho rt tim e la te r the a m p lifie r w ill m ute (he a tsink a t 80
°
C ).
The “ Ho t” a nd “ p ro te c t” LEDs w ill c o m e o n. Re m o ve c a rd sto c k a nd a fte r a fe w
m inute s the a m p lifie r w ill c o m e o ut o f m ute m o d e a nd the “ c o ld ” LED w ill re turn.
10.
Disc o nne c t lo a d ing a nd re m o ve d rive . Re c o nne c t a m p lifie r to Va ria c a nd c o nfirm
tha t the id le c o nsum p tio n is ro ug hly 65W o r 900m A, a s b e fo re . C o nne c t the
a m p lifie r to sp e a ke rs a nd ve rify tha t it so und s O K w ith m usic .