Infinity Infinitesimal IV, Service Manual

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TROUBLESHOOTING
the RS/SSW-I0/INFINITESIMAL IV SUBWOOFER Amplifer
We are assuming at this point the unit has been tested and there is either distortion, no output,
"breathing" from woofer, it blows fuses instantly, etc. If the problem is no output whatsoever and the
woofer does not react at all upon hearing the relay close, disconnect and check the DCR of the
woofer with a DMM; it should be 1.7 -2.2
Ω
(to rule out a defective woofer). Another simple external
problem that can be responsible for little or no output is: using the high level input terminals and
having one polarity reversed on either input cable — (the right and left signal will effectively
cancel at
the subwoofer input.) The relay should close (an audible "click") 2 - 5 seconds after turning on the
unit. And obviously if no "click" is heard the relay has not closed and there will be no output.
However whether the relay closes or not is of no consequence in the early stages of
troubleshooting once the unit has been found defective. 99% of the time the relay itself is not
defective.
FOR ALL PROBLEMS (EXCEPT BLOWING FUSES, SEE SECTION IV):
After amplifier removal from cabinet, pull back plastic cover (NOTE: plastic amp cover not present on
early RS Subwoofer models) and examine PC-1 (main circuit board). It is usually not necessary to
completely detach the amp cover from the amp assembly.
I
RELAY IS CLOSING NORMALLY (Audible "click" is heard 1 - 5 seconds after power is turned
on):
A.
R2 & R3, 430
Ω
1watt resistors are burnt up or discolored: problem is most likely
defective ICI and IC2 on PC-2 (the small input board) OR one or both of the zener diodes in
the power supply.
B. To check, replace R2 & R3, power up unit and check DC voltages across R2 & R3; it
should be ± 11-14 VDC.
If voltage is higher, remove socketed ICI and IC2 (LF347N &
LF353N) on PC-2 (the small input board) or unsolder 5 - conductor ribbon attaching PC-1 to
PC-2. If no change in voltage, on R2 replace ZDI, on R3 replace ZD2.
If voltage is normal
OR drops to normal after IC removal/unsoldering ribbon, replace ICI and IC2 on PC-2
(the small input board). If the IC's are in sockets (the latest model) it will be easy; if not the two
IC's must be desoldered and removed without damaging the rest of the board. IC sockets are
recommended for the new IC's.
Or replace PC-2 in its entirety. (Infinity part# A021-5158)
C.
R2 & R3 look normal: follow instructions "B" above concerning DC voltage across R2 &
R3. If all voltages are normal, replace ICI and IC2 (LF347N & LF353N) on PC-2 (the small
input board A021-5158).
NOTE
: If PC-1 board is badly burnt because of R2 & R3 it is considered contaminated and
should be replaced in its entirety. (Infinity part# A021-5152)
II
RELAY IS NOT CLOSING
A. Follow complete instructions "B" above (RELAY IS CLOSING NORMALLY) concerning DC
voltages across R2 & R3. A short in ICI, IC2, or IC3 will prevent the relay from closing.
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