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c) Replacement of components.
c1) to replace any component from pcb, with the exception of fuses B1 and B2,
the pcb must be detached from the main metal plate.
This requires:
- removal of terminal J12,
- removal of M3 screw used to secure the LM4700 circuit to the heat sink,
- unsoldering of cables connecting pcb with the input terminal,
- removal of the potentiometer knob,
- removal of potentiometer securing nuts,
- removal of two M3 screws securing pcb to main board (see dia.1),
- removal of pcb, with particular care not to lose the mounting spacers,
now all the components are accessible for replacement,
- assembly back in the reverse order
Note:
When replacing LM4700 ensure to apply the heat conductive compound onto the
heat sink conductive surface and that both surfaces are aligned and in good contact.
c2) Replacement of components housed on the main board i.e. mains switch,
mains lead, fuse holder, input terminal
- after replacement seal using silicon compound.
3. Typical faults and corrections.
No.
Fault
no sound - LED not lit
1
no sound - LED shows red
2
no sound - LED shows green
3
correct sound - LED not lit
4
Cause
faulty fuse B3
or faulty mains cable
faulty fuse B3 or B2,
or faulty transformer Tr2,
or faulty LM4700 unit
faulty speaker
no signal at signal input
defective signal channel
faulty indicator circuit B4,
U11, T2, C35
Correction
replace B3,
replace mains cable
replace B3 or/and B2,
replace transformer Tr2,
replace LM4700 unit
replace speaker
check amplifier to signal source
connection
check for signal at amplifier
n10 U1 input
replace faulty part
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