Bang & Olufsen Type 2651 Service Manual page 65

7
5 - g
REPAIR TIPS, ENGLISH
Bang &Olufsen
Load the CD (LOAD).
- Press 46.
CD starts playing from lead in (display = 0). No sound is
produced by the speakers.
- Press 47.
CD brakes and stops playing.
- Press CD.
- Press 48.
CD winds towards the extreme outside position and stops
there.
- Press 49.
CD winds towards the centre and stops there.
Test mode is abandoned by pressing . or disconnecting the mains voltage.
The laser, the laser supply in 81c7800 and the monitor diode form a feed-
back system. A defect in the laser supply may result in destruction of the
laser.
As it is impossible to check and repair a feed-back if one part of the system is
missing, the laser supply can be checked by means of the below circuit.
The green LED replaces the laser. The voltage across the l8ohm resistor is the
feed-back voltage for the monitor. The 33ohm resistor and the switch make
it possible to change the power consumption from the laser supply.
T O L O 8 P t 8 0 t - 6
T 0 L M 8 P t 8 0 t - 7
l ^ ^ . ^ ^ .
t u J d P t d u t - 3
Green LED, e.g. CQY94, part no. 8330054.
Remove the flex PCB from Pl801 on the pCB8.
Connect the above-mentioned circuit to pl801 on the pCBg.
Connect Sl (pin 6 of 81C7800) to ground.
when st (stan Initialization) low, the laser supply can be switched on in
TESTMODE. Then press CD and 40.
M e a s u re th e L O vo l ta g e o n p i n 6 o f 8 P 1 8 0 1 .
5 1 o p e n :
L O f ro m 1 .8 V to 2 . 3 V
LM from 170 mV to 220 mV
T h e g re e n L E D e m i t s li t t le l i g h t
S'l closed:
L O f ro m 1 .8 V t o 2 .3 V
LM from '170 mV to 220 mV
T h e g re e n L E D e m i t s l i t tl e l i g h t
D u rin g t h e ch a n g e fr o m 5 1 c l o s e d to 5 1 o p e n , t h e L E D w i l l s h o r t l y e m i t m o r e
light than usual. The feed-back system ensures that the same amount of
current passes through the LED irrespective of whether S1 is open or closed.
( l
Checking the laser supply
/I
l
! . o N r r . r . , D T R E C T L y
I
t r r H E s E R v O P C B 8
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