Hi everyone.
I have a Cambridge Audio azur 540r and face the following problem - from time to time the volume can be set only to VOL MIN and VOL MAX ( from both the volume knob and the remote ).
The volume control IC is BD3816K1 and it is controlled by the CPU M5964C40J.
The volume knob VOL_A and VOL_B signal enters the CPU and is processed to VOL_DATA and VOL_CLK which go straight to the volume control IC ( I believe the remote control signal also goes the same way ).
The CPU is powered by a stand-by transformer with constant +5V ( 7805 ).
The VOL IC is powered from the +/- 12V ( 7X12 ) rail which is converted to +/- 7.
After I replaced U2 ( 7812 ), C143 and C144. I got the following V:
U2 (7812) - IN 19.3, out 11.92
U4 (7912) - IN -20.1 out -12.11
+7 ( measured at R171 ) 6.29
-7 ( measured at R172 ) -6.64
The +/- 7V rail is little low, but still within the volume control IC limits.
I checked the rails with a DIY oscilloscope kit ( DSO138 ) and did not notice any ripples on any of the V rails ( which probably can not be really trusted ).
C139 measured around 3100uF ( should be 3300 ), but did not have at the moment something similar to replace it with ( I have stocked up now, and on the next run I'm replacing C140, C139 and C138 even for just being right next to the voltage regulator heatsink ). I'm also going to replace the C106 and C102 on the mainboard ( they are part of the +5V stand-by rail ).
And here is the interesting part - can a bad filtered power supply cause the described volume control problem? I'm not familiar with how that volume control ICs are controlled. I know that they use some kind of serial interface, but that's all.
I have a Cambridge Audio azur 540r and face the following problem - from time to time the volume can be set only to VOL MIN and VOL MAX ( from both the volume knob and the remote ).
The volume control IC is BD3816K1 and it is controlled by the CPU M5964C40J.
The volume knob VOL_A and VOL_B signal enters the CPU and is processed to VOL_DATA and VOL_CLK which go straight to the volume control IC ( I believe the remote control signal also goes the same way ).
The CPU is powered by a stand-by transformer with constant +5V ( 7805 ).
The VOL IC is powered from the +/- 12V ( 7X12 ) rail which is converted to +/- 7.
After I replaced U2 ( 7812 ), C143 and C144. I got the following V:
U2 (7812) - IN 19.3, out 11.92
U4 (7912) - IN -20.1 out -12.11
+7 ( measured at R171 ) 6.29
-7 ( measured at R172 ) -6.64
The +/- 7V rail is little low, but still within the volume control IC limits.
I checked the rails with a DIY oscilloscope kit ( DSO138 ) and did not notice any ripples on any of the V rails ( which probably can not be really trusted ).
C139 measured around 3100uF ( should be 3300 ), but did not have at the moment something similar to replace it with ( I have stocked up now, and on the next run I'm replacing C140, C139 and C138 even for just being right next to the voltage regulator heatsink ). I'm also going to replace the C106 and C102 on the mainboard ( they are part of the +5V stand-by rail ).
And here is the interesting part - can a bad filtered power supply cause the described volume control problem? I'm not familiar with how that volume control ICs are controlled. I know that they use some kind of serial interface, but that's all.
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