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I'm working on a BeoSound 4 with some odd symptoms:
1 volt differential is not a fault, check P102 pin 4 MAINS_FAIL should be around 5V
I dont see in that measures that something is wrong with powersupply, why do you??
i think it’s processormodule and that only authorized servicepartners that can fix for you
Thank you to each of you for your thoughts thus far.
To explain: When I began life in electronics servicing, I was taught to always start with the PSU and ensure it's spot on. On an unregulated PSU, I wouldn't worry about a 12V line being at 13V, but from a regulated PSU it indicates a failure. Given a schematic, I could verify this. Some high-tech equipment checks voltages are within certain bounds, and if not, will shut down - such a function could explain the symptoms I'm seeing.
The MAINS_FAIL and POWER_ON lines each sit at 4.9V. SMPS_Sync sits at 0.008V, but according to the manual this line is unused. The +12V output is actually +12.82V, whilst +5V, +6V and -12V are well-neigh spot-on.
However I take it from your comments that I should stop worrying about the +12V.
The fact that the glass works as intended, and the LOAD button works implies that the CPU is working correctly. The next step should therefore be to find out why there's no display. It has both supply voltages, so either it's not receiving data, or the display is faulty.
Some hi-tech displays have a built-in self test, independent of the host processor. Can anyone tell me whether this display has such a test (and how to enable it) or is my only way forward to monitor the data lines to see whether they are active and/or find a known-good display to try?
Mark
Use the oscilloscope, check on P1 (Display 10) the signals DISP_CLK, DISP_SO, DISP SI and then the signals on the display.