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Beomaster 2400-2 Bulb vs Transistor vs SAS570S Fault

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Bristol603 posted on Fri, May 6 2016 9:09 PM

I thought I would share a repair to a fault on a newly acquired BM2400-2 in case it might help someone else. The bulb for preset 3 wasn't lighting up when channel 3 was selected, although channel 3 was playing normally.The treble, bass and balance displays were also not lighting up. I purchased a bulb kit from Martin and opened up the BM to replace all the bulbs, including the one for channel 3.

i tested the old bulbs as they were removed and sure enough the ones for the treble, bass and balance were blown. However, the one for channel 3 was good and the new one that went in also did not light up. I suspected the driving transistor, but this was also good and just was not receiving the correct signal at its base to switch it on. Tracing back on the schematic then pointed at the SAS570S IC.

The IC was working correctly to select all of its channels and correctly switch on 3 out of the 4 bulbs it was responsible for, but it did not switch on bulb 3 when channel 3 was selected. I sourced a replacement SAS570S from eBay, swapped it in and that solved the problem.

I was surprised that the IC had partially failed in this way - I would have expected all or nothing and I certainly would have suspected the bulb or the transistor to be the problem rather than a partially failed IC. One lives and learns!


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EOB replied on Sat, May 28 2016 9:54 AM

Thank you for the info. I still have got mine for about 20+ years. lots of leds are not showing but somehow it still plays. Got no room for it but still cant discard it , its time it was so futuristic and still the design is an icon.

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