Mordaunt Short MS409W cuts out. I think due to oversensitive overtemperature sensor on the heat sink. Some of the components (two electrolitic caps and a choke) close by look to have become very hot. With...
I read about lots of similar 'cutting out' problems on other bulletin boards, revealing that this is a common problem with this particular model. Many people had the faulty speaker replaced or repaired, then had a similar problem with the new one. As the manufacturer doesn't seem to have taken any responsibility for it and as I am an Electroinic Repair Engineer, I decided that I needed to find a creative solution.
I read lots of reports about fuses blowing as the wrong rating had been fitted by the manufacturer and reports of people fitting uprated fuses (very dangerous) after the higher rated fuses had blown. People often still had the same cutting out problems after doing this. I then found a 'fix' carried out by someone who clearly had a very rudimentry grasp of electronics but nevertheless claimed to have found a cure for this problem. I decided to check out this 'fix' which consisted of adding a link between two points on the power supply circuit board. This is the circuit board covered in black heat shrink sleeve.
I examined it and found that it contained a relay that transfers the secondary voltage from the turoidal transformer to the larger, circuit board. The relay appears to be responsible for switching through the primary positive power supply voltage for everything. So, by shorting out the input to the output, the electronics is no longer dependant on the relay operating to keep the supply going to the main circuit board. I figured that it could be the relay causing the 'cutting out' problems which is why the writers 'fix' worked.
I carried out this modification to the speaker I was repairing and as far as I can see it now works perfectly. The 'fix' does of course mean that the power is never removed from the main circuit board even if it is supposed to be, say for a 'soft start' or similar. Of course, since the speaker was basically scrap as it would have been to expensive to obtain and replace the faulty parts, this repair means that my customer now has his speaker back for very little cost.
If you at FixYa would like the full details for this repair, I will only charge you a one off fee of £80 for the several hours I have spent working on this solution. Of course I am perfectly happy to make the information available free to any member of the public or non-profit organisation that would like it. After all I only really checked out the repair that someone else had posted to make sure that it was reasonably safe and that it worked. No guarantees.
Jan 29, 2010 |
Audio Players & Recorders