More Drumbrute ...

All back together and working ... 

Arturia DrumBrute ...

 So, I was attempting to repair a bit of music electronics yesterday evening. Fault in the power supply somewhere - one of those overload ones, where you turn it on, the lights flash briefly and then all quiet. I hooked it up to a power supply with a current meter, found it was sucking a few amps before dying. 

There's a resettable fuse on the input, which goes open circuit when it fails. 

Aha, I thought. I can tell what is shorting out, since whatever it is will get hot quickly, and then cool down. Having worked my way round the power supply, looking at likely culprits (is that cap a bit bulgy, shall we lever it off the board and retry?) .. I thought I would test the first voltage regulator. It's a tiny thing, (a TPS5431) brings the supply down to 5V pre-regulated before going off to a 3.3v reg, to a switcher which feeds +12 and -12 etc. 

Turned on again, with finger applied. Now that got stupidly hot, very very quickly. And behold, it is showing a resistance of about 7 ohms to ground on the output of the regulator. Trouble is, I couldn't tell if it was the voltage reg or the schottky diode (SS16) next door that suddenly got so very hot. So, I am now looking at the blister on my finger to decide if it is 8mm x 6mm or 6mm by 4mm burn.

Well, the diode is easy to lever one end off the board and have another measure. Ah, it's not the diode. So must be the voltage regulator itself which has gone deady-byes. I hope that whatever happened to the 5V during the time of failure hasn't done too much damage (the 3.3v was still regulating just fine as were the 12v ones).  

I should have been more circumspect and noticed that the voltage reg was showing signs of a little patch on its surface where it has become extremely hot. I will need to lever that off the board now, and substitute in a small external regulator to see if the beast comes up or not. If it does, I might just leave it with a replacement voltage reg on a small board.