Hi All,

For the second time since I've had my mixer, the power supply board has failed. The first time I was setting up for a show and the board failed on power up (lights flickered, then nothing - had to run back home and sub out for my 16-channel analog Mackie). I sent it back to PreSonus for a warranty repair. Got it back and it worked for a couple years. Then I went down into my studio one day and it was dead again. This time (since it was out-of-warranty) I purchased a replacement PS board through Full Compass and replaced it myself. The board powered up and seems to be functioning (haven't stumbled into an issue yet, passes audio, no rude noises, computer talks to it...).

So now I have the supply I removed. There is clearly a burnt diode, and the small electrolytic cap nearby seems to have its top bulging a bit. There is also a tiny chip thing next to the diode that looks dicey, but it may be that the diode may have bled out onto it, rather than that part also being damaged (not sure how to tell). But I thought that maybe if I replaced the diode and cap I would have a spare in case it happens again.

Does anyone know of a diagram for the PS board somewhere (where I could determine what diode to order)? Or maybe someone might know a part number for the diode (too burnt to read). I can probably identify the cap from the markings.

A further concern stems from comparing the new one and the old one. In this case the "old" one is a replacement (or a repair, I suppose) of the original, since that was done under warranty at the Presonus facility in Louisiana. The "new" one is from Full Compass. The area of interest for this concern is near where it appears that the AC connects. There are a couple of traces there that allow for a soldered in fuse and apparently an MOV type of surge protection. On the "new" board those are populated with a 2-amp slow blow fuse and a blue disk MOV. The board is stenciled with 2A for the fuse. The "old" one has no fuse and no MOV, and instead has a jumper wire, essentially in place of the on-board fuse. The stenciling on the old one indicates 3-amp slow blow. Otherwise, from my inspection at least, the boards look identical.

So, any insights as to why there was no protection (fuse, MOV) on the PS that was removed, and why the screening is showing different fuse values (2 or 3 amp)? I suppose the jumper probably takes rather more current before it blows (apparently the diode became the fuse). I just wonder if the PS might vary from maybe a 16 channel compared to the 24 channel board or such? Since it was that way (without fuse/MOV) as it came back from PreSonus after repair/replacement of the original supply, I assume they did that with intention, either because even the 3-amp fuse wasn't enough, or because they decided it wasn't needed (or didn't want a repeat problem?).

Any insights or thoughts would be appreciated!