Can anybody identify this SMD diode?

[777funk]

There are two diodes here and one was reading a voltage drop of 0.005V both ways. So it's no good.

But the problem is, I can't identify it since it's SMD and I'm not at all familiar with SMD diode markings. The good one measures somewhere around 0.2V forward voltage and of course OL in reverse.

I'm pretty sure (not 100%) this is in the 48V phantom power supply.

Probably not smart of me to have made an uneducated guess, but I tried a 1N4007 in this spot and it burned up pretty quick. Maybe the diode was wrong (of course it was, going by the forward voltage drop) or maybe that whatever killed the original diode is still dangerous to the new unit.

Open to any guesses at what the diode could be and thanks in advance!!

EDIT: Maybe Shottky?? EDIT again... I feel pretty dumb in this case. A silicon diode can't handle the fast switching frequency of the boost converter most likely feeding this thing. So it must be a shottky. Assuming that this is the phantom power circuit that this is a part of (unfortunately, I have no schematic).

 

[Khron]

I'm pretty sure (not 100%) this is in the 48V phantom power supply.

Haven't bothered looking through my teardown of a Profire 2626, i guess? Or even followed (with the continuity tester on your meter) where that supply rail ends up? Test points for all the supply rails are pretty clearly marked, if memory serves.

I feel pretty dumb in this case. A silicon diode can't handle the fast switching frequency of the boost converter most likely feeding this thing. So it must be a shottky. Assuming that this is the phantom power circuit that this is a part of

Well, ultrafast diodes are also "silicon", without being Schottky, so...

 

[777funk]

I have checked voltages and the unit works (minus the blown out diode), but no phantom power. I don't think your teardown shows much detail on the phantom power end of things.

I just measured at TP940 for phantom (board is marked 52V at this test point) and it measures 18V which is what I'm getting at the diode below the missing burned out diode. So I do believe those two diodes I pictured are part of the Phantom supply. No idea how it works other than I'd think it has to be a boost converter. I think I have some Schottky diodes but no idea what voltage and current rating this would need to be. Condenser mics use a max of 10mA and there are 8 inputs so I'd guess around 100mA min would be good and phantom is 50V approx so maybe a 60V rated diode.

 

[Khron]

No idea how it works other than I'd think it has to be a boost converter.

No need, probably just an extra winding on that flyback transformer.

I can't identify it since it's SMD and I'm not at all familiar with SMD diode markings.

Fortunately we have Google nowadays...

https://www.s-manuals.com/smd/sf

Going by the package, it's most likely the SS0540 - 500mA 40V Schottky, but I'm reasonably sure they're both in series (otherwise they would be severely underrated). Any similarly (or higher) rated Schottkys should do, though.

I just measured at TP940 for phantom (board is marked 52V at this test point) and it measures 18V which is what I'm getting at the diode below the missing burned out diode.

Might it though be some voltage doubler arrangement, including those green electrolytics, though? That might explain SOME voltage making it through...

 

[777funk]

You may be right. Maybe a doubler. Not sure.

I took apart another dead interface and looked at what I'd assume was the phantom section on that one and grabbed a diode that had a number that was possible to look up (interestingly the number on the one in the M-Audio didn't seem to turn anything up for me). But I pulled a diode in an old failed Presonus (cap exploded and ruined the PCB) marked SR26 which is a 2A 60V Schottky in a larger format. And... it's alive! Getting phantom at the test point now.

 

[Khron]

60v's a bit on the edge, but oh well...

 

[777funk]

60v's a bit on the edge, but oh well...

Yes I suppose it is.

This purchase was by far not a good deal! Live and learn. I thought to myself, I'd like another 2626 (remorse for selling my old one) to go with my 610. I bought this for $25 plus shipping in needing repair condition.

-Fixed the SMD MOSFET which was shorting the supply (didn't know FETs came in SOIC-8, so I didn't check it initially). That took a while. I figured the short was a bad cap.

-Next Phantom was not working. Found the shorted Schottky. Replaced with a 1N4007 rectifier diode (all I had). Did not work. Too slow I'm guessing. Dug through my junk pile and found a real Schottky in another broken piece of gear. Problem solved.

-Next. Noticed headphones (both) were a little low on output. Noticed that if I touched an LC459C chip near the headphones area of the board, the volume would go up to normal level for a second then fade back to low. It was sort of like when you forget to put a 1M drain resistor on the grid of a preamp tube and the plate becomes charged. I took the board back out and looked for bad connections. None. Finally I measured the "Main Out" pot which feeds the audio in on the LC chip (A/D). It should be 10k across pins of the pot, but measured OL. The control wasn't working, but I wasn't sure that it wasn't disabled in software (possible to do-gives full volume out always). But no, after measuring, it was obvious that the pot had an issue. I pulled it out and turns out that the pins were broken off sheared. This thing must have been dropped hard and overvoltaged. Whoever I bought it from was very hard on their gear!

-Last (and not going to be fixed this go-round). Channel 7 mic in doesn't work if phantom is on. I'm guessing a blocking cap has failed shorted and is putting DC on the THAT preamp chip. Didn't check. EDIT: I found two lost screws from the inside and decided to tear it apart again today. I pulled the input electrolytics out from the top exposing the leads (insides of the cap). I replaced those and now CH7 works when phantom is on. I replaced the 47uF with 1uF film caps. It sounds pretty close to as fat as the 47uF with a condenser on voice. Of course voice can't get down to 20 Hz.

So all said and done, this time it was not worth the cost savings ($50 more could buy a good unit). Always a gamble on broken gear. I tend to buy it because a lot of the time, the seller just didn't know how to test without the power supply or something else user error. But now I know more about the 2626. And at least it works.

 

[Cqwet Dbdfte]

If the parts broke, they may be under designed. Replace with higher voltage, higher current rated parts. If you have space, use higher voltage caps, etc.
If a 40V (fast) diode broke, replace with the highest voltage available that will fit.
Maybe https://www.digikey.com/en/products/detail/genesic-semiconductor/GB01SLT06-214/3904841

 

[Khron]

Maybe https://www.digikey.com/en/products/detail/genesic-semiconductor/GB01SLT06-214/3904841

$1.63 for ONE diode? Come on, man... 1A 650V silicon-carbide, for a phantom power supply, really? Not to mention the considerably larger SMB package...

Some more realistic choices (in stock, 60-100V Schottkys, in ascending price order):

https://www.digikey.com/en/products...zTPpUBsNsIUbH4QLUAEwVOgogZeVLOWQBPaXbSpuRdXSA

 

[Cqwet Dbdfte]

$1.63 for ONE diode? Come on, man... 1A 650V silicon-carbide, for a phantom power supply, really? Not to mention the considerably larger SMB package...

Some more realistic choices (in stock, 60-100V Schottkys, in ascending price order):

https://www.digikey.com/en/products...zTPpUBsNsIUbH4QLUAEwVOgogZeVLOWQBPaXbSpuRdXSA

Didn't see the package size, pretty big for 1A. SiC diodes are a novelty, Who cares about price of a couple of parts, 650V no reverse recovery does not hurt.

At a 40V rating, why did the original diode fail?