SMT diode ID help

Hi. I need help identifying a diode. For context, this is on a small digital drum machine without a schematic available. It was damaged after the incorrect power supply was connected. It takes a 12VDC power supply of at least 300mA.

The diode is blown apart and the unmarked anode end connects directly to the positive power input. The cathode goes to ground. It’s about 1.7mm long and 1.4mm wide. It has a marking that says B1.

Hopefully this is enough info to find it? If we need more clues and “B1” isn’t enough, there’s a power stage that has a 78L05 and a 78L06. I can hunt more in that area if that helps determine what specs the diode should have.

Thanks for any help.

I’d suggest it’s likely the other way 'round. Such an arrangement is one technique for providing protection against a reversed supply connection. If that’s the case, most any diode that fits would probably work. Sounds like an SOD323 or variant based on the dimensions given.

Note however, that if the diode failed to an open state in the act of protecting against a reversed supply, it would cease to provide that protection. As such, there’s a fair chance that the damage extends beyond this particular diode.

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I get these mixed up and triple-checked, but to check again: The unmarked (anode?) connects directly to the +DC input. The marked side (cathode?) goes to ground.

Yes, there is clear damage elsewhere, but this seemed like a starting point. There’s a logic chip that is visibly blown but I can still read a part number. Thought I’d try to clean up this diode (and that logic chip) before testing other parts in the power stage.

All (re)said, you think an SOD232 seems likely?


SOD323 was a size that I settled upon when searching, too: [ SOD323 Package Information ]. I wasn’t confident in any specific part number even with the B1 marking, though.

I understand what you describe as being represented by the below. I suspect that you’re savvy enough to understand why this probably isn’t quite right…

If the cathode mark is indeed connected to ground/supply negative, the deceased item would likely be a bidirectional TVS diode, rather than a normal rectifier type. That would make some sense from an ESD protection standpoint, and also explain release of magic smoke if a supply of higher voltage than specified was connected.

That scenario would not bode well for repair prospects either, as in that case each weak link in the chain would blow successively until one failed to a sufficiently hard short to drag the offending supply into submission. One of these might be a possible fit; I’d look at what the limitations of the downstream components are and suggest a 15v standoff type if it were tolerated.

If you have some idea of the specs of the incorrect power supply that was connected, that might give you some more info as to how far the damage might extend…

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