Help Identifying Diode?

[Tenson]

Hi Guys,

I need to fix a mic channel on my M-Audio soundcard and I think following a bit of a PSU upset some diodes that protect the input of an op-amp might have blown. The application note for the op-amp (INA163) says to use 1N4148 but the circuit in the soundcard has sot-23 types.

They say WV4 and then at a right angle to that in smaller text '73'. I've read that WV4 means a schottky barrier diode but I've no idea what sort to get to replace it. Can anybody help?

 

[jaycee]

BAT54S

 

[Tenson]

Hi, thanks for the fast reply. Could you let me know why it is S and not A? How do you know?

 

[jaycee]

TBH, I googled it but have seen BAT54 used many times for this sort of input protection. I guess you need to figure out the pinout, but this should be fairly easy.

The diodes will be arranged so that they are connected to the power supply pins. One diode will be anode on the input pin, cathode to +V, the other diode will be anode to -V, cathode to input pin. Just test which pads on the pcb connect where when you unsolder the blown diode.

I would test the card by just removing the diodes and see if the input still works first. You may have further damage.

 

[jaycee]

basically any diode would work, the BAT54 was probably chosen because it is a common dual diode available in a convenient package. Being Schottky it also has lower capacitance, which is better for audio quality as it avoids capacitive loading and forming unwanted lowpass filtering.

 

[Tenson]

Thanks, I'll have a closer look at what pin connects to the rails.

 

[Tenson]

You are quite right, it is BAT54S, not A.

Any idea what the small 73 text on the parts means? Ahh I just found it is a manufacture date.

Thanks again! I hope I can get it working, those INA163 are not cheap! I can't complain that M-Audio use cheap bits.