Unknown component inside the SCC-A10 attenuator

[flongb]

Hello,

I've been given a SCC-A10 attenuator for a class project but it appears it is not working propertly. I identified the component that died but I cannot for the life of me find its reference or nature even.

It is a 3 pins SOT component with "NDEN" written on top. The bottom left pin is unused while the top pin and the bottom right pin are linked by a mistery component.

It seems to be some kind of diode(s) with a threshold voltage of 0.6V from bottom to top and 0.55V the other way around.

Could it be parallel diodes? Or maybe some kind of weird zener? I don't think it's a transistor but I might be wrong.

Thank you for your help

[AnalogKid2DigitalMan]

CR typically means 'current rectifier' thus some type of diode.

Looking at the schema of the module, I would guess it is part of the over-voltage protection, perhaps a Zener.combination. 'NDEN' is not enough information to get any further details. I suspect that CR1-4 are identical units.

[flongb]

The whole block is indeed an overvoltage protection as explained in the datasheet but if it were a single zener diode, because CR 1-8 are all the same, the circuit would only be two back to back zener (for each "row")

And I don't think that constitutes an overvoltage protection (it would if they were connected to the ground though). 

So a combination it is, I thought it might be parallel diodds

But thanks a lot for your answer, I'll use that CR hint to see if I can find the component online. I've been at it for hours already so Im not very hopeful but we'll see

[Henrik_Volkers]

If you want to fix it... (since it's not your you should ask the owner 😉 )

I would unsolder a working one and use a <20$ component-tester like this one,

or dig deeper into the schematic to to see if it's a double diode  or a FET connected as a low bias current diode. By the number of them (2 for each input) I vote for a FET....

these testers are a cool toy ..

[flongb]

Alright so I aquired a tester and the component (which I had unsoldered a while ago) and it is still unknown.

I'm at loss here, I've spent so much time trying to figure what it is but I've made little to no progress. The schematics doesn't help either, the only relevbant information in the datasheet is that the whole block in an overvoltage protection.

 

Do you thinkI could contact the NI support? Or any other ideas?

[Henrik_Volkers · Accepted solution]

Tested a "working" component?  Also between only two pins? (However double diodes are detected too IIRR...)

You can always contact NI and ask them for more information on that part. I wouldn't expect answers for all devices and in the forum, but maybe in a more private mail ??

My next adress would be the eevblog and add the pcb picture and one from the backside of the PCB

[flongb]

Yup, I tested a working component (CR 2) in every way imaginable, still unknown. I asked people around me as well and they have no clue, this is getting infuriating.

I'll email NI and will also post on that forum you linked me.

Thank you for your time, you've been really helpful eventhough I haven't quite resolved my issue yet

Crosspost on eevblog 

[flongb]

the people at eevblog were able to tell me it was a MOSFET

[Henrik_Volkers]

I would order 10 and replace at least all four of the first channel.  If one is fried all others are questionable and it's quickly done.

You said you checked agains CR2 ... same channel 😄