Zero ohm resistor

[pcpete]

have you guys seen a 0 ohm resistor with a "Z" or "N" on it as opposed to a "0",? I come across one which all logic says it has to be a zero ohm , but I can't seem to verify it.

 

[britechguy]

Photo, please?

http://www.learningaboutelectronics.com/Articles/Zero-ohm-resistors

Those I have seen that are barrel style always have the single black line at the center of the body.

The minute I hear Z I go for a Zener diode, but without any photographic evidence that's the worst kind of SWAG.

 

[Moltuae]

Is this on the component itself, or on the board next to it?

If it's a component reference on the board, Z can refer to inductance but I'd expect to see a number too. If it's printed directly on the component, without any other numbers/letters, it's possibly a tolerance rating, in which case the component is likely to be a ceramic capacitor.

 

[HCHTech]

I had to look that up because my first thought was "Umm, zero ohm resistor....isn't that otherwise known as a 'wire'?"

Turns out that is how it functions - used to connect traces on a board. So many questions - why would a board be designed to require one of these? Why wouldn't the traces be connected directly on the board? I imagine that the reason would be for different configurations available with the same board...I guess. Odd.

 

[Larry Sabo]

Sometimes they serve as fuses, e.g., on HDD PCBs.

 

[britechguy]

@HCHTech,

I had precisely the same reaction, but several discussions of same pointed out this was primarily because of robotic manufacturing techniques. Wire almost always needs "the human touch" when we're talking about the space constraints on PCBs. And even if you use "the thick wire" like is on the end of these resistors, bent appropriately, it's very difficult for mechanized assembly machines to pick up and handle.

These non-resisting resistors are of the same general size as other components used on PCBs that the manufacturing equipment is designed for so when they need a wire . . .

 

[Moltuae]

why would a board be designed to require one of these?

Zero ohm resistors can be useful for resolving routing issues because you can run tracks under them. An experienced board designer should be able to avoid them however, especially on multi-layer board designs. I've used them on many of my own board designs but for different reasons: If you have a board design that has a number of different build options/configurations, zero ohm resistors can provide a way to manufacture different versions of the same board just by changing the Bill of Materials.

 

[pcpete]

I will post a picture tomorrow. With thinking about it, it must be a fuse not a zero ohm resistor

 

[pcpete]

this is the component. It has to be a fuse. This is from a 2.5" hd board

Dropbox

www.dropbox.com

 

[Moltuae]

That does look like it might be a fuse, given that it appears to be connecting a power-plane to a couple of external connector pins. The Z/N is likely to be some rating code in that case.

 

[pcpete]

strange thing is the fuse was blown, but the tvs diode was not tripped. In my experience, first the diode trips, which shorts the power rail to ground, then the fuse goes after. Jumped the fuse, checked for shorts, then spun it up. The drive is spinning yet unresponsive as the client opened it at one point. If he would have brought it to us first before opening it, I am sure we would have got his data.

 

[Larry Sabo]

It'll reset itself once power has been removed

I don't believe that's correct. There's a reason they're called sacrificial diode. All the ones I've seen have been dead as can be, fully shorted.

 

[Moltuae]

strange thing is the fuse was blown, but the tvs diode was not tripped. In my experience, first the diode trips, which shorts the power rail to ground, then the fuse goes after.

Only if the cause was a voltage discrepancy (excessive or polarity reversal) because the diodes are usually parallel to the circuit they're protecting. However, excessive current flow, one that is not caused by excessive voltage (eg a short), can pop a fuse without affecting protection diodes.

 

[pcpete]

How could you tell? It'll reset itself once power has been removed, just like any thyristor/triac-based crowbar circuit.

I thought it will go to 0ohm after it is tripped.

In any case, there's little point in replacing the fuse without diagnosing and solving the problem that caused it to blow in the first place; for most computers (and most users) that makes it cheaper to pronounce the machine irreversibly dead and move on.

the client was trying to recover data and was using an external connector. It was plausible that it somehow shorted the fuse

 

[Larry Sabo]

the client was trying to recover data and was using an external connector. It was plausible that it somehow shorted the fuse

A common error is to use a 19v connector instead of the 12v it should be. That blows the diode and/or fuse.