Thread: Repairing Lilliput touch controller / Fried Zener

Originally Posted by rando

... Maybe that 5V isn't the label for the pin in which case this zener may actually NOT be foward biased (a good thing). I guess I better double check this when I get home. It was like 1AM when I looked at it. argh.....

OK, that was it. Who would have guess that the red wire was ground and the black wire was 5v. Apparently the 5v did refer to the zener and thus it was reverse biased ... the planets are aligned again.

Armens replacement zener came in today, it's installed, and my touch controller is safely working again. BTW, the markings CJ5.1 appeared on the part and I conrfirmed it to regulate around 5V.

Thanks to each of you that helped and a special thank you to Armen for providing the replacement part.

Originally Posted by rando

I fried my Lilliput touch controller. Looking at it, there is a diode across the +5v rail and ground that got fried. When i removed the diode, the controller worked again. Accoring to the board silk screen, it's a foward biased zener. I'm not sure I understand what that zener would be doing there. If forward biased, would that essentially short the USB +5v rail?

In any case, does anyone know what it is? I assume it was 5.1v zener (reverse biased despite the what the silk screen says) there to protect against an overvoltage. This is supported by the theory that my t/s controller started working again once I removed the fried part.

Rando,

My controller died too. Looked at it and there was some indication of the over voltage (compared to the other pictures in this post). I removed the zener and mine still doesn't work. I saw the one side was 5v rail and other was ground. did you just leave the zener off and it worked again, or did you put something in its place until the replacement from Armen got there?

Batman

Originally Posted by Batmanatthenewb

Rando,

My controller died too. Looked at it and there was some indication of the over voltage (compared to the other pictures in this post). I removed the zener and mine still doesn't work. I saw the one side was 5v rail and other was ground. did you just leave the zener off and it worked again, or did you put something in its place until the replacement from Armen got there?

Batman

Once I removed it, the touch kit worked again (albeit unprotected from any kind of power issue). I assume this means the zener fried into a short, or at least a near short. It crumbled into pieces as I unsoldered it. The replacement part was important to restore the limited over / reverse voltage protection.

If your controller isn't working without the zener then I assume you have other issues. It's fairly lucky (in my case) that the zener burned to a short. Once it burns to an open, you'll no longer have any protection and your ICs are next in line to get fried. Check the data sheets on some of those components. They are fairly clear that they cannot survive even momentary spikes beyond 5.5V.

In other words, the zener provides only limited protection and eventually the controller will be killed by errant input voltages.

Originally Posted by Curiosity

Well, this is what it looks like when it's shorted from over voltage.

Yep, though mine was much blacker than that. It scorched the circuit board and even melted the solder joints.

Originally Posted by superdude

Who or what is armen?

It might help if you actually read the thread before you post.

Originally Posted by digitalww

I can probably take this component from one of the bad controllers I have and send it to you, for a $1

What do you think?

Armen

As you can see, Armen is DigitalWW. DigitalWW is Armen. I think that about clears it up.