Author Topic: NHD-2.7-12864UMY3 - VDD short to VSS  (Read 4498 times)

EK701

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NHD-2.7-12864UMY3 - VDD short to VSS
« on: July 26, 2014, 06:44:27 PM »
I've been using an NHD-2.7-12864UMY3 to do a bunch of prototyping and I think I've managed to cause an electrical issue with it.  With the display not connected to anything, there is a short between VDD (pin 2) and VSS (at any VSS point on the display PCB).  Resistance is about 45 ohms.  I've visually inspected everything, but I don't see anything obviously wrong.

Is there any way for me to trouble shoot this (schematic available?)

EK701

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Re: NHD-2.7-12864UMY3 - VDD short to VSS
« Reply #1 on: July 29, 2014, 02:18:01 PM »
Anyone have any ideas?  Does New Haven participate in the forum?

Michael_L

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Re: NHD-2.7-12864UMY3 - VDD short to VSS
« Reply #2 on: July 29, 2014, 04:14:03 PM »
VDD and VSS, of course, should not be shorted.  I am not sure what testing you have performed that has caused this, but I'm sorry a schematic is unavailable.
My guess would be possibly try replacing one of the decoupling capacitors C1/C2, or at at least checking there is no solder-short present there, or anywhere else for that matter.
Otherwise, you can order another display to replace the one you have damaged.

EK701

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Re: NHD-2.7-12864UMY3 - VDD short to VSS
« Reply #3 on: July 29, 2014, 09:30:31 PM »
Just a follow up.  I removed C1 and C2 and the short still persists.  I did find a few interesting things with further testing.  With 3.3VDC applied to pin 2 and pin 1 connected to ground on the power supply, I was able to consistently measure 45mV on all ground points.  Additionally, as soon as I connect the display to 3.3VDC, the voltage displayed on my multimeter drops to .74VDC.  As I probed around the display PCB, occasionally I would see 2+VDC where I should see 3.3VDC, but it would just be a fleeting reading, then drop to .74VDC.  Putting the scope on various points did not show anything of interest - no ripple, no AC, etc. 

One other interesting point is using my multimeter to check continuity, on the tone setting, produced a clear steady tone anywhere on the ground circuits (with the negative lead connected to pin 2).  However, when I put the positive probe onto any part of the 3.3v circuit, it produced a buzzing tone.  Not sure what that means or if it's even of interest. 

I also checked all the components closely under magnification and did not see any that appeared to be burned.  I guess at this point, I'm going to write off this display and purchase another.  Unless someone has any other ideas.

EK701

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Re: NHD-2.7-12864UMY3 - VDD short to VSS
« Reply #4 on: August 24, 2014, 09:35:12 PM »
It looks like U1 is the problem.  I couldn't read the marking on it.  Can anyone tell me what this device is so I can replace it?  On a NHD-2.7-12864UCY, the same device (U4) is only marked BLCVA and I can't find any info on that.

Michael_L

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Re: NHD-2.7-12864UMY3 - VDD short to VSS
« Reply #5 on: August 26, 2014, 04:16:17 PM »
Linear Technology - LT1615

dotmatrix

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Re: NHD-2.7-12864UMY3 - VDD short to VSS
« Reply #6 on: August 26, 2014, 05:57:26 PM »
sounds like you fried something, unless you got a smt soldering iron, your better off buying a new module. if you do have a smt tip, you can try and desolder the lt1615 and replace it. fyi, i always use a diode in series with the positive side of my power supply to avoid reverse polarity or shorting out the regulator, etc

EK701

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Re: NHD-2.7-12864UMY3 - VDD short to VSS
« Reply #7 on: August 26, 2014, 09:36:52 PM »
Thanks!

 

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