Product ID: 3295 (PCF8253) PCB Error

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drhatch
 
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Product ID: 3295 (PCF8253) PCB Error

Post by drhatch »

The PC board on my recently-purchased PCF8523 breakout board has an error.

SHOULD BE: Under the battery holder, the PCB should have a center, round gold pad that is surrounded by an annular ring made from bare FR4 material. In other words, there should be a wide donut-shaped ring of BARE board material around the center gold pad. (The pictures on the product page show this very well.)

ACTUALLY IS: The board I received has a conductive gold annular ring around the center pad, instead of the bare PC board ring.

PROBLEM: The CR1220 battery has a negative terminal that is VERY SLIGHTLY raised from the edge of the coin cell, and is an insufficient feature to mitigate the PCB problem. The edge of the coin cell is the positive terminal. The conductive annular ring causes the cell positive edge to become SHORTED to the negative terminal when inserted into the coin holder.(!)

I don't know if the dead short could cause a fire hazard, but it is a very bad thing to do to a coin cell.
In any event, the product will not work as intended/advertised (because there is no cell voltage present because of the short circuit).

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tepalia02
 
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Re: Product ID: 3295 (PCF8253) PCB Error

Post by tepalia02 »

Hi, is it still under warranty? If so, I think you should contact them for a replacement.

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adafruit_support_carter
 
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Re: Product ID: 3295 (PCF8253) PCB Error

Post by adafruit_support_carter »

That change seems odd. Can you please post a photo of the PCB?

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drhatch
 
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Re: Product ID: 3295 (PCF8253) PCB Error

Post by drhatch »

adafruit_support_carter wrote:That change seems odd. Can you please post a photo of the PCB?
Pictures attached. You can clearly see the incorrect gold annular ring surrounding the center gold pad.
Please compare these to the product pictures on the website.

The conductive annular rings creates a conductive link between the CR1220 battery's positive and negative terminals, because the positive terminal wraps around the side and bottom of the cell.
pic_2.jpg
pic_2.jpg (51.82 KiB) Viewed 3318 times
pic_1.jpg
pic_1.jpg (106.74 KiB) Viewed 3318 times

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adafruit2
 
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Re: Product ID: 3295 (PCF8253) PCB Error

Post by adafruit2 »

hiya have you actually verified there is a short circuit on your battery? the bottom pad is ground, but should not end up touching the postitive terminal which is up top.

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drhatch
 
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Re: Product ID: 3295 (PCF8253) PCB Error

Post by drhatch »

adafruit2 wrote:hiya have you actually verified there is a short circuit on your battery? the bottom pad is ground, but should not end up touching the postitive terminal which is up top.
Yes, I have verified this with two different CR1220 cells.

You need to look at the cell -- the positive terminal wraps around the sides, and is present at the bottom of the cell. The negative terminal is proud of the positive terminal by only 0.52mm. Any slight misalignment of the cell will create a short *IF THE PCB layout has a conductive annular ring.* This is why the original layout has a bare PCB insulating ring.

The PCB as shown in the pictures on the website is proper, and safe. The current PCB is incorrect, and frequently creates a short.

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adafruit2
 
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Re: Product ID: 3295 (PCF8253) PCB Error

Post by adafruit2 »

it does wrap around, but it should not be flat against the bottom, there should be a slight lift. it could be your battery make is different enough from the ones we stock.
you have the older version of the PCB, where did you order it from?

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drhatch
 
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Re: Product ID: 3295 (PCF8253) PCB Error

Post by drhatch »

adafruit2 wrote:it does wrap around, but it should not be flat against the bottom, there should be a slight lift. it could be your battery make is different enough from the ones we stock.
you have the older version of the PCB, where did you order it from?
Ack! I thought I had ordered it from you (what I really want is your "Adafruit PiRTC - PCF8523 Real Time Clock for Raspberry Pi Product ID: 3386" but that is "Out of stock").
So I had ordered from someone else!

I am glad your PCB is correct!

Thank You!

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