PCF2127 RTC RAM does not work

[dave_harmonjr]

I recently ordered 20 custom boards from a board house and 6/20 the RTC's (PCF2127) ram does not work. If I write to it, and then read back from it I get all 0's. On the other 14 boards I read back exactly what I wrote. The chips would have be initially ordered somewhere around mid to late 2019? I think. I noticed another post where someone had the same exact issue as me and there were some replies asking him to fill out a document to send in the chip for analysis.

I was wondering if there is any errata list for this chip? I could not locate it. They all are exactly the same firmware, circuits, components, produced side by side. Every other function of the chip seems to work fine. Seems really bizarre to have that many not work, but also have that many work as well with very simple circuitry and assembly.

One of the chips have this written on it:

"PCF2127T

AFF173

1                Q5

knD19202"

I attached a picture of the circuit schematic.

[tkhansen]

We experience something similar, so I'm interested in knowing if you reached a solution or conclusion?

[guoweisun]

Two questions for you:

1: Do you test the fail and good boards by switching RTC parts?

2: Did you damage the chips in the process of making the boards?

[dave_harmonjr]

I swapped the RTC on a good board to a bad board and the RTC RAM worked on the "bad" board. So it appears it is a chip related issue. I got the reflow temp profile. It is attached.

[guoweisun]

Do you mind to share with us your schematic?

[dave_harmonjr · Accepted solution]

I bought new chips and replaced all the ones on the bad boards and they all work now. Seems to just be a bad batch of chips from NXP to mouser from late 2019.

[dave_harmonjr]

1. No. I will do that right now. Good Idea.

2. I asked the production board house for a report on their process for assembling these boards.