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E4433B-11 Service Note - UND Waveform sequence SRAM failure

Question asked by smunaut on Nov 21, 2015

I have a UND board that was misbehaving. I found this service note and I ended up replacing the SRAM chips myself with 4 CY7C109B chips and this actually fixed it.

Now what concerns me is that the chips that were present were already CY7C109 ... and so I'm not sure what made them fail in the first place, but it might just make the new one fail as well.
At first I thought the service note was maybe referring to a bad bad of chips, but there are other CY7C109B on the board, used for the DSP RAM and they're the exact same, same date code and all and those work fine.

So does anyone if the SRAM failure is a design issue ? Like maybe it's driven in some improper way ? And is there anything to do to prevent it from happening again ?

Also, does the E4400-60753 contain CY7C109B chips ? or some other model ?