Inter-page shifts

Inter-page shifts

Inter-page shifts

The shifted pages during memory chip reading isn’t a regular situation, but sometimes in some cases with specific devices this problem may appear. In this article we will show you why exactly this problem occurs and how to easily fix it in VNR.

Good looking page ending.

Bad looking page ending.


There are several issues that lead to this problem:

1. Wrong voltage.

Fix:
First of all, you need to check the influence of voltage levels by increasing/decreasing VCC and VCCQ that the reader supplies to the device. This is the first step that will help to solve most of these problems.



Influence of the voltage can be easily checked in live-mode by opening the dump on the reader element. It allows to trace the real impact which particular voltage level has on the NAND chip.



2. Lack of power

Fix:
Find an additional power (VCCQ) on the device and connect it to the adapter.

To find the additional power, you should:


  • Connect the SD interface to the PCB and insert it into the card reader, thereby supplying power to the whole device. 

  • Then you need to find the wide tracks on the NAND interface and test continuity with the main power (VCC) of the SD interface. If the tracks are bridged, it means that these are the main power tracks, we are not interested in it. On other wide tracks that are not connected to the main SD power supply, you need to measure the voltage (black probe to the ground, red to the track). The VccQ auxiliary power should be between 1.8 and 3.3 volts. Tracks in which the power will be below 1.8 belong to controller's circuit and we are not interested in it.


3. Wire length
Fix:
The length of the wires from the device to the PCB should be as short as possible. Unnecessary wires should be removed from the NAND interface.
In general, the long wires are bad for signal quality (synchronization/delay). The longer the wire is, the more it interfere with other signals.
Additional unnecessary wires also badly affect the quality of the dump.


Below is an example of a photo with a proper soldering and length of wires.


4. Excessive wiring.

Fix:
Disconnect all wires from the SD/USB interface of the device.

There are situations when all the previous advice did not help. In the last step, you need to unsolder the SD interface from the device and look again at the end of the dump page.







Summary


Paying attention to the most common things may save you a lot of time. Many of us, engineers, too often ignore basics, just because "we know stuff", "we do it for years and never got a problems", "it always worked like that", "soldering looks fine", etc...


Always check the basics!



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