MAX7221 with "stuck" digit?

[soonerdave]

I have a fairly simple project using an Arduino to feed a MAX7221 chip that drives eight 7-segment LED's, in a set of four double-digit displays.

I sent down a very simple sketch that does nothing more than run the digits 0-9 on each digit in sequence, and it all works just fine - with one curious exception. Digit 5 seems always active, all segments lit - brighter than the other 7 displays and seemingly always showing a shadow or "glimmer" of the adjacent digit (which displays correctly).

I traded the digit select wires from the pair exhibiting the behavior with an entirely different working pair, and the problem goes with it. The original set of digits then worked normally. That leads me back to the pin driving the digit. I replaced the wire from the pin to the digit select, with no difference. That's leading me to the 7221 itself and the pin driving the suspect digit.

I would describe the behavior as the digit always being pulled down by the 7221 (connected to the cathode), as if internally the chip has developed a flaw that leaves that digit stuck "on." Bizarre as it seems, I was just wondering if anyone else had experienced a similar problem with this particular chip. Mostly a curiosity, because I've inadverntly fried a couple of these chips before with careless application of wrong voltage, but that normally results in the whole thing being toasted, not one of the eight displays getting "stuck." Just seemed a little odd.

Thanks,
sd

[CrossRoads]

Does seem a little odd.
Most folks use MAX7219 as they are less expensive, but they work essentially the same.
Check your wiring, maybe you have a digit line accidentally grounded, or shorted to another pin.

[gilshultz]

It could be ESD damage. You can damage parts with ESD but it takes time for it to manifest itself, from nanoseconds to years. Why not try a different chip after you have determined there is no short or opens. A great tool would be a logic analyzer, you can get a cheap 8 channel china one for less then $10.00 delivered from one of the china vendors.