I have a cheap and nasty commercial SPI-based audio player which I'm playing with, for practice. It's based around a blob microcontroller and an 8-pin 25F SPI flash chip. I've removed the chip from the board so I can dump it, and have soldered extension wires onto the board so that I can get it working again without having to solder the chip back on. Now, of course, it doesn't work.
The SPI clock runs at 8MHz and my wires are about 4-5cm long. Looking at the result with a scope shows that the waveforms look noticeably grottier than they did before I removed it. Screenshot below; lines are, from top down, CS, MISO, MOSI, SCLK.
So, what could be wrong? I've checked the obvious things like making sure of the pinout, continuity, correct power, that the flash chip does actually work, etc.
capacitance: is that really an issue for a 5cm wire? Can I just rule this out because the wires are too short --- at what point does it become an issue? 8MHz is faster than I expected, TBH.
crosstalk/noise: likewise, 5cm? The traces on the board itself are maybe 2cm long and are much closer together than my extension wires. The wire resistance itself should be negligible too, right?
There seems to be a lot of noise coming from somewhere...
Edit: Apparently I'm not going to be able to get away without posting a picture of my monstrosity, so here it is. Enjoy. The flash chip is in the ZIF socket on the left. The wires are solid core.