Getting inconsistent reads with a Raspberry Pi

[David Hobach]

Dear all,

I'm trying to read a MX25L3206E and a MX25L6406E in-circuit (laptop) 
with a Raspberry Pi Rev.1 using a POMONA 5220 SOIC clip.
flashrom v0.9.9-r1955 on Linux 4.9.35+ (armv6l)

Unfortunately I keep getting images with varying md5sums.

Moreover, when switching between the chips, flashrom always detects the 
chip it was last connected to (i.e. not the real one) and the MX25L6406E 
is not correctly detected at all in general (incorrectly detected as 
some other chip).

If anyone knows those symptoms, I'd love to hear a comment!

All external power sources are disconnected (incl. CMOS battery). The 
3v3 of the Pi is used for powering. All 8 Pins were connected (incl. 
Hold and WP to 3v3).

What I checked so far:
- The factory images on the chips work.
- SPI loopback on the Pi works (MISO <--> MOSI).
- Cables are relatively short (tried 28cm and 2* that with a 10k Pullup 
on MISO - the latter didn't seem to change much, but I'm not 100% sure yet).
- Reducing the clock speed didn't seem to make a difference (e.g. 
flashrom -p linux_spi:dev=/dev/spidev0.0,spispeed=1000 -r flash03.bin -c 
"MX25L3206E/MX25L3208E").

I didn't try yet:
- external 3v3 PSU
- laptop power (I actually connected the AC adapter once without 
booting, but it didn't seem to power the chip - I didn't measure 3v3)
- putting a 22pF capacitor somewhere (I'm not sure where exactly?)
- unsolder the chip - I'm trying to avoid that as I'm not good at that...

Do you have any other ideas? Maybe I'm missing something obvious?

I haven't done this for a few years, so any help would be greatly 
appreciated.

Thanks & Kind Regards
David