strange issue with SD slot and Speedtest

[Dream88]

Hi, this is my first post on this forum.
i have installed an internal SD slot on two of my dreamcast with that schematics.

that two sd slots works (apparently) good with iso loader run iso from sd, but when i select Speedtest the result of SD test is in red color: "can't write to file".

after tried the test i put the sd card in PC and i see a file called "speedtest.testfile",sometimes that file are 0kB or 15,9MB.

i've been tested some cards:
1GB Transcend 16K cluster
2BG Transcend 32K cluster
SDHC 4GB SanDisk (i don't remember the cluster).

my console are:
NTSC-J VA1 board with stock bios
NTSC-U VA1 board with stock bios

what's wrong?

maybe an incorrect installation of SD slot?
a bug on Speedtest program?

i have another question respect of SD slot installation,
I read on the net that it is sometimes necessary to remove five SMD capacitors on the bottom of the motherboard near the serial port of the dc to be able to function properly sd slot, that's true???