Ok, so having managed to get the real floppy drive & cable working as the internal drive on my H4 (so it boots from the floppy & can run sysinfo, Yartt & Gembench OK), I've now tried the same drive & cable (and floppy disc) in my H5 but still get the bombs on booting with a floppy in the drive.
I've then tried swapping the DMA, the 1772 & the YM2149F from the working H4 into the H5 but with no noticeable change in behaviour.
I'm using the same CPU & SIMM (both sourced from Exxos), keyboard, ROM & PSU as well as the other chips mentioned above in the working H4 & failing H5.
With no floppy in the drive at boot, it shows the desktop OK but them bombs when I first try to access a floppy.
It's a 720k floppy drive from another STFM, there's no PAL for the HD mod (yet - keeping things simple until it works & will then expand it in stages to ensure it still works as intended), jumpers set to boot from internal Floppy A, both drives 0 & 1 forced to 720k.
Using TOS 1.04 & that reports the single Floppy & 4M RAM (it's the modified image from
@rubber_jonnie IIRC, so it may also support booting from IDE though I've not yet tried that.)
There is no ACSI connector soldered in yet, so I've not had chance to test the HDD. Also I've not yet bothered with the blitter (jumper set for no Blitter)
I've not yet done the 3.3v regulator or audio mod on the H5 either (but doubt they are related to the non-booting issue).
Images below which hopefully show the jumper positions & also the ROM selector jumper, RTC link, Flashy clock link etc., so if anybody has any suggestions for the next step I'll be most interested to hear them!
IMG_20210815_162639413.jpg
IMG_20210815_162632302.jpg
IMG_20210815_162625301.jpg
IMG_20210815_162617431.jpg
I tried to follow the steps from other successful build logs...but ended up having to copy the jumper positions from my H4, so it's entirely possible one or more of those is wrong!
My plan is to bring a 'scope home from work on Tuesday & see if I can spot any differences in activity when the floppy is first accessed between the H4 & H5 boards...