Neo Geo MVS not booting, any ideas?

I hope the NEO-IO that you mentioned is the NEO-"EO"... this is a bit confusing - neogeodev has no info on an "IO" chip, but in the schematics of the mvs there it is...

I tested pretty much every connection twice:

CPU(A1-A15) -> RAM1(A0-A14) -> RAM2(A0-A14) -> SP1(A0-A15)
RAM1(A0-A14) -> RAM2(A0-A14)
CPU(A17-A21) ->NEO-C1(A17-A21)
CPU(D0-D15) -> SP1(D0-D15)
CPU(D0-D7) -> RAM2(D0-D7)
CPU(D8-D15) -> RAM1(D0-D7)
CPU(D8-D15) -> NEO-C1(D8-D15)
RAM1(OE,WE) -> NEO-C1(RAOU,RAWU)
RAM2(OE,WE) -> NEO-C1(RAOL,RAWL)
CPU(VPA,DTACK,RW,UDS,LDS,AS,CLK) -> NEO-C1(VPA,DTCK,RW,UDS,LDS,AS,6CLK)
SP1(A0-A15) -> NEO-E0(A1-A16)
SP1(OE) -> NEO-EO(ANO0)
SP1(A0-A3) -> U14/LS245(A1-A3)
SP1(A0-A3) -> U7/LS245(A1-A4)
NEO-EO(ANO0) -> U7/LS245(Q1)

plus all VCC-connections of course.

Scoped the CPU:
VPA - bouncing
DTACK - high
RW - bouncing
UDS - bouncing
LDS - bouncing
AS - bouncing
CLK - 12MHz waveform

WRAM (OE,WE):
RAOU - high
RAWU - high
RAOL - high
RAWL - high

The replacement of the WRAM did not change anything, the system is still in "click-of-death"-mode.

 

https://wiki.neogeodev.org/index.php?title=NEO-I0 (it's mislabeled)
https://wiki.neogeodev.org/index.php?title=NEO-E0

Did you check that E0 ANI0 and ANI1 have continuity to the C1?

Because most of the address decoder outputs seem OK, time to check the C1's inputs too.
https://wiki.neogeodev.org/index.php?title=NEO-C1

I'd try DTACK and 68KCLK's continuity first.

BTW, have you tried reflowing the ASIC solder joints? That's a quick fix often times.

 

I fucked it up :-/
I found a matching 68k on an old mega cd mainboard and transplanted it since the "click of death" could be caused by a bad cpu, so I did it just in case.
When I reflowed pretty much every ic with my hot air rework station I lost the sync and the screen now is just unstable. Because I still hear the clicking on the speakers I know that the fault still remains.
I traced the sync from LSPC2/Pin 150 to the LS32/Pin1+Pin2 and I'll work from here...
Not the greatest update but at least an update :-/
Thanks so far!