does anyone here have a dms 4 se pro on a version 7 ps2>?
Yes. I have a DMS4proSE (with ToxicOS) in my v7 SCPH-39004 PS2.
or maybe someone with the same problem?
psx backup worked once but has not worked since.
I tested it again right now with a PSX backup of FF7 (UK) disc 1, and it worked fine.
I launched this the same way I do all discs nowdays, by first booting into uLE (by Dev1), inserting the disc and waiting for the disc status to stabilize, before giving the uLE command "MISC/PS2Disc" to start the booting.
Note that for such an operation with modchip active a PS1 disc will falsely be displayed by uLE as a "PS2 CD" type instead of the correct "PS1 CD" type, due to modchip interference of the detection. But this does not affect the ability of uLE to boot a PS1 disc correctly.
After the above test I also tested the normal DMS4 method of booting a PS1 disc, by holding the 'Select' button pressed during power-on/reset, and this also works fine for me.
If both these methods fail for you, then something is seriously wrong with your chip's functionality, and if all wires are properly connected this could mean that you need to reflash the chip.
For some reason these chips seem to need occasional reflashing to work reliably, though I never got quite the problems you describe. But I have had other problems, such as unreliable Dev1 booting (freezing instead etc) which disappeared again after reflashing. And I really think it may be random which part of the flash memory deteriorates this way, so it may very well show the symptoms you have instead. So if I were in your position I'd definitely try a reflashing.
But don't do it without first checking that all your wire connections are correct.
Because if you flash the chip incorrectly you may fry it for good...!
I'm pretty sure it's the pin I've marked in red, but not 100% on it. It's been so long since I've screwed with this, and I can't seem to find the old diagrams.