Hi,
Fiddeling around with one of my ZTE MF287+, I accidently disabled the modem by changing the file etc/init.d/usb on the modem. Under OpenWrt 23.5.4 there is no modem anymore, reflashing the backup of the Original software and resetting to factory (over web-interface as well via telnet via exploit) brought no change. The modem is gone from the routers OS. Various other diagnostics and approaches (adb/mncli/qmi-utils/..) led to the same result. Since no adb shell the zte_send_msg to factory reset is also unreachable.
So I am asking the community - any other idea?
If someone has a pinout of the modems (MDM9250 chip with a firmware labeld MDM9650 - not of the ipq4019) serial port I might be able to get there via serial console and overwrite the usb-file with the backup of the original. - If not then its a victim of science 
to find out how to activate mass_storage on the modems usb port for use with OpenWrt.
Apart from the modem all other functions are working.
There is a ZTE Framework Application that could maybe restore the modem and if you search hard enough, you can find a complete firmware dump including modem firmware dump files. I have, however, never tried to actually flash it.
Usually, these modems also have a recovery mode, but I have no idea how to enter it.
You might also see what happens if you plug the device into a USB adapter - maybe it's briefly there during boot.
And then you might want to check this out: https://eko.one.pl/forum/viewtopic.php?id=21790 (yes, different modem, but it might work nevertheless).
Thanks for the answer,
yes the polish site I read already 
- As I have a bunch of ZTEs MF287+ a modem dump is not the problem. The PCI to usb adapter for the modem is not solving the problem, as the modem is obviously in a wrong state.
So I need probably the serial console on the modem anyway, but have no clue where the port is/ pins are located (or any other means to reset the modem). Another possibility I found is to force implement (aka upload) the modem firmware update taken from an original ZTE/Hutchinson 3 bin image for the router, which I have not found so far.
The serial approach would also solve the problem in further researching the USB-port capabilities of the modem. I found reference designs of the ipq4019/MSM9250 combo including schematics and general feature descriptions, but no circuit diagrams from Qualcomm or third party vendors.
ZTE Framework is WIn only (not really a problem for a Mac/Linux user - already tested the "full" version - is similar to EDL-functionality) but does not like my PCI/USB Adapter.
So I might try to compile EDL (github.com/bkerler/edl - loader only for mdm9x5x) on a skimmed down OpenWrt directly on the router and get the modem into Qualcomm Emergency DownLoad mode.
Yes, the polish board contains the relevant test points to force recovery and edl mode - at least for the MF286 modem. Chances are they are in similar locations on your modem.