FDD/service test cartridges?

Look for the service manuals, such as 8250, 8280 or so.
You will read how to use those carts and disks.
Inside MSX2 models, there is a switch or a jumper to disable internal BIOS and use one external slot as BIOS.
So, ROM code has to me burnt in first page (0x0000 and above).
No special loaders nor tricks.

I added +5V and ground to the ROM IC but still does not boot from it. There is no service switch on a VG-8010, the repair manual talks to put +5V onto pin20 on the internal ROM to disable it. That's working, when I put +5V onto pin20, I get a black screen. When putting the STC board, it does not change anything, I have the same black screen, so I assume it is not reacting correctly.
I will re- check my soldered connections on this STC board again, so I'm sure I have connected all correctly.
And look into the service manual for a 8250 or 8280 for more detail.

Yes, also good point, A14 should not be there. This is something to figure out. I will need to find some resistors and try again.

Finally I received some TMS27C128-15JL eproms and programmed one with the STCMSX1P.ROM image successfully.
So I plugged it in my proto board, disabled the internal rom, and tried to boot from the proto board.
Nothing seem to happen, the screen stays black.

Measuring address/data/control signals on this proto board is also not easy, especially when it's plugged in the cartridge slot.
So first, I'm trying to understand and figure out how the original schematics work.

Starting again on the Hans Otten mirror site:
https://hansotten.file-hunter.com/special-msx-hardware/phili...

Note this short explanation about the MSX1 test cartridge:
In the service cartridge for MSX1 there are, besides the ROM, two more IC’s, a 74LS32 (address) and a 74LS74 (flipflop) to select one of the two ROM banks.

So it says there are actually 2 ROM Banks to select ?? Why ? Is it meant for different MSX1 machines with a different start address ?
When dumping the ROM file, I can indeed discover 2 ROM banks, one from address 00000000h to address 00000ff0h and one from address 00002000h to address 00002ff0h.
Both seem to be identical (at first sight) and are about 4kB big in size.

A 74LS32 is an OR gate, meaning it's output will only go LOW when both inputs are LOW.
In this schematic /OE (output enable) will go LOW only when /RD and /MERQ are LOW.

A 74LS74 is a flip-flop and might be used as a sort of time delay?, so that address is ready before enabling the test ROM
Because PR is always HIGH, the output can be only go low when D0 has become LOW ??
This part I don't understand. It can only enable the ROM (/CE) when D0=LOW and A15=LOW ?
A15=LOW means all addresses below 32768
But why D0=LOW to enable the rom chip ??

So is this by mistake or can someone give more clarity on this ?
There are other errors on this schematic, like VCC for 74LS74 is pin14 and ground is pin7 and not pin16 and pin8.
Then there is A14 when the ROM is a 27C128?

Or, has someone the real STC cartridge open and could confirm the schematics ?

The RA1 15k resistors are pull-up (connected to +5V) right, to stabilize data on the databus ?

Pictures of the Philips Service Cartridge: